Download sreekala minor project 2016

SYNTHESIS, CHARACTERISATION AND SELECTIVITY
STUDIES OF CROSSLINKED POLYSTYRENE SUPPORTED
SCHIFF BASES
REPORT SUBMITTED ON COMPLETION OF UGC ASSISTED
MINOR RESEARCH PROJECT
MRP(S) ‐0285/12‐13/KLKE057/UGC‐SWRO
BY
Dr.N.B.SREEKALA
DEPARTMENT OF CHEMISTRY
SREE NARAYANA COLLEGE, CHATHANNUR
KOLLAM, KERALA‐691579
Submitted to
UNIVERSITY GRANTS
COMMISSION NEW DELHI
From
Dr. N. B. Sreekala
Principal Investigator,
UGC Minor Research Project,
Department of Chemistry
Sree Narayana College, Chathannur
To
The Accounts Officer
University Grants Commission,
South Western Regional Office
P.K. Block, Palace Road, Gandhinagar
Bengaluru- 560009
(Through Proper Channel)
Sub: Submission of the Final Report of the Minor Research Project.
Ref: MRP(S) - 0285/12-13/KLKE057/UGC-SWRO
Sir,
I am sending the final report of the work done on the Minor Research Project
entitled “SYNTHESIS, CHARACTERISATION AND SELECTIVITY STUDIES OF
CROSSLINKED POLYSTYRENE SUPPORTED SCHIFFBASES” along with all the
documents.
I request you to be kind enough to accept the report.
Thanking You,
Yours faithfully
Dr.N.B.SREEKALA
PRINCIPAL
S.N.College, Chathannur
UNIVERSITY GRANTS COMMISSION
BAHADUR SHAH ZAFAR MARG
NEW DELHI – 110 002
ANNEXURE III
Annual/Final Report of the work done on the Minor Research Project. (Report
to be submitted within 6 weeks after completion of each year).
1. Project report No. 1st/2nd /3rd. /Final: FINAL
2. UGC Reference No: MRP(S) - 0285 /12- 13/KLKE057/UGC- SWRO, dated
29-03-2013
3. Period of report: From 29/03/2013 to 29/12/2015
4. Title of research project: “SYNTHESIS, CHARACTERISATION AND
SELECTIVITY STUDIES OF CROSSLINKED POLYSTYRENE
SUPPORTED SCHIFFBASES”
5. A. Name of the Principal Investigator: DR.N.B.SREEKALA
B. Dept. and University/College where work has progressed: DEPT. OF
CHEMISTRY, SREE
NARAYANA COLLEGE, KARAMCODE P.O,
CHATHANNUR, KOLLAM.
6. Effective date of starting of the project: 23/09/2013
7. Grant approved and expenditure incurred during the period of the report:
a. Total amount approved: Rs.1,30,000/b. Total expenditure: Rs. 1,30,000/c. Report of the work done: (Please attach a separate sheet): A separate report is
attached
i. Brief objective of the project: Enclosure I Attached separately
ii. Work done so far and results achieved and publications, if any, resulting from the
work ( Give details of the papers and names of the journals in which it has been
published or accepted for publication) Enclosure II Attached separately
iii. Has the progress been according to original plan of work and towards
achieving the objective if not, state reasons: Yes
iv. Please indicate the difficulties, if any, experienced in implementing the project:
The characterisation of polymeric chelating resins and their metal complexes
were done by spectroscopic methods like IR UV &ESR. There was a delay in
getting the results on time.
v. If project has not been completed, please indicate the approximate time by which
it is likely to be completed. A summary of the work done for the period (Annual
basis) may please be sent to the Commission on a separate sheet : Final Report
is attached
vi. If the project has been completed, please enclose a summary of the findings
of the study. Two bound copies of the final report of work done may also be
sent to the Commission: Enclosure III
vii. Any other information which would help in evaluation of work done on the
project. At the completion of the project, the first report should indicate the
output, such as (a) Manpower trained (b) Ph. D. awarded (c) Publication of
results (d) other impact, if any: NIL
SIGNATURE OF THE PRINCIPAL
INVESTIGATOR
REGISTAR/PRINCIPAL
ANNEXURE IV
UNIVERSITY GRANTS COMMISSION
BAHADUR SHAH ZAFAR MARG
NEW DELHI – 110 002
UTILISATION CERTIFICATE
Certified that the grant of Rs.1,30,000/- (Rupees One Lakh thirty Thousand only)
received from the University Grants Commission under the scheme of support for
Minor Research Project entitled- “SYNTHESIS, CHARACTERISATION AND
SELECTIVITY
STUDIES
OF
CROSSLINKED
POLYSTYRENE
SUPPORTED SCHIFFBASES” vide UGC letter No. MRP(S) - 285/1213/KLKE057/UGC- SWRO, dated 29-03-2013 and 19-01-2015 has been fully
utilized for the purpose for which it was sanctioned and in accordance with the terms
and conditions laid down by the University Grants Commission.
SIGNATURE OF THE
REGISTRAR/ PRINCIPAL
PRINCIPAL INVESTIGATOR
STAUTORY AUDITOR
Receipts and Payments Account For Undertaking Minor Research Project under
Scheme
Receipts
Grant from UGC
Amount
1,30,000/-
Payments
Amount
1. Books
& 10,000/Journals
2. Contingency
10,000/3. Chemicals & 1,00,000/Glassware
4. Field Work & 10,000/Travel
Total
1,30,000/-
Verified with the books of accounts produced before us and found in agreement with
them.
UNIVERSITY GRANTS COMMISSION
BAHADUR SHAH ZAFAR MARG
NEW DELHI – 110 002
ANNEXURE V
STATEMENT OF EXPENDITURE IN RESPECT OF MINOR
RESEARCH PROJECT
1. Name of Principal Investigator: DR.N.B.SREEKALA
2. Dept. of University/College: DEPT. OF CHEMISTRY, SREE
NARAYANA COLLEGE, KARAMCODE P.O, CHATHANNUR.
3. UGC approval No. and Date: MRP(S) - 285/12- 13/KLKE057/UGCSWRO, Dated 29-03-2013
4. Title of the Research Project: “SYNTHESIS, CHARACTERISATION
AND SELECTIVITY STUDIES OF CROSSLINKED POLYSTYRENE
SUPPORTED SCHIFFBASES.”
5. Effective date of starting the project: 29-03-2013
a. Period of Expenditure: From 29-03-2013 to 29/12/2015
b. Details of Expenditure
S.No.
Item
Amount
Expenditure Incurred
Approved
Rs.
10,000/10,000/i.
Books & Journals
Rs.
ii.
Equipment
iii.
iv.
v.
vi.
Contingency
Field Work/Travel
(Give details in the proforma at
Annexure- VII).
Hiring Services
Chemicals & Glassware
vii.
viii.
Overhead
Any other items (Please specify)
TOTAL
10,000/10,000/-
10,000/10,000/-
1,00,000/-
1,00,000/-
130,000/-
130,000/-
i. Staff: NIL
Date of Appointment: NA
S.No
Expenditure Incurred
1.
Honorarium to PI (Retired
Teachers) Rs.10,000/- p.m.
2.
Project Associate Fellowship
@ Rs. 8,000/- p.m.
3.
From to
Amount
Approved
(Rs.)
Expenditure
Incurred(Rs.)
Project Fellow consolidated
salary @ Rs.6000/- p.m.
1. It is certified that the appointment(s) have been made in accordance with the
terms and conditions laid down by the Commission.
2. It as a result of check or audit objective, some irregularly is noticed, later
date, and action will be taken to refund, adjust or regularize the objected
amounts.
3. Payment @ revised rates shall be made with arrears on the availability
of additional funds.
4. It is certified that the grant of Rs1,30,000/- (Rupees One lakh Thirty
Thousand only) received from theUniversity Grants Commission under the
scheme of support for Major Research Project entitled “SYNTHESIS,
CHARACTERISATION
AND
SELECTIVITY
STUDIES
OF
CROSSLINKED POLYSTYRENE SUPPORTED SCHIFFBASES” wide
UGC letter No. MRP(S) - 285/12- 13/KLKE057/UGC- SWRO dated 29-032013 has been fully utilized for the purpose for which it was sanctioned and in
accordance with the terms and conditions laid down by the University Grants
Commission.
SIGNATURE OF PRINCIPAL
INVESTIGATOR
PRINCIPAL
UNIVERSITY GRANTS COMMISSION
BAHADUR SHAH ZAFAR MARG
NEW DELHI – 110 002
ANNEXURE VI
STATEMENT OF EXPENDITURE INCURRED ON FIELD WORK
Name of the Principal Investigator: Dr.N.B.SREEKALA
Name of the Place
visited
Four times
Car
Expenditure
Incurred
(Rs.)
2400
University Library,
Palayam
Five times
Car
4600
RRL, Pappanamcode
Three times
Car
3000
Dept. of Chemistry, Uty
of Kerala, Karyavattom
Campus
Duration of the visit
One day
Total
Mode of
Journey
10,000/-
Certified that the above expenditure is in accordance with the UGC norms for
Major Research Projects
SIGNATURE OF PRINCIPAL
INVESTIGATOR
PRINCIPAL
ANNEXURE VII
UNIVERSITY GRANTS COMMISSION
BAHADUR SHAH ZAFAR MARG
NEW DELHI – 110 002
PROFORMA FOR SUBMISSION OF INFORMATION AT THE TIME OF
SENDING THE FINAL REPORT OF THE WORK DONE ON THE
PROJECT
1. Name and address of the Principal Investigator: Dr.N.B.SREEKALA,
ASSISTANT PROFESSOR, DEPT. OF CHEMISTRY, SREE
NARAYANA COLLEGE, KARAMCODE P.O, CHATHANNUR,
KOLLAM.
2. Name and address of the Institution: SREE NARAYANA COLLEGE,
KARAMCODE P.O, CHATHANNUR, KOLLAM.
3. UGC approval no. and date: MRP(S) - 285/12- 13/KLKE057/UGC- SWRO,
Dated 29-03-2013
4. Date of implementation: 29/03/2013
5. Tenure of the project: 2 yrs.
6. Total grant allocated: 130000/7. Total grant received: 118000/8. Final expenditure: 130000/9. Title of the project: “SYNTHESIS, CHARACTERISATION AND
SELECTIVITY STUDIES OF CROSSLINKED POLYSTYRENE
SUPPORTED SCHIFFBASES”
10.Objectives of the project: Enclosure I
11.Whether objectives were achieved (GIVE DETAILS): Yes
12.Achievements from the project: A new series of Polystyrene supported Schiff
base complexes were prepared and characterised.
13.Summary of the findings: Enclosure III
(IN 500 WORDS)
14.Contribution to the society: The synthesized complexes may be utilized for
metal ion separation and need further studies. The work is presented in the
National Seminar.
(GIVE DETAILS)
15.Whether any Ph.D. enrolled/produced: No
Out of the project
16.No. of publications out of the project: One Seminar presentation and one
Poster presentation Enclosure II
(PLEASE ATTACH RE-PRINTS)
PRINCIPAL INVESTIGATOR
REGISTRAR/PRINCIPAL
No:
DATE:
CERTIFICATE
I hereby certify that the summary of the Minor Research Project (MRP(S) - 285/1213/KLKE057/UGC- SWRO, Dated 29-03-2013) done by Dr. N.B. Sreekala, Assistant
Professor, Department of Chemistry is posted in the college website and a copy of
the report is kept for reference in the college library. The title of the project is
“SYNTHESIS,
CHARACTERISATION
AND
SELECTIVITY
STUDIES
CROSSLINKED POLYSTYRENE SUPPORTED SCHIFFBASES”
PRINCIPAL
OF
ACKNOWLEDGEMENT
I express my sincere gratitude to the Principal S.N. College
Chathannur , teachers of the Chemistry Department for their support
and cooperation for the successful completion of this project work.
I also express my heartfelt thanks to University Grants Commission, for
the financial assistance towards the successful completion of the project.
Dr. N.B. SREEKALA
CONTENTS
PAGE NO.
CHAPTER I
INTRODUCTION
1-3
CHAPTER II
A BRIEF REVIEW OF METAL
CHELATION USING POLYMER
BOUND LIGANDS
4 - 13
CHAPTER III
MATERIALS AND METHODS
14 - 22
CHAPTER IV
RESULTS AND DISCUSSIONS
23 - 34
CHAPTER V
CONCLUSION
REFERENCES
35 - 36
37 - 39
CHAPTER I
INTRODUCTION
The functionalized polymers find wide use as polymeric catalysts 1 , polymeric
chelating ligands
2,3
. Anchoring chelating ligands to insoluble polymer matrix
and the reaction of these chelating resins with metal ions provide an easy route for
the synthesis of
immobilized
coordination compounds
4, 5
. Among polymer
supported metal chelates Schiff base metal chelates are important due to their
novel structural features and applications in biological processes, pre-concentration
of metal ions, catalysis etc6, 7. Polystyrene chelating resins provide an easy route
for the removal of heavy metal pollutants. Several polymer supported ligands
like porphyrins , polydentate amines, crown ethers, iminodiacetic acid, acetyl
acetone and their metal absorbing property have been reported8,9.The main
advantage of polymer supported solid phase organic reagents over their monomeric
counterparts is the ease of separation of the excess reagent and by –product from
the desired reaction product10.The attachment of reagent to the insoluble
macromolecular matrix can also solve the problems of lability, toxicity or odour
often concerned with non-polymeric low molecular weight reagents11.Moreover in
most cases, the used polymeric reagents can be regenerated.
The overall three dimensional macromolecular structure which is decided by the
chemical nature of the monomer , molecular character and extent of crosslinking
and separation of the reactive sites from the insoluble macromolecular matrix are
decisive in dictating the nature and reactivity of attached functional groups 12. In a
polymer supported ligand , the ligand function is only an infinitesimal part of
the insoluble support and subject to
a
multitude
of
structural
variations
compared to a low molecular weight ligand. This indicates a definite influence of
the nature and extent of crosslinking on the reactivity of the polymer ligand with
metal ions. Correlation between the trends of complexation
and the structural
factors characteristic of the macromolecular matrix is important in the design and
development of new and selective complexing agents for metal ions.
In polymeric ligands the polymer support creates a special local environment for
carrying out chemical reactions. The polymer backbone imposes certain steric
restrictions on the molecule diffusing through it and the micro environmental effect
can be used to influence the outcome of chemical reactions taking place in them.
The polarity of the polymer backbone may influence the reactivity of the
functional groups attached to it and also the structure of the polymer backbone
impart size and substrate selectivity13.
When a ligand function is immobilized on a polymer matrix it has got very limited
degree of translatory
and
vibratory
motion. The important factors which
govern the inter site interactions are the degree of cross linking , capacity and
distribution of functional groups, length of the attached groups and solvent used for
complexation . Increasing the crosslink density of the polymeric support decreases
the long flexibility and discourages site-site interactions as the frequency of the
crosslink points are greater. Rigid macro porous polymers generally appear to
provide an optimum compromise of high crosslink density and rigidity. This
leads to site isolation and ease of penetration of reagents.
The technique of molecular
imprinting
, to produce imprints of molecules in
synthetic polymers has received much attention in recent years .The host polymer
networks
prearrange
around
the
guest
molecule by non - covalent
interactions –electrostatic, hydrophobic and hydrogen bonding14. This host-guest
complexation chemistry finds application in the areas of chromatographic
separations, resolution of racemic mixtures and in the design of metal ion specific
polymers15. Systems with metal ion as template are useful a sorbents
with
enhanced specificity .
The
present study is
concerned with the synthesis , characterization of
metal complexes of various Schiff base moieties attached to polystyrene support
with a view to analyzing the recyclability and specificity of the ligands.
CHAPTER II
A BRIEF REVIEW OF METAL CHELATION USING POLYMER
BOUND LIGANDS
In recent years polymer metal complexes have been of interest to many
chemists because of their versatile application in many fields like nuclear
chemistry, metal ion separation, pollution control, industrial processes,
hydrometallurgy, polymer drug grafts etc. attachment of multidentate ligand to an
insoluble polymeric support is a common technique utilized for the preparation of
selective ion exchange resins capable of separation and purification of metal ions.
Recent discoveries in coordination complexes show that the economic potentials
and advantages are more if these low molecular coordination complexes are
heterogeneous rather than homogeneous. The preparation of insoluble cross-linked
polymer backbone and chemical modification to enhance the reactivity of the
polymer ligand are main aims of the several researchers. Transition metal chelates
derived from poly-Schiff bases have occupied a central position in the
development of coordination chemistry of polychelates16.
In this review, an attempt is made to discuss the different polymeric supports,
design of ligands, various structural parameters that affect metal chelation and the
methods available for the characterization of ligands and metal complexes.
The reactivity of the polymeric reagent is influenced by the nature of solvents and
reagents to which the polymer is subjected during the course of its
functionalization and subsequent application. It also depends on the chemical
behavior of the support. The selection of a suitable support is the most crucial
factor in the synthesis of a polymeric reagent. One of the main difficulties
associated with the crosslinked polymeric reagents is the non-equivalence of
reactive groups attached to polymer net work17.
The attachment of functional groups into polymeric support is done by direct
polymerization and copolymerization of monomers containing desired functional
groups or chemical modification of a preformed polymer. Various types of
chelating ligands have been incorporated into polymer backbone which are capable
of sorbing metal ions from solutions18.
A large number of chelating ligands are known for various metal ions. To obtain a
highly selective and strong ligand for a target metal ion an effective way is to
create coordination sphere with near optimum geometry by varying the spacers
connecting ligand sites19.
I.
Macromolecular Structural Parameters affecting Chelation
The efficiency of complex formation of a macromolecular ligand is influenced not
only by the character of the functional group but also by the distribution along the
polymer chain. The different structural parameters of a polymer supported ligand
that determine its complexing power are nature and extent of crosslinking , the
distance of functional groups from the backbone , the interaction between the
functional groups , micro environmental effect , etc.
1. Nature and extent of cross linking :
The complexing characteristics of polymeric ligands are very much influenced by
the degree of crosslinking. A high degree of crosslinking results in a low metal ion
intake and a lower stability of the resulting metal complex by making the polymer
chain more rigid. In the copper complexes of poly ( 4- vinyl pyridine ) with 4-6
moles of
DVB crosslinks a conversion of planar coordination centers to
tetrahedral ones occur towards high crosslinking20.These changes in
stereo
structure arise from an increasing steric hindrance to complex formation with
macromolecules.
The complexing ability of a polymeric ligand depends on the hydrophilic nature
of the macromolecular support.
For example, in the complexation of
polyacrylamide supported amines and dithiocarbamates with DVB, NN’-MBA and
TEGDA crosslinks, the complexation characteristics vary with the molecular
character and extent of crosslinking in the polymer matrix21.The hydrophilic
TEGDA crosslinked system has higher complexing ability than the NN’-MBA and
DVB crosslinked systems.
A new series of polytetrahydrofuran (PTHF)
crosslinked polystyrene resins were prepared for solid phase organic synthesis.
The objective of incorporating PTHF into the polymers was to slightly increase the
overall polarity of the polymer and thus render the resins more organic solventlike. It was found that these resins swelled to a much greater extent than do DVBPS resins22.
The solvent has a significant effect on the chemical reactivity of the
anchored species. In the case of crosslinked polymers which are macroscopically
insoluble in almost all the solvents, by absorbing considerable amount of a suitable
solvent, the crosslinked network can expand greatly.
But the crosslink ratio
controls the behaviour of a resin in contact with a solvent and is inversely
proportional to the degree of swelling23.
With increasing polarity of the support, the extent of complexation is
increased. The metal intake by polymeric ligands are varied by the incorporation
of the crosslinking agents, which differ in their polarity and flexibility24. When the
polarity of the solvent used and that of the polymer backbone match, the yields of
products were found to be maximum.
2. Effect of spacer groups:
The complexing power of a polymeric ligand also depends on the
arrangement of functional groups relative to the main chain. The shorter the
distance between them, the lower is the efficiency of complex formation because
of steric hindrance. The polymer backbone imposes some steric restrictions on the
bound species causing decreased reactivity. If the reactive residue is kept at proper
distance from the polymer backbone by the interposition of the spacer grouping
between the rigid polymer matrix and the reactive site, the steric factor is reduced
and hence the reactivity increases.
An increased sorption capacity was obtained when the functional groups are
separated from the polymer backbone by a flexible spacer arm. However, the
introduction of a spacer group reduces the selectivity of the ligand.
To obtain a highly selective and strong ligand for a target metal ion, an
effective way is to create coordination sphere with near optimum geometry by
varying the spacers connecting ligating sites. If the ligands of a preassembled
complex are crosslinked with a spacer that allows conservation of the geometry of
the coordination sphere, an effective multidentate sequestering agent can be
obtained. In this regard, polyethylenimine (PEI) can be employed as a spacer to
crosslink ligating sites present in a preassembled metal complex. This is due to the
structure of PEI containing many branches and the availability of many amine
nitrogens, which helps in conserving the geometry of the coordination sphere of
the preassembled complex by crosslinkage.
3. Micro environmental effects:
In polymeric ligands the polymer support creates a special local environment for
carrying out chemical reactions. The polymer backbone imposes certain steric
restrictions on the molecules diffusing through it and the microenvironmental
effect can be used to influence the outcome of chemical reactions taking place in
them. The polarity of the polymer backbone may influence the reactivity of the
functional groups attached to it and also the structure of the polymer backbone
impart size and substrate selectivity25.
The extent of complexation of DVB crosslinked polyacrylamide is found to
be higher than the DVB crosslinked polystyrene resins.
The complexation
characteristics of crosslinked polyacrylamides were found to be increased with
increasing crosslinking. Here the crosslinking agent decreased the hydrophobic
nature and thus a better hydrophilic-hydrophobic balance is achieved, thereby
making the active sites more amenable to the substrates.
4. Intersite interactions and site isolation:
When a ligand function is immobilised on a polymer matrix, in the sense
that it has got very limited degree of translatory and vibratory motion, their
interaction is limited substantially. The important factors which govern the intersite
interactions are the degree of crosslinking, capacity and distribution of functional
groups, length of the attached group and the solvent employed for the
complexation. Increasing the crosslink density of the polymeric support decreases
the long flexibility and discourages site-site interactions as the frequency of the
crosslink points are greater. Rigid macroporous polymers generally appear to
provide an optimum compromise of high crosslink density and rigidity. This leads
to site isolation and ease of penetration of reagents.
When two functional groups are attached to the polymer chain, interactions
between the groups can occur. It was noticed that in solution of a copolymer of
styrene and methacrylic acid, the extent of hydrogen bonding was independent of
the polymer concentration showing that intrapolymeric interaction is taking place.
In the case of polymer bound chelates, there is the possibility of isolation of
coordination centers with respect to each other.
II.
Characterisation of Chelating Resins and their Metal Complexes
The characterisation of polymeric chelating resins and their metal complexes
is of great importance. Both physical and chemical techniques are used for the
characterisation. The efficiency of a chelating sorbent depends on the type of
functional groups, nature of the polymeric matrix and also on the conditions of
sorption. The coordination behaviour of the functional groups towards metal
ions and the geometry around the metal ion are studied by spectroscopic
method such as IR, NMR, ESR, X-ray, ORD or CD analysis26 -28 .
Elemental analysis is used for the detection and estimation of elements
like nitrogen, sulphur, phosphorous and halogens. Thermal studies (TG,DTG and
DSC) have been used to study the thermal decomposition behaviour of the
resins
and
their
complexes. Titrimetric methods are usually used for the
estimation of metal ions.
I.
Analytical Methods:
Various analytical methods are used to determine the parameters such
as
density, grain size, water
content,
ash
content, capacity, distribution
coefficient ,selectivity coefficient, etc. The capacity of a metal ion sorbent is
defined as the number of counter ion equivalents in a specified amount of
the material29.
II.
Physico-Chemical Methods:
A number of physico-chemical methods mainly based on spectral and
magnetic properties of chelating resins and their metal complexes are used for
characterising these polymeric compound.
a. Spectroscopic methods:
i. Infrared spectroscopy
Infrared spectroscopy provides an excellent tool for characterising
chelating resins and to locate the coordinating sites in these resins. The IR
absorptions by a ligand are usually shifted by complex formation with metal
ions115. It has been qualitatively used to show the presence
of certain
functional groups in a polymer or to determine the extent to which chemical
transformation
has taken place. IR spectra of polymers contain hydroxyl or
carbonyl group can provide additional information about the extent of
hydrogen bonding in the resin. In the case of multidentate ligands IR spectrum
is used to find which groups take part in complexation 30. FTIR spectroscopy
has been extensively used for the study of crosslinked polymers and their metal
complexes.
ii.
Nuclear Magnetic Resonance spectroscopy
1
H, 13C and 19F NMR spectroscopy all have been used in monitoring solid
phase reactions. However the application of NMR in the structural analysis of
polymers and complexes are limited due to the low solubility of the samples
and broadening of the spectra. In general, complex formation with metal ions
lead to shifts, splitting or broadening of the peaks due to ligand molecules. In the
absence of anion effect, a downward shift
electronegativity
is expected due to the increased
of the donor atoms of the ligand31, 32. However there will be
great improvements in 13C NMR technique to study the crosslinked polymers33.
iii.
ESR Spectroscopy
Application of ESR spectroscopy
for monitoring
the degree of
functionalisation of a polymer is limited primarily because ESR active groups
are mostly used as probes rather than as reactive functionalities. There are report
on the use of ESR to estimate the proximity of titanium groups in a titanocene
polymer34.
ESR
spectroscopy
is being
increasingly
used to
coordination structure of polymer complexes. The interaction
spin of the central
metal
study
the
between the
ion and the coordinated ligand decide the
absorption pattern and its ‘g’ value which in turn can be used to study the
metal-ligand bond.
iv.
Other Methods
Electronic spectra of metal complexes are generally used to study the
geometry around the transition metal ion in the complex. The number and
position of bands give an idea about the geometry of the complex.
The diffuse reflectance electronic spectra
provide an accurate and simple
method for determining the geometry around the transition metal ions.
Mössbauer spectroscopy has been found useful for the study of iron and
some lanthanide complexes of polymeric chelating sorbents35 .
III.
Magnetic Susceptibility Measurements
Measurement of the magnetic susceptibility forms an integral part of
the characterisation of metal complexes. It gives an idea of the geometry of the
complexes. For example, Ni (II) complexes are diamagnetic if the
geometry
around the Ni (II) ion is square planar. On the other hand, it is paramagnetic if
the geometry is either tetrahedral or octahedral. Magnetic moment
values also
give clear indication of the presence of metal-metal bond in the complex.
Scope of the Present Investigation:
Polymer supported metal complexes find wide applications in different
fields of science and technology. Anchoring of chelating ligands to insoluble
polymer matrix and the
reaction of these chelating resins with metal ions
provide
for
an easy route
the
synthesis
of
immobilised
coordination
compounds .The Schiff bases are an important class of ligands which have
played significant role in coordination chemistry . Although a large number of
non-Schiff base ligands like diethyldithiocarbamate, oxine,
have
etc
been immobilised to polymer supports, only few Schiff bases have
been anchored
highly
-diketones,
selective
to polymer matrix. Thus there is a further need to develop
chelating
resins
with
high
capacity
and
reasonable
mechanical strength .
The structural study
of these polymeric metal complexes seems
interesting and useful in view of the numerous applications that such resins
find in organic synthesis, analytical studies , catalytic reactions, biological
systems, etc. In the present study polystyrene bound Schiff bases are prepared and
studied their metal intake capacity.
CHAPTER III
EXPERIMENTAL
MATERIALS AND METHODS
All the reagents and solvents used were of analytical grade. The polymer
supports used in all the experiments were DVB crosslinked polystyrene.
Merrifield resin (Fluka) is used as such. Metal salt solutions were prepared in
doubly distilled water. The IR spectra were recorded on a Perkin Elmer FT-IR
Paragon 1000 spectrophotometer (4000–400 cm-1). The reflectance spectra were
recorded on a Perkin Elmer Lambda 20 UV-Vis spectrophotometer. ESR spectra
were measured on a Varian E112X-Q band ESR spectrometer. The magnetic
susceptibilities were determined on a Gouy balance using Hg[Co(NCS)4] as the
calibrant. Thermal analyses were done on a Du Pont 2000 thermobalance in air at
a heating rate of 10oC/min. Standard volumetric and colourimetric methods were
employed to determine the metal ion concentration.
I.
Preparation of Aminomethylated Polystyrene36
A mixture of chloromethyl polystyrene (2% DVB crosslonked, 0.7 m mol
Cl/g, 10g), hexamethylenetetramine (0.2g, 1.4 mmol) and KI (0.21g, 1.4mmol) in
DMF (150mL) was heated with stirring at 100ºC for 10 h. The suspension was
poured into water and stirred for 30 minutes. The resin was filtered, washed with 6
N HCl and water. It was then stirred with a solution of NaOH (1.6g, 100mL) for 2
h, filtered washed several times with water and methanol and dried under vacuum
to afford the aminomethyl resin. The amino group capacity of the resin was 3.4
mmol/g.
1. HEXAMETHYLENE TETRAMINE
CH2 Cl
2. EtOH/HCl
CH2 NH
2
3. NaOH
Fig 1. Preparation of aminomethylated polystyrene.
II.
Preparation of Azo Derivatives of Substituted Benzaldehydes and
Naphthaldehyde
Azo derivatives of substituted benzaldehydes and naphthaldehyde were used
for the preparation of the Schiff bases. Azo substitution was done as follows: The
amino compound (0.01 mol) was dissolved in dilute hydrochloric acid (125 mL,
0.01 M), cooled to 4-5oC and 5% aqueous solution of NaNO2 was added drop by
drop until there was no excess in solution (10mL).
The phenolic compound
(0.01mol) was dissolved in 10mL of 5% NaOH solution and added to the
diazotised amino compound. To this mixture 20 mL of 0.1 M HCl was added to
give a solid product which was filtered, washed with water and dried in vacuum
over CaCl2.The various aldehydes used in the synthesis are given in Fig.(2)
R2
R3
CHO
R6
R4
R5
R2
R4
R5
H
R2
R4
R5
H
R3
R3
Cl
N
N
R6
OH
N
N
R6
OH
N
R6
OH
CH3
R2
R4
R5
H
R3
N
R4
R5
R6
R3
R7
R2
CHO R8
R3
R4
R5
R6
R7
R8
H
R2
OH
R3
R5
R6
R7
R8
R2
H
OH
N
R4
N
Fig 2. Azo derivatives of substituted benzaldehyde and naphthaldehyde
III.
Preparation of Polystyrene anchored Ligands
It was prepared from Aminomethylated polystyrene. Aminomethylated PS
(3g) was suspended in DMF (40 ml) for 45 minutes. It was refluxed with azo
derivatives for 10 hours. The dark coloured compound obtained was filtered,
washed with DMF, ethanol and dried in vacuum. The different resins are given in
Fig. (3)
R3
R4
R2
R4
R5
R3
NH2
N
+
R6
R2
R6
H
CHO
Resin (1)
R3
R4
R6
H
R6
OH
R5
N
N
N
N
Cl
Resin (2)
R3
R4
R6
H
R6
OH
R5
CH3
R3
R4
R5
C
R6
H
R6
OH
R5
N
N
Resin (3)
R4
R4
R5
R6
R3
R6
R3
+
NH2
R5
R2
R2
CHO R
8
N
R7
CH
R8
R7
Resin (4)
R3
R4
R5
R6
R7
R8
H
R2
OH
R4
OH
Resin (5)
R3
R5
R6
R7
R8
H
R2
N
N
Fig 3.The Resins obtained from substituted benzaldehyde and naphthaldehyde
IV.
Chelation Experiment with Metal ions
The efficiency of chelation of the polymeric Schiff bases was checked with various
metal ions.
Preliminary studies to correlate the extent of complexation with
concentration of metal ions in solution and the duration of equilibration of the resin
with the metal ions were carried out. The optimum conditions obtained from these
studies were used to design further experimentation and used for the present
complexation studies. Similar concentration ranges as used here were reported in
complexation studies of resins with metal ions37. About 300 mg of the resin was
accurately weighed and shaken with a known excess of aqueous solutions of the
chlorides of Mn(II), Fe(III), Co(II), Ni(II) and the nitrates of Cu(II) and Zn(II) ions
(0.02 M, 40 mL) for 24 h. The complexes formed were separated by filtration.
Standard volumetric and colourimetric techniques were used for determining the
concentration of the excess metal ions. Co(II), Ni(II) and Zn(II) were determined
by complexometry. Mn(II) and Fe(III) were determined colourimetrically38. The
complexation of the Schiff bases with metal ions was conducted in the pH range
2.0–6.0. The pH was adjusted to 3.5–6.0 using acetic acid/ammonium acetate
buffer. The pH values below 3.5 were adjusted by adding dilute HCl.
V.
Determination of residual metal ion concentration
1. Estimation of iron
A definite volume of made up iron filtrate (2mL) was taken in a 100mL
standard flask. Concentrated HNO3 (2mL) was added. The colour was developed
by adding potassium thiocyanate solution (5mL, 2M). The solution was made up to
100mL. The absorbance was measured in a colourimeter at 480 nm (blue–green
filter). The concentration of the solution was determined by comparison with
values in a reference curve.
2. Estimation of Cobalt
Definite volume (20 mL) of made up cobalt ion solution was pipetted into a
clean conical flask. It was diluted to 50 mL with distilled water. Three drops of
xylenol orange indicator ( 0.5 g in 100 mL distilled water) was added followed by
very dilute sulphuric acid drop by drop until the colour changed from red to
yellow. Powdered hexamine was added with shaking until the deep colour was
restored (pH=6). The solution was warmed to 40ºC and was titrated with standard
EDTA until the colour changed from red to yellow orange.
3. Estimation of Nickel
A back titration process was adopted, definite volume (20 mL) of made up
nickel ion filtrate was mixed known excess (30 mL) of standard EDTA (0.01M).
The solution was diluted to 200 mL with de-ionised water. Aqueous NH3- NH4Cl
buffer (4 mL, pH=10) was added. Eriochrome black T indicator (30-40 mg) was
added. The excess EDTA remaining was titrated with standard 0.01 M Zn 2+
solution until the colour changed from blue to wine red.
4. Estimation of copper
Definite volume (20mL) of made up copper ion filtrate was pipetted into an
iodine flask. The mineral acid remaining, if any was neutralised by adding diluted
solution of ammonium hydroxide in drops until a faint permanent precipitate was
formed. The precipitate was dissolved in very dilute acetic acid (1or2 drops). KI
solution (10mL, 10%) was added. The liberated iodine was titrated by using starch
as indicator. The end point was the disappearance of blue colour. 10mL of 10%
ammonium thiocyanate solution was added towards the end of the titration to
desorb the iodine absorbed by cuprous iodide.
5. Estimation of Manganese
Define volume of made up filtrate was pipetted out. Potassium per iodate
was added to the above solution stirred well over a boiling water bath for about 20
minutes. The solution developed the colour of potassium permanganate. It was left
aside for some time for full development of colour. The absorbance of the pink
solution was measured at 545 nm. A calibration curve was constructed using
standard permanganate solution. The manganese content was read from the
calibration curve.
6. Estimation of Zinc
Definite volume of residual Zn2+ solution (20mL) was pipetted into a conical
flask. The solution was diluted to 100mL with de-ionised water. Aqueous NH3NH4Cl buffer (2mL, pH=10) was added. The solution was titrated against EDTA
solution (0.01M) until colour changes from red wine to blue.
VI.
Effect of pH on complexation
In order to study the effect of pH on the extent of complexation, the
experiments were conducted at various pH values in aqueous medium. The effect
was noticed in the pH range 2-6. For maintaining the pH between 2-3, dilute HCl
was used and for adjusting the pH in the range 3-6 acetic acid–sodium acetate
buffer was used. The metal ion solution (40mL each) were preconditioned at the
desired pH and the polymeric ligands (500 mg) were equilibrated for a period of 18
h. Standard volumetric and colourimetric method were employed to determine the
metal ion concentrations.
VII.
Magnetic Moment Measurement
Magnetic moment was measured at room temperature on a simple Gouy
balance. In this technique, a glass tube filled upto a certain height with magnetic
sample was suspended from an arm of sensitive balance such that, the bottom part
was in a strong magnetic field while the top part was in a zero field. The whole set
up was housed inside a drought free enclosure. An electromagnet giving a constant
magnetic field in the range 5,000-10,000 Gauss was used. The magnetic
susceptibility of the complexes was determined at room temperature.
The Gouy tube was first weighed without and then with magnetic field on. It
was then filled with distilled water and weight was taken in the same way. Then
the calibrated, Hg [Co (NSC) 4] was filled with the magnetic samples and weight
taken. The effective magnetic moments were calculated from the molar
susceptibility using the relation, μeff = 2.84(XM.T)
susceptibility and T is the absolute temperature.
1/2
. Where XM is the molar
CHAPTER IV
RESULTS & DISCUSSIONS
The efficiency of chelation of polymeric Schiff bases were checked with
Mn(II),Fe(III), Co(II), Ni(II),Cu(II) and Zn(II) ions.
Preliminary studies to correlate the extent of complexation with concentration of
metal ions in solution and the duration of equilibration of the resin with the metal
ions were carried out. The optimum conditions obtained from these studies were
used to design further experimentation and used for the present complexation
studies.
The complexation of the Schiff bases with metal ions was conducted in
the pH range 2.0–6.0.
The pH was adjusted to 3.5–6.0 using acetic
acid/ammonium acetate buffer. The pH values below 3.5 were adjusted by adding
dilute HCl.
The uptake of metal ions by the resins at equilibrium follows approximately
the order Fe(III) > Cu(II) > Ni(II) ~ Mn(II) ~ Co(II) > Zn(II). The variation in
Mn(II), Ni(II) and Co(II) is too small (±0.1 meq. /g) to warrant any critical
conclusions. However, considering the larger charge/radius ratio of Mn(II), when
compared with Zn(II), the higher affinity for Mn(II) than Zn(II) is unexpected.
With simple ligands the affinity for a particular metal ion in complexes increases
with the charge/radius ratios. For the different resins that have substituted
azobenzenes attached to the phenyl ring, extent of sorption decreased as the
bulkiness of the group attached to the azobenzene increased.
Amount of metal ions complexed by the ligands
Polymeric
Schiff base
ligands
Metal ion intake capacity (m eq/g)
Mn (II)
1
2
3
4
5
1.39
1.18
1.09
0.99
0.81
Fe(III)
1.78
1.65
1.59
1.36
1.13
Co(II)
1.25
1.13
1.01
0.84
0.72
Ni(II)
1.26
1.12
1.02
0.88
0.79
Cu(II)
Zn(II)
1.52
1.28
1.21
0.97
0.92
1.06
0.95
0.79
0.69
0.54
During complex formation, there may be changes in the conformation of the
polymeric ligand. The amount of loading of macroligand with metal ion is more
significant for polymer complexes in comparision to the metal ligand ratio used for
soluble low molecular weight metal complexes. The concept of binding at a
specific site is insignificant for crosslinked polymer.
I.
Effect of pH on chelation
The complexation of ligands with metal ions was conducted in the pH range
of 2.0-6.0. In the case of Fe(III) and Cu(II), a slight precipitation occurred above
pH values 3.5 and 5.5 respectively. It was observed that sorption first increased,
reached the optimum values and then decreased. The optimum pH for metal ion
uptake was found to around 4.0 for Mn (II), 2.0-3.0 for Fe(III), 5.0 for Co(II),
Ni(II) and Cu(II) and 3.0-4.0 for Zn(II)
Metal ion uptake by resins at the pH of maximum uptake.
Resin
Mn(II)
1.48 (4)
1.27 (4)
1.09 (4)
1.05 (4)
0.92 (4)
1
2
3
4
5
Metal ion uptake in meg./g of resin (pH)
Fe(III)
Co(II)
Ni(II)
Cu(II)
1.92 (3) 1.17 (5) 1.25 (4,5) 1.27 (4,5)
1.61 (3) 1.07 (4) 1.12 (4)
1.14 (4)
1.54 (2) 1.02 (5) 1.05 (5)
1.24 (5)
1.38 (3) 0.84 (5) 0.97 (5)
1.12 (5)
1.21 (3) 0.71 (5) 0.76 (5)
0.91 (5)
Zn(II)
0.58 (4)
0.47 (4)
0.76 (3)
0.64 (4)
0.52 (4)
Metal ion uptake was highest for resin (1). All other resins showed lesser
metal ion uptake and the extent of sorption decreased as the bulkiness of the group
attached to the azobenzene increased.
II.
Characterisation
Both physical and instrumental methods were used for characterising the
ligands and complexes. Physical measurements mainly involved magnetic
susceptibility measurements. Instrumental analysis mainly involved UV/VIS,IR,
and ESR spectral methods. The structure and geometry of the polymer metal
complexes are largely determined by the microenvironment of the polymer
domain39.
1. Spectral and Magnetic Properties:
a. Infrared Spectra:
The IR spectra of the ligands showed a well-defined band around 1600 cm-1
characteristic of the azomethine group. In all the complexes it shifts to lower
energy by 20-25 cm-1 which indicates nitrogen coordination of the azomethine
group. In the complexes a new band was observed around 550-570 cm-1, which is
assigned to the M-N frequency133. All the ligands showed a broad band around
3400 cm-1 assigned to ν (OH) which disappears in the complexes. The involvement
of deprotonated oxygen in coordination is supported by the presence of bands in
the region of 470-530cm-1, which are assigned to M-O frequency40. In all of the
complexes, a broad band was observed around 3300- 3400 cm-1 due to coordinated
water. A band observed around 1450 cm-1 in the ligands is assigned ν (N=N). This
band appeared in all the complexes in the same region except in resin (I). Some of
the important spectral values are given in the table below.
Tentative Assignment of some Selected Infrared
Frequencies (cm-1)
Compound
(CN)
(OH)
(N=N) (MN) (MO) (H2O)
Resin (1)
1608 m
3410 s
-
-
Mn(II)
1585 m
-
-
562 w
Fe(III)
1580 m
-
-
560 m 507 m 3338 br
Co(II)
1584 m
-
-
564 w
512 w 3358 br
Ni(II)
1582 m
-
-
559 w
513 w 3364 br
Cu(II)
1580 m
-
-
560 w
512 w 3347 br
Zn(II)
1579 m
-
-
563 w
526 w 3339 br
Resin (2)
1601 m
3402 s
1448 w
-
Mn(II)
1581 m
-
1446 w 564 w
Fe(III)
1579 m
-
1445 w 567 m 515 m 3379 br
Co(II)
1582 m
-
1447 w 562 w
516 w 3358 br
Ni(II)
1580 m
-
1448 w 560 w
524 w 3366 br
Cu(II)
1578 m
-
1443 w 558 w
508 w 3342 br
Zn(II)
1579 m
-
1447 w 565 w
527w
3364 br
Resin (3)
1604 m
3405 s
-
-
Mn(II)
1584 m
1442 w 558 w
Fe(III)
1582 m
1446 w 567 m 506 m 3350 br
Co(II)
1584 m
1440 w 559 w 504 m 3355 br
Ni(II)
1578 m
1445 w 562 w 512 m 3378 br
1445 w
-
-
-
504 w 3377 br
-
-
508 w 3376 br
518 w 3375 br
Cu(II)
1573 m
1444 w 560 w
524 w 3365 br
Zn(II)
1576 m
1443 w 556 w
525 w 3340 br
Resin (4)
1610 m
Mn(II)
1588 m
1446 w 569 w
Fe(III)
1592 m
1442 w 558 m 510 m 3374 br
Co(II)
1587 m
1440 w 562 m 522 w 3375 br
Ni(II)
1581 m
1443 w 557 m 528 w 3382 br
Cu(II)
1593 m
1445 w 558 w
512 w 3340 br
Zn(II)
1585 m
-
1444 w 558 w
506 w 3335 br
Resin (5)
1609 m
3408 s
Mn(II)
1585 m
-
1453 w 560 w
Fe(III)
1582 m
-
1451 w 568 m 498 m 3380 br
Co(II)
1593 m
-
1448 w 555 m 503 m 3365 br
Ni(II)
1590 m
-
1449 w 559 m 481 w 3371 br
Cu(II)
1592 m
-
1447 w 562 m 497 w 3363 br
Zn(II)
1586 m
-
1452 w 559 w
3401 s
1446 w
-
1450 w
-
-
-
504 w 3332 br
-
-
501 w 3380 br
508 w 3365 br
m = medium, w = weak, br = broad.
b. Electronic spectra:
The reflectance spectra of the polymer- anchored Fe(III) complexes showed a band
around 19,000 cm-1 which could be assigned to the
6
A1g  4T1g transition in an
octahedral environment. The magnetic moment of about 5.8 B.M also supports
high spin octahedral Fe(III) complexes. The Co(II) complexes show magnetic
moment values of about 4.4 BM, which is close to a tetrahedral geometry. These
complexes showed a band around 18000 cm-1 which could be assigned to the 4A2g
 4T1g (P) transition. This gave a blue colour to the Co(II) complex of resin (1).
Since these resins (2)-(5) themselves are intensely coloured the colour changes
occurring on complexation of Co(II) with these resins could not be detected.
However, the band around 18,000 cm-1 was observed in all the Co(II) complexes
and, hence, a tetrahedral geometry was assumed for the Co(II) complexes.
The Ni(II) complexes are paramagnetic indicating that the geometry around
Ni(II) was either tetrahedral or octahedral. But the observed magnetic moments of
about 3.0 BM correspond to that of an octahedral geometry41. Octahedral Ni(II)
complexes give three transitions in the visible region40. In the present study two
bands are obtained around 11,300 and 19,000 cm-1. The third band was
inaccessible due to instrumental limitations. Hence an octahedral structure was
assigned to the Ni(II) complexes.
The Cu(II) complexes gave an asymmetric band around 14,500 cm-1. The
copper complexes of resin (1) was blue while any colour change in the other Schiff
base complexes of Cu(II) could not be ascertained due to the intense colours of the
Schiff bases themselves. The asymmetry of the band is due to the Jahn-Teller
effect in an octahedral environment. The observed magnetic moments of about 1.9
B.M indicated that the copper complexes are magnetically dilute. These datas are
given in the table. Because these complexes are crosslinked polymers and
insoluble, X-ray structural studies are impracticable. Structural deductions from
electronic spectra and magnetic moments are therefore tentative.
Electronic Spectral, Magnetic Susceptibility and Electron Spin Resonance
Data of some of the Metal Complexes of the Resins
Band Maxima (cm-1)
Resin Metal ion
complexed
(1)

ESR Data
Band 1 Assignment Band 2 Assignment g
g
(B.M)
Mn(II)
5.84
Fe(III)
5.60 18,900 6A1g  4T1g
Co(II)
4.38 18,000
4
A2g 
T1g(P)
4
Ni(II)
2.89 11,300 3A2g  3T2g 19,100
3
A2g 
T1g(F)
3
(2)
dd
Cu(II)
1.84 14,400
Mn(II)
5.79
Fe(III)
5.72 19,200 6A1g  4T1g
Co(II)
4.43 18,100
4
2.24 2.03
A2g 
T1g(P)
4
Ni(II)
3.12 11,300 3A2g  3T2g 19,100
3
A2g 
T1g(F)
3
(3)
dd
Cu(II)
1.89 14,600
Mn(II)
5.73
Fe(III)
5.48 19,000 6A1g  4T1g
Co(II)
4.08 18,000
4
2.23 2.06
A2g 
T1g(P)
4
Ni(II)
3.12 11,300 3A2g  3T2g 19,100
3
A2g 
T1g(F)
3
Cu(II)
1.90 14,500
dd
2.21 2.01
(4)
Mn(II)
5.82
Fe(III)
5.32 19,100 6A1g  4T1g
Co(II)
4.41 18,100
4
A2g 
T1g(P)
4
Ni(II)
3.07 11,200 3A2g  3T2g 19,100
3
A2g 
T1g(F)
3
(5)
dd
Cu(II)
1.89 14,300
Mn(II)
5.78
Fe(III)
5.38 18,900 6A1g  4T1g
Co(II)
4.01 17,900
Ni(II)
3.08 11,200 3A2g  3T2g 18,800
2.24 2.02
A2g 
4
T1g(P)
4
3
A2g 
T1g(F)
3
Cu(II)
1.91 14,400
dd
2.23 2.01
c. Electron Spin Resonance Spectra:
The ESR spectra obtained for the Cu(II) complexes are characteristic of
Cu(II) ion in an axial ligand field symmetry. The hyperfine splitting is seen in the
parallel component and not in the perpendicular component. Measured g || values
were in the range 2.25–2.31 while the g values were between 2.01–2.04. The
order g|| > g > ge (ge = 2.00023) observed for the complexes showed that the
unpaired electron was localised in the dx2-y2 orbital and that the spectrum was
characteristic of axial symmetry.
2. Thermal Studies
Thermal decomposition studies of Schiff bases and complexes were done
and kinetic parameters like energy of activation, pre-exponential factors and
entropy values were calculated using the Coats-Redfern equation42. The ligands
and complexes were stable up to about 127oC. The weight loss at this stage
corresponded to the loss of adhered water molecules. All the compounds showed a
two-stage decomposition profile. For the first stage the energy of activation was in
the range of 30–50 kJ mol-1, while for the second stage it was at 240–280 kJ mol-1.
The S values for the first stage was found to be negative (-145 to -220 JK-1 mol-1)
while for the second stage it is positive (60–74 JK-1 mol-1). The negative values
obtained for S in the first stage indicated that the transition state was more
ordered than the reactants and the positive values of the entropy of activation in the
second stage indicated the less ordered nature of the transition state.
Kinetic Parameters for the Thermal Decomposition of the Resins and the
Metal Complexes
Decomposition
Resin
Stages
I Dec.
Temp.(oC)
E/kJ mol
163
(1)
216
219
225
238
205
42.46 45.65 32.08 39.57 39.52 47.34 48.92
187.50 152.09 172.54 146.77 184.54 208.59 217.30
-S/JK mol
-1
II Dec.
Temp.(oC)
339
421
416
424
429
419
408
247.04 279.54 246.48 255.42 264.54 273.79 245.42
-1
S/JK mol
-1
212
-1
-1
E/kJ mol
Metal Complexes
Mn(II) Fe(III) Co(II) Ni(II) Cu(II) Zn(II)
68.77 71.25 72.59 67.76 63.50 72.08 71.56
-1
I Dec.
Temp.(oC)
E/kJ mol
172
(2)
243
248
251
232
229
211
41.38 39.05 42.53 45.30 39.52 38.07 44.42
-1
148.34 178.56 163.66 159.52 147.30 192.62 204.49
-S/JK-1mol-1
II Dec.
Temp.(oC)
E/kJ mol
345
447
451
442
438
429
411
258.30 246.40 259.54 268.36 273.75 269.08 248.40
-1
60.34 70.91 68.08 67.10 71.18 67.52 61.40
S/JK-1mol-1
I Dec.
Temp.(oC)
E/kJ mol
187
(3)
212
230
225
210
30.52 36.41 29.07 40.01 45.82 42.82 45.58
208.04 189.25 205.56 212.31 174.21 180.04 170.52
-S/JK mol
-1
II Dec.
Temp.(oC)
338
S/JK mol
-1
449
450
443
418
435
415
268.28 265.35 271.84 241.69 248.97 272.55 265.22
E/kJ mol-1
56.85 61.04 65.48 62.56 64.54 70.38 70.89
-1
I Dec.
Temp.(oC)
164
(4)
211
217
218
224
235
204
42.56 45.05 28.12 35.58 38.52 47.35 47.92
-1
185.5 150.08 173.44 145.78 182.54 206.54 216.35
-1
-S/JK mol
-1
II Dec.
Temp.(oC)
E/kJ mol
250
-1
-1
E/kJ mol
240
340
420
418
425
410
415
406
245.08 275.42 244.59 263.54 274.79 270.52 240.52
-1
S/JK-1mol-1
69.78 70.25 65.76 60.50 70.05 70.68 70.76
I Dec.
Temp.(oC)
E/kJ mol
173
(5)
240
245
250
230
228
210
39.42 38.04 40.25 44.38 38.44 37.06 43.72
-1
147.08 176.56 160.65 156.92 146.26 191.65 204.85
-S/JK-1mol-1
II Dec.
Temp.(oC)
E/kJ mol
341
444
450
441
435
428
412
250.58 245.28 258.52 265.36 271.65 265.52 245.40
-1
61.39 69.35 68.09 66.10 70.28 66.02 62.57
S/JK-1mol-1
Dec. Temp. = Decomposition temperature
3. Recyclability and specificity of complexed resins43
The recyclability of the Cu (II) complexes were investigated after decomplexing
with dilute acid. The resin can be recycled several times without reduction in
capacity. The Cu(II) desorbed resins on recycling when treated with Co(II), Ni(II),
Cu(II) and Zn(II) ions selectively took Cu(II) in the presence of other metal ions.
It is possible that the “pockets” left by the Cu (II) ions may not be suited for other
metal ions. This is due to the geometry and size of the Cu (II) desorbed resins are
more apt for the Cu (II) ions than the Co (II), Ni (II) and Zn (II) ions. This
indicates the selectivity of the conformational prearrangement of the
macromolecules and shows the important role played by fixing a certain location
of functional groups in the chemical reaction of polymers.
CHAPTER V
CONCLUSION
Macromolecules have effective utilisation in many areas of scientific
endeavour. The study of macromolecules received greater importance since
Merrifield demonstrated their use in polymer synthesis. Functionalised polymers
find numerous applications in the various fields of science and technology. Active
research has been carried out on the reactive functional polymers which
participates in metal ion complexation, due to their wide application in catalytic
activities, separation of metal ions and so on. Thus their synthesis and
characterisation have got tremendous importance.
A new series of chelating resins were prepared by anchoring Schiff base
moieties on lightly crosslinked MF resin. The present investigation revealed that
all of the polymer bound ligands effectively coordinate metal ions like Mn(II),
Fe(III),Co(II),Ni(II),Cu(II) and Zn(II) from their aqueous solution. It was found
that the metal chelation depended much on the pH of the medium. The intake of
metal ions from their solution at their natural pH, follow the order Mn(II),
Fe(III),Co(II),Ni(II),Cu(II) and Zn(II). The optimum pH for the metal intake was
found to be around pH 4.5 for Mn2+, 2.0 for Fe3+, 4.5 for Co2+, 5.0 for Ni2+, 5.5 for
Cu2+,and 3.5 for Zn2+.
It was observed that the extent of sorption decreased as the bulkiness of the
group attached to the azobenzene increased.
In the case of Schiff bases derived from azo derivatives of naphthaldehyde
metal intake was less due to greater steric hindrance. The incorporation of the
ligand functions in a crosslinked macromolecular matrix can impart unique
characteristics to their complexation pattern.
The spectral and magnetic studies of the complexes indicate that
coordination occurs through the azomethine N atom and the phenoxide O. An
octahedral geometry is suggested for the Fe (III), Ni (II) and Cu (II) while the
Co (II) and Zn(II) complexes are tetrahedral.
The ideas obtained from structural elucidation of polymeric Schiff base
metal complexes can be made use of in designing and selecting proper systems for
specific purposes. The selection can be made depending on the reaction conditions
of pH, temperature, product formed etc.
The metal chelates obtained were characterised by analytical and spectral
technique involving IR, UV and ESR spectral techniques. Magnetic susceptibilities
of the complexes were measured by Gouy method. Thermal decomposition studies
of the ligands and their complexes were done on a Dupont 2000 thermobalance.
The kinetic parameters like energy of activation, entropy values were calculated
using Coats-Redfern equation. The negative values of ∆s indicate that the
transition state was more ordered than the reactants. The ideas obtained from
structural elucidation of complexes can be made use of in defining and selecting
proper systems for specific purposes. The selection can be made depending on the
reaction condition.
The Cu(II) complexes are recyclable. The Cu(II) decomplexed resin showed
specificity to Cu(II) in the presence of other metal ions.
*************
REFERENCES
1. Gupta,K.C.Sutar,A.K; LinC C,Coord.Chem.Rev.2009,253,1926
2. Geir G R & sasaki T , Tetrahedron, 55 (1999) 1
3. RLipshutz B H & Shin Y J , Tetrahedron Lett,41(2000) 9515
4. Topich, j inorg. Chem.21 (1982) 2079
5. Akelash,A,Masound,M.S,Kandil.s.S,I.J.Chem25A(1986) 918
6. Padmanabhan M, Kuriakose S & Tessimol.M, I.J.Chem. 34B(1995)903
7. Syamal A &Singh mM, , I.J.Chem. , 37A(1998)350
8. Melby,L.R,J.Am.Chem.Soc. 97(1975)4044
9. Drago,R.S.Goul,Zombeck,S,Staub,D.K,J.Polym.Soc.102(1980) 1033
10. Sherrington,D.C,Hodge,P; Synthesis And Separations using functional Polymers,John
Wiley ,New York (1988)
11. Daly,W.H.Makromol.Chem.Suppl;2 (1979)3
12. Devaky K S George BK ,Pillai VNR Ind.J.Chem.29A ,1045(1990)
13. Regen,S.L.,Besse,J.,J.Am.Chem.Soc.101(1979)4059
14. Regen,S.L.,Besse,J.,J.Am.Chem.Soc.101(1979)4059
15. Dhal P K Arnold H J Macromolecules 25,7051(1992)
16. Buchmeiser,M.R., Kroll,R.,Wrust,K., Macromolecular Symposia 164(2001)187
17. Pillai,V.N.R., Mutter M Top.Curr.Chem.106(1982)119
18. Kumar Dinesh , Kumar Amit Bull.Chem. Soc. Ethiop. 2014, 28(1) 29-36
19. Rivas,B.L.Pooley ,S.A Macromolecular Chemistry and Physics 202 ( 2001) 443
20. Nishide,H., Tsuchida,E., Macromo.Chem., 177(1976) 2295
21. Mathew,B., Pillai, V.N.R, Poly.,Int.28(1992)201
22. Toy.P.H ., Reger.T.S ., J.Comb.Chem .3(2001)117
23. Okay, O., Gurun, C., J.Appl.Polym.Sci 46(1992)401.
24. George , B.K., Pillai, V.N.R., Eur.Polym.J 25(1989)1099
25. Regen, S.L., Besse,J., J.Am.Chem.soc.101(1979)4059
26. Davar, P., Wightman, J.P., Adsorption from aqueous solution, Plenium. NewYork,
N.Y,(1981)163
27. James, R.O.,Healy,T.H., J.Colloid. Interface.Sci. 40(1972)42
28. Kemp, M.V., Weightman,J.P, J.Sc. 32(1981)34
29. Slovak, Z., Docekal,B.,Anal.Chem.Acta. (1980)117,273
30. Slovak, Z., Docekal,B.,Anal.Chem.Acta. (1980)117,273
31. Reinhold, M., Int. Lab. (1982)80
32. Naaktgeboren,A.A., Nolte, R.J.M., Drenth,W., J.Am.Chem.Soc. 102 (1980) 3350
33. Jones,S.R.,Willing,R.I.,Middleton,S.,Ong,A.K.,J.Macromol.Sci.Chem.A10(1976) 875
34. Grubbs, R.H., Gibbons, C., Kroll, L.C., Bonds, W.D., Brubaker, C.H., J.Am. Chem.Soc.
95(1973) 2373
35. Krishnamurthy, M., Hambright, W.P., Morris, K.B., Thorpe, A.N., Alexander,
C.C.,J.Inorg.Nucl.Chem. 31(1973) 873
36. Syamal, A.,Chem. Educn, 4(1987) 33
37. Sherrington, D.C., Hodge, P.,“Synthesis and separations using functional polymers,”
John Wiley, New York (1988)
38. Daly,W.H., Makromol Chem.Suppl.,2(1979)3
39. Kurimura, Y., Adv.Poljm. Sci., 90, (1990) 105
40. Nakamoto, K., Infrared and Raman Spectra of Inorganic and Coordination Compounds,
4th Edn., Wiley, New York, 1986
41. Carlin, R. L. Magnetochemistry, Springer-Verlag, Berlin, 1986
42. Coats, A. W.; Redfern, J. P. Kinetic Parameters from Thermogravimetric Data. Nature
1964, 201, 68-69
43. Kabanov,V.A.,Advances in the Chemistry & Physics of Polymers,283(1973)
ENCLOSURE I
OBJECTIVES OF THE PROJECT
The main objective of the project was to prepare a series of polystyrene supported
Schiff bases and to study their metal intake capacity with Mn(II),
Fe(III),Co(II),Ni(II),Cu(II) and Zn(II) ions and to check the recyclability and
specificity of complexed resins.
Polymer supported metal complexes find wide applications in different fields
of
science and technology. Anchoring of chelating ligands to insoluble
polymer matrix and the
reaction of these chelating resins with metal ions
provide
for
an easy route
the
synthesis
of
immobilised
coordination
compounds .The Schiff bases are an important class of ligands which have
played significant
role in coordination chemistry . Thus there is a further
need to develop highly selective chelating resins with high capacity and
reasonable mechanical strength.
The structural study
of these polymeric metal complexes seems
interesting and useful in view of the numerous applications that such resins
find in organic synthesis, analytical studies , catalytic reactions, biological
systems, etc.
*****************
ENCLOSURE III
SUMMARY OF THE WORK DONE
The present work describes the synthesis and characterisation of
coordination complexes of the polystyrene bound Schiff base with Mn(II),
Fe(III),Co(II),Ni(II),Cu(II) and Zn(II) ions. The chloromethyl polystyrene was
converted to aminomethylated Polystyrene. Azo derivatives of substituted
benzaldehydes and naphthaldehyde were prepared. The aminomethylated
Polystyrene was converted to Schiff bases by refluxing with azo
derivatives.
The molecular character and extent of crosslinking in a polymer support
have a significant effect on the complexation and physicochemical properties of
the metal complexes of polystyrene supported ligands.The present investigation
showed that all of the polymer bound ligands effectively coordinate metal ions like
Mn(II), Fe(III),Co(II),Ni(II),Cu(II) and Zn(II) from their aqueous solution. It was
found that the metal chelation depended much on the pH of the medium. The
intake of metal ions from their solution at their natural pH, follow the order Mn(II),
Fe(III),Co(II),Ni(II),Cu(II) and Zn(II). The optimum pH for the metal intake was
found to be around pH 4.5 for Mn2+, 2.0 for Fe3+, 4.5 for Co2+, 5.0 for Ni2+, 5.5 for
Cu2+,and 3.5 for Zn2+.
It was observed that the extent of sorption decreased as the bulkiness of the
group attached to the azobenzene increased.
In the case of Schiff bases derived from azo derivatives of naphthaldehyde
metal intake was less due to greater steric hindrance. The incorporation of the
ligand functions in a crosslinked macromolecular matrix can impart unique
characteristics to their complexation pattern.
The spectral and magnetic studies of the complexes indicate that
coordination occurs through the azomethine N atom and the phenoxide O. An
octahedral geometry is suggested for the Fe (III), Ni (II) and Cu (II) while the
Co (II) and Zn(II) complexes are tetrahedral.
The ideas obtained from structural elucidation of polymeric Schiff base
metal complexes can be made use of in designing and selecting proper systems for
specific purposes. The selection can be made depending on the reaction conditions
of pH, temperature, and product formed etc.
The metal complexes obtained were characterised by analytical and spectral
technique involving IR, UV and ESR spectral techniques. Magnetic susceptibilities
of the complexes were measured by Gouy method. Thermal decomposition studies
of the ligands and their complexes were done on a Dupont 2000 thermobalance.
The kinetic parameters like energy of activation, entropy values were calculated
using Coats-Redfern equation. The negative values of ∆s indicate that the
transition state was more ordered than the reactants. The ideas obtained from
structural elucidation of complexes can be made use of in defining and selecting
proper systems for specific purposes. The selection can be made depending on the
reaction condition.
The recyclability of the Cu (II) complexes were investigated after decomplexing
with dilute acid. The resin can be recycled several times without reduction in
capacity. The Cu(II) desorbed resins on recycling when treated with Co(II), Ni(II),
Cu(II) and Zn(II) ions selectively took Cu(II) in the presence of other metal ions.
This indicates the selectivity of the conformational prearrangement of the
macromolecules and shows the important role played by fixing a certain location
of functional groups in the chemical reaction of polymers.
************************