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Chapter II
Experimental
Chapter II
Experimental
2.1 Chemicals and Reagents
2.1.1 Solvents
The solvents used in the present investigation are dichloromethane, chloroform,
petroleum ether, methanol, ethanol, diethyl ether, acetone and acetonitrile were
obtained from sd-fine and were purified and dried by conventional methods [1].
2.1.2 Other reagents
¾ Methyl anthranilate, benzaldehyde, p-anisaldehyde, p-nitrobenzaldehyde, nBu4NClO4 from Alfa Aesar.
¾ Diethylether, benzoyl chloride, perchloric acid, hydrazine hydrate from Sd-fine.
¾ Triphenylphosphine, cis-1,2-bis (diphenylphosphino)ethane from Aldrich.
¾ CuCl2.2H2O, Cu(NO3)2.2.5H2O, CuCO3, Cu2O, NaHCO3, Na2SO3, HBF4 from
E-Merck, India
2.2 Synthesis
2.2.1. Metal salts
2.2.1.1 Synthesis of copper(I) chloride
The copper(I) chloride was prepared according to literature procedure [2]. To the
stirred solution of 10 g of copper(II) chloride [CuCl2.2H2O] in 10 ml water, a solution
of 7.6 g anhydrous sodium sulphite (Na2SO3) in 50 ml water was added slowly at
room temperature. The dark brown coloured copper(II) chloride solution was stirred
till the colour disappears and white solid of copper(I) chloride. After complete
addition of sodium sulphite and stirring, CuCl settles readily with greenish
supernatant liquid. The precipitate along with supernatant liquid are then poured in to
about a liter of water containing 1 g of Na2SO3 and 2 ml Conc. HCl. The mixture was
stirred well and allowed to stand until all the CuCl has settled. The precipitate of CuCl
is filtered on suction and quickly washed with dilute sulphurous acid. The CuCl was
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Chapter II
Experimental
washed 4-5 times with 20 to 25 ml of glacial acetic acid, again with absolute alcohol
and six times with 15 ml anhydrous ether. After last washing ether is removed and
white solid transferred to dry watch glass and placed in oven for 20-25 minute.
2.2.1.2. [Cu(MeCN)4]NO3
The Cu(CH3CN)4NO3 was prepared according to literature procedure [3]. To a
solution of Cu(NO3).2.5H2O (0.03 g) in minimum distilled water, equal volume of
acetonitrile and few Cu strips were added. The whole solution was stirred at room
temperature until it turns colourless. The solid product obtained was filtered and dried
under vacuum.
2.2.1.3. Synthesis of [Cu(MeCN)4]ClO4
The copper(I) salt Cu(MeCN)4]ClO4 was prepared according to the literature
procedure [4].
Step I: 1g of CuCO3 was taken in 100 ml beaker and HClO4 was added until
effervescences ceases. It was diluted with distilled water and concentrated up to 1/6 of
the volume. Keeping to overnight, the crystals of Cu(ClO4)2 were formed.
[Precaution- Cu(ClO4)2 is explosive in nature so it should not be too concentrate].
Step II: 20 ml distilled acetonitrile was taken with metallic Cu pieces, 1 spatula of
blue crystals Cu(ClO4)2 was added and the solution was refluxed till the blue colour
disappear. On cooling, white crystals of copper acetonitrile perchlorate comes out.
Metallic Cu reduces Cu(II) to Cu(I). The product was stored in acetonitrile as it is
very hygroscopic in nature.
2.2.1.4. Synthesis of [Cu(MeCN)4]BF4
The [Cu(MeCN)4]BF4 was prepared according to literature procedure with slight
modification [5]. 1.43 g of Cu2O was added to little acetonitrile, the solution was
stirred till the Cu2O dissolved completely. To the dissolved solution, 0.627 g of HBF4
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Chapter II
Experimental
was added and the solution was further stirred for 2 hrs, a white crystals of
[Cu(MeCN)4]BF4 appears. The residue was filtered, washed with absolute alcohol and
with 15 ml anhydrous ether. After washing white solid transferred to dry watch glass
and placed in oven for 20-25 minute. The product was kept in acetonitrile as it is very
hygroscopic in nature.
2.2.2. Synthesis 2-aminobenzoylhydrazide
2-aminobenzoylhydrazide was synthesized by adopting and modifying the reported
method in literature [6, 7] as shown in Scheme 2.1. Hydrazine hydrate (0.625 g, 12.5
mmol) in ethanol was added drop wise to the stirred solution of methyl anthranilate
(1.29 g, 10 mmol) in ethanol and stirred for 1.5 h at 500C. The mixture was then refluxed
for 4 h on water bath. The compound separated on standing over night was filtered
and washed with distilled water. The pure 2-aminobenzoylhydrazide was obtained by
recrystallization from hot ethanol (Yield. 77%, M.P. Thert. 119 °C, Obs. 121 °C).
O
O
OCH3
NH2
NH2NH2 .H2 O
Reflux 4 hrs
N
H
NH2
NH2
Scheme 2.1: Synthesis of 2-aminobenzoylhydrazide
2.2.3. Synthesis of Schiff base ligands:
2.2.3.1. Synthesis of 2(4-substituted-phenyl)-3(4-substituted-benzylamino)-1,2dihydro-quinazolin-4(3H)-one (L1-3)
2-phenyl-3-(benzylamino)1,2-dihydroquinazolin-4-(3H)-one (L1), 2-(4'-methoxyphenyl)-3-(4''-methoxybenzylamino)-1,2-dihydroquinazolin-4-(3H)-one (L2) and 2(4'-nitrophenyl)-3(4''-nitrobenzylamino)-1,2-dihydroquinazolin-4-(3H)-one (L3) were
prepared by adopting and modifying the method described in literature [8,9] as shown
in Scheme 2.2.
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Chapter II
Experimental
To a solution of aromatic aldehydes (2 mmol, 0.212 g, benzaldehyde; 0.272 g, panisaldehyde and 0.302 g, p-nitrobenzaldehyde) was added in an ethanolic solution of
2-aminobenzoylhydrazide (1 mmol, 0.151 g) and the mixture was refluxed for 2h. The
separated solid was collected by filtration, washed with cold ethanol and dried in
vacuo to give the yellow product. This was then characterized by infrared, 1H NMR
and mass spectral studies. (Yield: 86%).
R
O
O
N
H
NH2
NH2
O
H
+
ethanol
2
R
Reflux, 4 hrs
N
N
N
H
R
R = H, OCH 3 , NO 2
Scheme 2.2: Synthesis of 2-(4-substituted-phenyl)-3(4-substituted-benzylamino)-1,2-
dihydro-quinazolin-4(3H)-one
L1: Yield 78%; elemental analysis (C, H, N wt %) Anal. Cal. For C21H15N3O: C, 77.52;
H, 4.65; N, 12.91; Found: C, 77.36; H, 4.48; N, 12.72; IR (KBr) (cm-1): 3276,
υ(NH); 1665, υ(C=O); 1625, υ(C=N); UV-Vis. (CH2Cl2) λmax (nm): 272, 288; 1H NMR
(CDCl3) (400 MHz): 9.19 (s, HC=N), 6.70-7.30 (m, Ar-H), 7.97 (m, N-H).
L2: Yield 81 %; elemental analysis (C, H, N wt %) Anal. Cal. For C23H21N3O3: C, 71.30;
H, 5.46; N, 10.85; Found: C, 71.12; H, 5.32; N, 10.70; IR (KBr) (cm-1): 3280, υ(NH);
1667, υ(C=O); 1622, υ(C=N); UV-Vis (CH2Cl2) λmax (nm): 275, 285; 1H NMR (CDCl3)
(400 MHz): 9.29 (s, HC=N), 6.78-7.42 (m, Ar-H), 7.98 (m, N-H), δ 3.45 (s, OCH3).
L3: Yield 83 %; elemental analysis (C, H, N wt %) Anal. Cal. For C21H15N5O5: C, 60.43;
H, 3.62; N, 16.78; Found: C, 71.12; H, 5.32; N, 10.70; IR (KBr) (cm-1): 3285, υ(NH);
1668 υ(C=O); 1624, υ(C=N); 1565, 1345, υ(NO2); UV-Vis (CH2Cl2) λmax (nm): 278,
285; 1H NMR (CDCl3)(400 MHz): 9.32 (s, HC=N), 6.80-7.45 (m, Ar-H), 7.96 (m, N-H).
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Chapter II
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2.3 Analysis of the complexes
2.3.1 Estimation of Carbon, Hydrogen and Nitrogen
The carbon, hydrogen, nitrogen and sulphur content provide correct picture about
the molecular formula as well as the purity of the compounds. Carbon, hydrogen,
nitrogen and sulphur content of the complexes were estimated on a Thermo Finnegan
FLASH EA-112 CHNS analyzer at IISc, Bangalore.
2.4. Physico-chemical methods:
2.4.1. IR spectroscopy:
The vibrational spectrum of a molecule is considered to be a unique physical
property and is characteristic of the molecule. As such, the infrared spectrum can be
used as a fingerprint for identification by the comparison of the spectrum from an
‘‘unknown’’ with previously recorded reference spectra. The qualitative aspects of
infrared spectroscopy are one of the most powerful attributes of this diverse and
versatile analytical technique. Over the years, much work has been published in terms
of the fundamental absorption frequencies (also known as group frequencies) which
are the key to unlocking the structure spectral relationships of the associated
molecular vibrations. Applying this knowledge at the practical routine level tends to
be a mixture of art and science.
In the most basic terms, the infrared spectrum is formed as a consequence of the
absorption of electromagnetic radiation at frequencies that correlate to the vibration of
specific sets of chemical bonds from within a molecule. First, it is important to reflect
on the distribution of energy possessed by a molecule at any given moment, defined
as the sum of the contributing energy terms (Equation 1):
E total = E electronic + E vibrational + E rotational + E translational
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(1)
Chapter II
Experimental
The translational energy relates to the displacement of molecules in space as a
function of the normal thermal motions of matter. Rotational energy, which gives rise
to its own form of spectroscopy, is observed as the tumbling motion of a molecule,
which is the result of the absorption of energy within the microwave region. The
vibrational energy component is a higher energy term and corresponds to the
absorption of energy by a molecule as the component atoms vibrate about the mean
center of their chemical bonds. The electronic component is linked to the energy
transitions of electrons as they are distributed throughout the molecule, either
localized within specific bonds, or delocalized over structures, such as an aromatic
ring. In order to observe such electronic transitions, it is necessary to apply energy in
the form of visible and ultraviolet radiation (Equation 2):
E = hυ
Frequency/ energy
(2)
The fundamental requirement for infrared activity, leading to absorption of
infrared radiation, is that there must be a net change in dipole moment during the
vibration for the molecule or the functional group under study.
The IR spectroscopy provides information on whether ligand molecules have
coordinated to transition metal cations; if different patterns appear in the free or in the
chelated state, or if characteristic bands exhibit defined shift upon chelation. FTIR
spectroscopy in the framework region (4000-400 cm-1) provides additional
information about the structural details of the support [10, 11]. Infrared spectra of the
ligands as well as their metal complexes were recorded on Perkin Elmer FTIR-100
spectrometer as KBr pellets in the 4000-400 cm-1 spectral range.
2.4.2. UV-visible spectroscopy:
The UV-Vis Spectroscopy is known to be very sensitive and useful technique for
the identification of the electronic state of the metal atom as well as ligand geometry
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Chapter II
Experimental
in complexes. It gives information about the d-orbital splitting through the d-d
transitions and the ligand-metal interaction through the ligand to metal charge-transfer
transitions. The electronic spectra of the ligands and their metal complexes were
recorded on a Shimadzu UV-3600 UV-visible NIR spectrophotometer in the range
200 to 1100 nm. Quartz cell with 10 mm size was used. The radiant energy sources
are the deuterium lamp for the ultraviolet region and a tungsten lamp for the visible
region. A cell containing the pure solvent was used as reference. All the
measurements were made at room temperature.
2.4.3. 1H NMR spectroscopy:
Nuclear magnetic resonance is powerful tool for investing nuclear structure.
Nuclear magnetic resonance is technique that enables us to shape and structure of
molecules. In particular it reveals the different chemical environment of the various
forms of hydrogen present in molecule, from which we are dealing. It is method of
both qualitative and quantitative analysis.
1
H NMR spectra were recorded on a Bruker ACF 300 MHz spectrometer using
[TMS(CH3)4Si] as the internal reference. Chemical shifts were measured on the
δ (ppm) scale and are reported in ppm.
2.4.4. Cyclic voltammetry
Cyclic voltammetry is a technique used to investigate the electrochemical behavior
of the complexes. Cyclic voltammetry consists of cyclic potential of an electrode
immersed in an unstirred solution across two limits, and measuring the resultant
current. The cyclic voltammogram is obtained by measuring the current at the
working electrode during the scan. When the applied potential is sufficiently strong to
reduce the complex a cathodic current is produced and the process occurring as
[Complex]
+
e-
[Complex]49
Chapter II
Experimental
The cathodic current continues to increase until the concentration of complex at
the electrode surface is substantially diminished; causing the current to peak at Ec.
The current then decays as the solution surrounding the electrode is depleted of
[complex] when the electrode becomes a sufficiently strong oxidant, the [complex]which has been accumulating can be oxidized causing an anodic current, peak at Ea.
[Complex]+ +
[Complex]
e-
The forwarded scan produces a new oxidation state; the reverse scan gives
information on the stability of the new complex.
Cyclic voltammetry can be used to investigate the electronic communication
between metal centers in a complex. If two or more metal centers can interact via
intervalence charge transfer (IVCT) then they will have different redox potentials, as
the oxidation of one center will make it more difficult to oxidize another centre; this
may result in different waves in the voltammogram.
Fig. 2.3: Schematic diagram of cyclic voltammetry experiment
Cyclic voltammetry measurements of the ligands and their complexes were
performed with Electrochemical Quartz Crystal Microbalance CHI-400. A three
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Chapter II
Experimental
electrode configuration, consisting of Pt disk working electrode, Pt wire counter
electrode and Ag/AgCl reference electrode containing aqueous 3M KCl were used.
All potentials were converted to SCE scale. All measurements were carried out in
CH2Cl2 solution at room temperature using tetrabutylammonium perchlorate (TBAP)
as supporting electrolyte with scan rate 50 mVs-1.
2.4.5. X-ray diffraction study:
The most powerful tool for the characterization of coordination solids is the single
crystal X-ray crystallography. This technique provides us with an accurate account of
the structure and properties of materials in crystalline state. Additional advanced
analytical and graphical tools associated with this process allows for an in-depth study
of the chemistry of materials and provides us with the means to effectively
communicate these results to others.
In the following paragraphs, we will present a brief introduction to
crystallography and X-ray diffraction as well as some key concepts and terms that are
used throughout this dissertation. The term crystallography, itself, is the study of the
structure and properties of the crystalline state. The notion of what a crystal really is
might be based solely on visual observations, describing crystals as having flat
surfaces with sharp edges such as seen with the precious gems or the all too common
quartz crystals. This definition breaks down when we consider all the crystalline
solids, including polycrystalline solids with crystals so small that the material more
resembles an amorphous powder, than that of a crystalline solid. A more precise
definition is that a crystal consists of atoms that are arranged in a three-dimensional
periodically repeating pattern. These patterns of atoms, as they combine to form
molecules, which in turn form patterns of molecules, are defined by sectioning off the
smallest unit of the solid that repeats over and over again in regular intervals. Each of
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Chapter II
Experimental
these points, called the lattice points, have identical positions within the net with each
point having exactly the same surroundings. Other lattice points in this design can
easily be selected and would be just as valid of choice. Of course, our crystalline
solids reside in a three-dimensional net. We can adjust our design by simply adding
depth to our net, which generates a series of identical parallelepipeds with definite a, b
and c sides and corresponding α, β, and γ angles. Each of these individual
parallelepipeds, are the defining feature of our crystalline solid and are called the unit
cell of the structure. The contents within a unit cell repeat over and over again and, if
we know the atomic arrangement inside a unit cell, we then know the atomic
arrangement of the entire crystalline solid. Smallest repeating collection of atoms
unique for every structure is called the asymmetric unit.
Fig. 2.4 The Unit Cell showing the a, b and c sides as well as the
corresponding α, β, and γ angles.
The asymmetric unit is the most basic form of the crystalline structure as each atom in
this unit are related to all the other atoms in the crystal via a variety of symmetry
elements of which we will explore in greater detail below. Every unit cell is classified
into one of seven crystal systems, each having symmetrical restrictions placed on the
lattice vectors, providing each system with distinctive and unique geometric
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Chapter II
Experimental
parameters. The triclinic system, for example has no restrictions placed on the unit
cell dimensions, while the monoclinic is similar with the exception that α = λ = 90°.
As all possible centering occurrences are taken into account, these seven crystal
systems develop into fourteen Bravais lattices. These types of centering include body
centering (symbol I), C-centered (symbol C), and the centering of all four faces as
face-centered (symbol F). A cell lacking any type of centering is designated as a
primitive (symbol P) cell. The seven crystal systems and the restrictions placed on the
axial systems can be seen in Table 2.1.
Table 2.1 The Seven Crystal Systems
Crystal system
Restriction of the axial system
Triclinic
a ≠ b ≠ c,
α≠β≠λ
Monoclinic
a ≠ b ≠ c,
α = λ = 90°, β > 90°
Orthorhombic
a ≠ b ≠ c,
α = β = λ = 90°
Tetragonal
a = b ≠ c,
α = β = λ = 90°
Trigonal
a = b = c,
α = β = λ ≠ 90°
Hexagonal
a = b,
α = β = 90°, λ = 120°
Cubic
a = b = c,
α = β = λ = 90°
A single crystal of complex suitable for X-ray analysis was obtained by slow
diffusion of diethyl ether into the dichloromethane solution of complex. The intensity
data were collected on a Nonius MACH-3 four-circle diffractometer with graphitemonochromatized MoKα radiation. The structure was solved by direct methods using
the SHELXS 93 program and refined by using SHELXL 97 software [12-14]. The
non-hydrogen atoms were refined with anisotropic thermal parameters. All of the
hydrogen atoms were geometrically fixed and refined using a riding model.
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Chapter II
Experimental
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D.D. Perin, W.L.F. Armarego, D.R. Perin, Purification of Laboratory
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G.J. Cubas, Inorg. Synth. 19 (1979) 90.
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