Download 2008级无机化学研究性实验 Synthesis and Spectral Study of Copper

2008 级无机化学研究性实验
Synthesis and Spectral Study of Copper (II)
Complexes
Zhong Aoshu
College of chemistry and molecular sciences Wuhan University
Abstract. Cu2+ forms different compounds with different ligands. Some of the compounds are
prepared. The spectra and the color of them are measured and observed .Then crystal field theory
and MO are used to explain the results, including the color, Amax and εmax.
Key words. Copper complexes
Spectrochemical series Crystal field theory
1. Introduction
Crystal field theory predicts for transition metal octahedral complexes that the d orbitals are
split into two groups. The original assumption of this theory that the d electrons have a columbic
interaction with the ligands considered as point charges is certainly not correct and a priori
calculation of the crystal field splitting parameter 10 Dq, based on this model are generally in poor
agreement with experimental values. However because of the octahedral symmetry it is true that
the splitting of the d levels predicted by crystal field theory is qualitatively correct. That is,
whatever the nature of the ligand-metal interaction, the dxy, dyz,and dxz orbitals will form a
three-hold equivative (t2g set) and the dx2-y2 and dz2 orbitals will form a two-fold equivalent (eg set)
in the complex. Thus, 10 Dq the energy difference between these two sets, may be determined by
experiment, even though its accurate theoretical calculations are difficult.
Because the values of 10 Dq are is different when different ligands are present, they absorb
different light. Thus they give different colors.
The interpretation of spectra in terms of the spectrochemical series is in principle easily done in
the case of octahedral complexes of metal ion with d9 configurations. In this cases there is no
interaction with d electrons and since the d orbitals interact uniformly with the core of nonvalance
metal electrons the only d lever splitting is due to the interaction of the d orbitals with the ligands,
thus, a single spectral transitions of energies, 10 Dq, is predicted.
2. Experiment
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2008 级无机化学研究性实验
2.1. Materials and instruments
Copper (II) sulfate pentahydrate, hydrochloric acid, glycine, sodium hydrogen carbonate,
ethanol, ice, acetylacetone, ethylenediammine sodium hydroxide, oxalate monohydrate,
chloroform.
Spectrophotometer.
2.2. Preparation of cis-Bis(glycinato) copper(II) Monohydrate (1),(2)
A 3.00 g sample (12.0 mmole) of copper (II) sulfate pentahydrate is dissolved in 17.0 mL of 1.0
M hydrochloric acid. To this solution 1.50g (20.0 mmole) of glycine is added and then warmed in
hot water bath for about 1hour in 50℃. Sodium hydrogen carbonate is added until precipitation is
complete (avoid a large excess). Add about 40 mL of ethanol and cool in ice bath for 30 minutes.
The precipitate is suction filtered, and dried in an oven for 30 minutes in 50℃.After the precipitate
is cooled, weight it .
2.3. Preparation of Bis(acetylacetanato)copper(II) (1)
Etylacetone is prepared by adding 2.50 g (25.0 mmole) of acetylacetone to 100 mL of 0.25 M
NaOH solution (25.0 mmole). This solution is added to a solution of 3.10 g (12.5 mmole) of
copper(II) sulfate pentahydrate in 100.0 mL of water. The precipitates are suction filtered, then add
40.0 mL of ethanol to it and cool in ice bath for 30 minutes and air dried. Weigh it.
2.4. Preparation of potassium bioxalatocuprate(II) (3)
A 6.25g sample (0.025mmole) of copper(II) sulfate pentahydrate is dissolved in 12.5mL of
water. Heat the solution to 90℃ , stir the solution violently and add 18.40 g of oxalate
monohydrate to the solution quickly. Cool the solution to 10℃ in ice bath. The precipitates are
suction filtered, and use 25.0 mL of cool water to wash the precipitate and air dried. Weigh it.
2.5. Spectral study. (4)
Group one: In water solution the complex ion Cu(H2O)62+ is formed. Weigh 0.60 g
Cu(NO3)2·3H2O and 40 g NH3NO3 to prepare 250 mL of 0.01 M Cu(NO3)2 and 2 M NH4NO3
solution. Group two: Add 2.5 mL of 0.1 M NH3·H2O and 22.5 mL of water to 25.0 mL of the
solution prepared, thus we get Cu(NH3)(H2O)52+.Group three: Add 5.0 mL of 0.1 M NH3·H2O to
25 mL of the solution prepared, thus we get Cu(NH3)2(H2O)42+.Group four: Add 7.5 ml of 0.1 M
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2008 级无机化学研究性实验
NH3·H2O and 17.5 mL of water to 25.0 mL of the solution prepared, thus we get
Cu(NH3)3(H2O)32+. Group five: Add 10.0mL of 0.1 M NH3·H2O and 15.0 mL of water to 25 mL of
the solution prepared, thus we get Cu(NH3)4(H2O)22+.Weigh 0.60 g of Cu(NO3)2·3H2O and 25.25g
of KNO3 to prepare 250 ml of 0.01 M Cu(NO)3 and 1 M KNO3 solution. Weigh 0.60g
ethylenediammine to prepare 100 mL of 0.1 M en solution. Group six: Add 2.5 mL of en solution
and 22.5 mL of water to 25 mL of the solution prepared, thus we get Cu(en)(H2O)42+ .Group seven:
Add 2.5 mL of en solution and 22.5 mL of water to 25.0 mL of the solution prepared, thus we get
Cu (en)2(H2O)22+ .Group eight: Weigh 0.12 g of cis-Bis(glycinato)copper(II) monohydrate to
prepare 50 mL of 0.01 M Cu(gly)2(H2O)2 solution. Group nine: Weigh 0.11 g of
Bis(acetylacetanato)copper and chroform to prepare 50 mL of 0.01 M Cu(acac)2 solution. Group
ten: Weigh 0.18 g of potassium bioxalatocuprate ( II ) to prepare 50 mL of 0.01 M
Cu(C2O4)2(H2O)22- solution.
Clean two quartz-cells with distilled water and then put the solution to the tubes, make initial
adjustment to the spectrophotometer before measurement. Except group nine, pure water is the
reference solvent. Chroform is the reference solvent for group nine. Using the spectrophotometer
to measure the absorption with one nm per point and get a list of absorption data. Use Microsoft
office to get the figure below from the date.
0.14
0.25
Absorption/Abs
Absorption/Abs
0.12
0.1
0.08
Group one
0.06
0.04
0.2
Group
Group
Group
Group
0.15
0.1
0.05
0.02
0
0
400
500
600
700
800
900
400
500
λ/nm
Figure 1
600
λ/nm
700
800
Figure 2
0.35
0.4
0.3
0.35
0.25
0.3
0.2
Absorption/Abs
Absorption/Abs
two
three
four
five
Group six
Group seven
0.15
0.1
0.05
2.5
2
0.25
1.5
0.2
1
0.15
0.1
0.5
0.05
0
400
500
600
λ/nm
700
0
400
800
Figure 3
0
500
600
λ/nm
Figure 4
3
700
800
Group ten
Group eight
Group nine
2008 级无机化学研究性实验
3. Results and discussion.
Table 1. Color, λmax, Amax and concentration for complexes studied
Group
Complex
Color
number
λmax
λmax (literature) nm
Amax Abs
nm
C
mol/L
One
Cu(H2O)62+
no
811
794
0.13204
0.001
Two
Cu(NH3)(H2O)52+
Light blue
766
745
0.0869
0.005
There
Cu(NH3)2(H2O)42+
Blue
719
680
0.1922
0.008
Four
Cu(NH3)3(H2O)32+
Blue
660
645
0.1024
0.005
Five
Cu(NH3)4(H2O)22+
Dark blue
639
591
0.1157
0.005
Six
Cu(en)(H2O)42+
Light blue
660
658
0.1520
0.005
Seven
Cu(en)2(H2O)22+
Purple
547
549
0.2939
0.005
Eight
Cu(gly)2(H2O)2
Dark blue
628
630
0.3623
0.01
Nine
Cu(acac)2
Dark green
656
650
0.3672
0.01
Ten
Cu(C2O4)2(H2O)22-
Light blue
713
---
0.3266
0.01
Half of the absorption max is a little different from the literature data, the spectrometer itself
may have some deviations. But the date is not very good when water and ammonia serve as
ligands. We assume that the concentration of aqueous ammonia may not be true because ammonia
is highly volatilizable. What’s more, there may exist other species in the solution, so we can not
get very exalt date.
Table 2. Yields of the complexes prepared.
Complex
Mass g
Yield
Yield(literature)
Cu(gly)2·H2O
2.15
92.7%
>90%
Cu(acac)2
2.53
76.7%
---
K2[Cu(C2O4)2]·2H2O
8.07
91.2%
97%
The yields are very good because the experiment is done carefully.
In Cu2+ and ammonia solution,NH4NO3 acts as a buffer, so there are not participants in the
solution.
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2008 级无机化学研究性实验
4. Conclusion
Because the absorption max for Cu(H2O)62+ does not lie in the visual area, it does not have color.
Cu(en)2(H2O)22+ appears purple in aqueous solution. Hydrated Cu2+ is a d9 ion. Because the
absorption max for it is 547 nm, the energy difference between t2g and eg orbitals in this is
correspond to the energy of photos spanning the green and yellow range, when white light shine
on the solution, these colors of light are absorbed, transmitted, so the solution appears purple. The
color of others can be explained in the similar way as that of Cu(en)2(H2O)22+.
When more NH3 are added to Cu2+, λmax becomes smaller. That is to say, light of higher energy is
absorbed and the energy difference between t2g and eg orbitals is greater. That indicates that NH3 is
a stronger ligand than water. The λmax of Cu2+ and ammonia solution is bigger than that of Cu2+
and en solution. What’s more, en is a chelate, they both use N atom as donor atom, so en is a
stronger ligand then NH3. The λmax of Cu(gly)2(H2O)2 is bigger than Cu(acac)2, so gly is a stronger
ligand than acac. The λmax of Cu(ox)2(H2O)22- is smaller than that of Cu(H2O)62+ and bigger than
that of Cu(acac)2, so ox2- is a stronger ligand than water and weaker ligand than acac.We get the
spectrochemical series.
H20<ox2-<acac< (gly NH3) <en
As the date is not very well, the strength of gly and NH3 can not be compared.
For group nine, it appears to have only one absorption max. The reason that the second crystal
field transition is not readily detected is that it is obscured by the intense absorption of light
associated with electronic transitions between orbitals that are primarily ligand-like in nature.
Such transition are called charge transfer transitions and commonly are associated with much
stronger absorption of light than are crystal filed transitions.
εmax
indicates how intense the absorption is.
εmax for group one to five
are relatively small compared to those from group six to ten. This
qualitatively explained by the lower symmetry of the chelate complexes. Specifically the chelates
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2008 级无机化学研究性实验
lack a center of symmetry whereas the complexes from group one to five have a center of
symmetry. Since the absorption of light should be completely forbidden. By the electron dipole
mechanism, we may anticipate that a centrosymmetric would show weaker transitions even though
vibrations always cause small instantaneous from the centrosymmetric arrangements.
Using MO, Orgel diagram can be used to explain the phenomenon. Only one kind of transfer is
possible according to the diagram. (5)The transitions are all d-d transition .They are all
spin-allowed and Larport-forbidden, so the absorptions are all not strong.
Figure five
5. Acknowledgement.
We thank all the teachers in Wuhan University that helped us during the experiment. They give us
help and sound instructions when we need.
6. Literature cited.
(1)Potts Richard. Synthesis and spectral Study of Copper (II) Complexes. Journal of chemical
education, 51 (1974): 539.
(2)Du Xiangge. Preparation and Characterization of the chelate of glycine with Copper.
Journal of Anhui Agri .Sci .2009, 37(5):1897 – 1898.
(3)Muttertiles Earl. Inorganic synthesis (Vol ten). McGraw-Hill Book Company, Inc.New
York, London, 1967.
(4)Trapp chrles, Johnson Richard. Crystal field spectra of transition metal ions. Journal of
chemical education, 44 (1967): 527-530.
(5)Housecroft Catherine, Sharpe Alan. Inorganic chemisty.Second edition. Prentice Hall,
2005.
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