A study of estimation of excited state dipole moments of di(4-bromophenyl)carbazone and its Cu(II), Zn(II), Cd(II) complexes from the solvent effect on their electronic spectra

Article abstract of DOI:10.1016/j.saa.2003.11.029

The solvent effect on the electronic spectra of di(4-bromophenyl)carbazone and its Cu(II), Zn(II), Cd(II) complexes have been studied by synthesizing and characterizing them by magnetic moment, IR, EPR and ¹H NMR spectral measurements. The electric dipole moments of these compounds in the first electronically excited state have been determined. The results indicate that the observed band systems in these compounds may be attributed to π* ← π transition.

Full text of DOI:10.1016/j.saa.2003.11.029

Spectrochimica Acta Part A 60 (2004) 2499–2503
A study of estimation of excited state dipole moments of
di(4-bromophenyl)carbazone and its Cu(II), Zn(II), Cd(II) complexes
from the solvent effect on their electronic spectra
A.H.M. Siddalingaiaha,∗, Sunil G. Naika, H.D. Patilb
a
Department of Chemistry, Karnatak University, Dharwad 580003, India
b
Department of Physics, Basaveshwara Science College, Bagalkote 587101, India
Received 11 April 2001; received in revised form 2 September 2003; accepted 17 November 2003
Abstract
The solvent effect on the electronic spectra of di(4-bromophenyl)carbazone and its Cu(II), Zn(II), Cd(II) complexes have been studied by
synthesizing and characterizing them by magnetic moment, IR, EPR and 1H NMR spectral measurements. The electric dipole moments of
these compounds in the first electronically excited state have been determined. The results indicate that the observed band systems in these
∗
compounds may be attributed to ␲ ← ␲ transition.
© 2004 Published by Elsevier B.V.
Keywords: Solvent effects; Dielectric constants and dipole moment
1. Introduction
states, it is also possible from these studies to determine
the shape parameters, which is another important parameter
that gives knowledge about the shape of the cavity in which
solute molecule is supposed to lie.
Literature survey reveals that diphenylcarbazone (DPC)
is widely used as a spectrophotometric reagent for the de-
termination of chromium in ore [1], sea water [2], animal
tissue digests [3] etc.; there seems to be no reports on its
electronic spectral studies and dielectric measurements. No
studies have been reported on di(4-bromophenyl)carbazone,
nor on its Cu(II), Zn(II) and Cd(II) complexes. Dipole mo-
ment is an important parameter [4,5] which gives an idea
of the electronic structure of the molecule and is of prime
importance in understanding the molecular interactions. The
present studies have been undertaken keeping these views in
mind. From the study of the solvent effect on the electronic
spectrum of the above compounds, it is possible to determine
its electric dipole moment in its electronically excited states.
This parameter so determined gives, some insight into elec-
tron distribution, reactivity, photochemical reactions etc., of
the solute molecule in its electronically excited states. Apart
from obtaining the permanent dipole moment in the excited
2. Experimental
2.1. Apparatus
Electronic spectra were recorded on Hitachi 150-20
UV-Vis spectrophotometer. Elemental analysis was carried
1
out on Perkin-Elmer 240 CHN analyser. IR and H NMR
spectra were recorded on Nicolet-170 FT IR spectrometer
and VXR 300 S Varian spectrometer, respectively. EPR
spectra of Cu(II) complex was recorded on a EPR-E-4 spec-
trometer, operating in the X-band region with TCNE as the
reference material at liquid nitrogen temperature. The mag-
netic moment of Cu(II) complex was found out by Gouy
method. The metal estimation was done by EDTA titration
method [6]. The dielectric measurements were recorded
with the help of Forbes Tinsley (FT) 6421 LCR data bridge
at 10 kHz frequency. The refractive indices of various dilute
solutions for sodium D line were determined, using Abbe’s
refractometer.
∗
Corresponding author. Tel.: +91-836-74784; fax: +91-836-776943.
E-mail addresses: chemisunil@rediffmail.com,
ahmschemi@rediffmail.com (A.H.M. Siddalingaiah).
1386-1425/$ – see front matter © 2004 Published by Elsevier B.V.
doi:10.1016/j.saa.2003.11.029

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A.H.M. Siddalingaiah et al. / Spectrochimica Acta Part A 60 (2004) 2499–2503
2.2. Reagents
ders kept in position with small strips (to achieve electric
isolation) and their leads are coated with gold. This assem-
bly is kept in a glass beaker so that dilute solution can be
filled into the cell. The capacitance of the empty cell (air)
would be of the order of pico- Faraday.
Carbontetrachloride, isopropyl alcohol, dimethylfor-
mamide, butanol-1, chloroform, 1,4-dioxane, n-propyl al-
cohol used were of Fisher AR grade. Benzene (Fluka) used
was of spectroscopic grade. Copper chloride, zinc chloride
and cadmium chloride used were of Fisher AR grade.
3. Results and discussion
2.3. Preparation of the ligand
3.1. Characterization of ligand and the complexes
It was synthesized by a method described earlier [7,8].
Di(4-bromophenyl)carbazide was prepared by heating a
mixture of 4-bromophenylhydrazine and urea (2:1) at
155–160 ◦C for about 3 h. The crude carbazide so obtained
was crystallized from ethyl alcohol. About 1 g of the car-
bazide was dissolved in a mixture of 60 ml glacial acetic
acid, 20 ml of 1N sulfuric acid and 2–3 drops of 10% ferric
alum and oxidized by adding 20 ml of 0.06 M potassium
persulfate (K2S2O8) dropwise with vigorous stirring for
about 30 min. The resulting carbazone (D4BrPC) was ex-
tracted with ether, washed several times with water, dried
and purified by column chromatography using silica gel
(60–120 mesh) column. A mixture of Me2CO:CHCI3 (1:4)
is used as an eluent.
The elemental analyses of the ligand and the complexes
along with the magnetic data are reported in Table 1. The
C, H, N and metal analyses confirm that the stoichiometry
of the complex is 1:2 for metal to ligand. The magnetic
moment for the copper complex is 1.58 BM, which can
be interpreted in terms of weak Cu–Cu interaction [10].
The Cu–Cu interaction is also confirmed by EPR spectrum
analysis.
3.2. IR spectra
The IR spectra of the ligand and the complexes were
recorded in 4000–400 cm−1 range. The ligand showed
bands at 3312, 3090 which may be attributed to –NH vi-
Yield 60%, mp, 108 ◦C.
brations. The band at 1712 cm−1 is assigned to (>C O)
=
=
stretching. The disappearance of (>C O) stretching band
2.4. Preparation of the complexes
around 1700 cm−1 in the spectra of the complexes indi-
cated that oxygen atom of the ligand is involved in the
coordination with the metal through the enolic form. This
was further confirmed by the appearance of a band around
About 1 g of copper chloride was dissolved in an ac-
etate buffer (pH 4.5) and added to an alcoholic solution of
D4BrPC dropwise at room temperature. The mixture was
stirred for about 30 min and the resulting precipitate was col-
lected under suction and washed several times with water.
The complex was dried over P2O5 under vacuum at room
temperature and purified by Soxhlet method [9].
1600 cm−1 due to –C N stretching in the spectra of the
=
complexes. The IR peaks of the ligand and the complexes
are given in the Table 2.
3.3. 1H NMR spectra
The zinc and cadmium complexes were similarly prepared
by using the acetate buffer of pH 6.2.
The 1H NMR spectrum of the ligand was recorded using
CDCl3 as solvent and the TMS as an internal reference. The
broad signals at δ 5.9 and 6.40 are due to aniline –NH and
amide –NH groups, respectively. The multiplets observed in
the region δ 6.5–7.8 may be attributed to aromatic hydrogen
atoms. It is observed for the diamagnetic Zn(II) and Cd(II)
complexes that the broad signal of amide –NH has disap-
peared indicating that the azo nitrogen atom is involved in
the coordination to the central metal atom through deproto-
nation. The data is given in Table 2.
2.5. Measurements of dielectric constant
The dielectric constants of the dilute solutions were mea-
sured in a suitably fabricated cell of usually of small capac-
itance where the accurate determination of small changes in
capacitance would be possible. This small capacitance can
be measured with the help of Forbes Tinsley (FT) 6421 LCR
Data Bridge at 10 kHz frequency. The necessary dielectric
sample holder should consist of two concentric brass cylin-
Table 1
Analytical, magnetic moment data of the compounds
Compound
Found/(calculated) (%)
C
Molecular formula
µeff (BM)
H
N
M
–
D4BrPC
39.17 (39.22)
36.61 (36.41)
36.43 (36.33)
34.71 (34.45)
2.59 (2.54)
2.05 (2.12)
2.19 (2.12)
2.11 (2.01)
14.13 (14.08)
13.18 (13.07)
13.21 (13.04)
12.43 (12.36)
C
13H10N4OBr2
C26H18N8O2Br4Cu
26H18N8O2Br4Zn
C26H18N8O2Br4Cd
–
1.58
–
Cu(D4BrPC)2
Zn(D4BrPC)2
Cd(D4BrPC)2
7.31 (7.40)
7.73 (7.61)
12.51 (12.40)
C
–

A.H.M. Siddalingaiah et al. / Spectrochimica Acta Part A 60 (2004) 2499–2503
2501
Table 2
IR frequencies and 1H NMR data of the compounds
Compound
IR frequencies (cm−1
)
1H NMR
ν(–NH)
ν(C
ν(C
νCar
ν(C–O)
ν(N–H) Bend
=
=
N)
O)
=
O
D4BrPC
3312, 3090
1712
–
1486
–
771
5.9 br (–NH phenyl) 6.4 br (–NH amide)
6.5–7.8 m (–H aromatic)
–
5.83 br (–NH phenyl) 6.7–8.1 m (–H aromatic)
5.75 br (–NH phenyl) 6.3–7.8 m (–H aromatic)
Cu(4BrPC)2
Zn(D4BrPC)2
Cd(D4BrPC)2
3123
3171
3132
–
–
–
1603
1612
1597
1463
1453
1471
1131, 1250
1150, 1212
1171, 1241
758
763
769
ar = Aromatic.
3.4. EPR spectra
In the EPR spectra, from the observed of value of
are recorded on a Hitachi 150–20 UV-Vis spectrophotome-
ter with a cell path length of 1 cm, in various polar and
non-polar solvents (concentration 0.01–0.03 gm l−1). The
data is represented in Tables 3 and 4. The permanent dipole
moments in the excited states (µe) and the radius of the
cavity in which the solute molecule supposed to lie are
obtained by using the method reported in the literature as
follows:
Following Suppan and Tsiamis [11], the change in the
permanent dipole moment for a series of solvents of different
static dielectric constants (ε) but similar refractive indices
(n) is related to the observed energy shift ꢀνa–b between
solvents a and b by
Cu(II) complex at liquid nitrogen temperature (g = 2.20,
ꢀ
g = 2.07), it is evident that the unpaired electron is pre-
⊥
dominantly in dx2 − y2 orbital with the possibility of
some dz2 with it because of low symmetry. The g value
ꢀ
(g = 2.20 < 2.3) indicates a larger percentage of cova-
ꢀ
lency. The G value, which is, less than four confirms a weak
interaction between copper centres. The relation g /A =
ꢀ
ꢀ
119 cm−1 suggests the square planar geometry. Based on
the analytical and spectral data, the structure of the ligand
and the complexes are assigned as shown in Fig. 1(a and
b), respectively.
µg · ꢀµg−e
−ꢀνa−b
=
{ꢀ[f(ε) − f(n2)]a−b
}
hca3g
3.5. Evaluation of ground state and excited
state dipole moment
µ2e − µ2g
+
ꢀf(n2)a−b
(1)
hca3g
The UV absorption spectra (for S1 band) of a single par-
ticular weight fraction (concentration) of each of the pure
samples D4BrPC and its Cu(II), Zn(II), Cd(II) complexes
where µg is the permanent dipole moment in the ground
state, h the Planck’s constant, c the velocity of light and, ag
the radius of the of the cavity in which the solute molecule is
supposed to lie and f(ε), f(n2) are the polarity polarizability
functions defined by
N=N-C-NH-NH
O
Br
Br
2(ε − 1)
(2ε + 1)
2(n2 − 1)
(2n2 − 1)
f(n2) =
, respectively.
(a)
f(ε) =
,
Br
Recently a method is proposed by Ayachit et al. [12] to
determine µe by expressing Eq. (1) in the form
HN
N
Br
X
Y
+
= 1
(2)
C1
C2
N
O
O
N
C
C
N
which is an equation of a straight line with intercepts on ei-
ther axes. By plotting the graph between X( = ꢀ[f(ε) −
f(n2)]a−b/−ꢀνa−b) and Y(= ꢀf(n2)a−b/−ꢀνa−b) the in-
tercepts C1[= hca3g/µg ·ꢀµg−e] and C2[= hca3g/(µe2 −µ2g)]
on the X and Y axes, respectively, are determined and the
magnitude and direction of them are obtained. The required
data are obtained by measuring static permitivities of sol-
vents and various dilute solutions (in benzene only for this
purpose) at 10 kHz with the help of Forbes Tinsley (FT)
6421 LCR data bridge. The estimated values of µg using
Guggenheim’s modified equation [13] are estimated to be
M
N
N
Br
NH
Br
(b)
Fig. 1. (a) Structure of the ligand; (b) suggested structure of the complexes
(M = Cu(II), Zn(II) or Cd(II)).

2502
A.H.M. Siddalingaiah et al. / Spectrochimica Acta Part A 60 (2004) 2499–2503
Table 3
Dielectric constants and refractive indices of the compounds in benzene at 25 1 ◦C d1 = 0.874, ε1 = 2.278, n1 = 1.5010
Compound
Molecular
weight (M2) fraction (W2)
Weight
Dielectric
constant (ε12
ε12 − ε1/ Refractive
n212 − n21/
Intercepts
Calculated
µg (D)
)
W2
index (n12
)
W2
ꢁ
ꢁꢁ
∆
∆
∆
Eq. (3) Eq. (4)
D4BrPC
398.08
0.5112 × 10−3 2.3812
201.88
154.23
128.79
110.84
97.32
1.5043
1.5060
1.5065
1.5073
1.5080
19.4024
13.3891
10.2296
8.9698
212.50 19.50 193.30 26.54
27.41
39.22
42.83
37.31
1.1230 × 10−3 2.4512
1.6171 × 10−3 2.4932
2.1130 × 10−3 2.5122
2.7621 × 10−3 2.5468
0.5231 × 10−3 2.3711
1.1133 × 10−3 2.4351
1.4967 × 10−3 2.4756
2.2231 × 10−3 2.4973
2.5312 × 10−3 2.5021
0.6121 × 10−3 2.4112
1.0231 × 10−3 2.4421
1.5102 × 10−3 2.4763
2.0131 × 10−3 2.4982
2.6131 × 10−3 2.5131
0.7215 × 10−3 2.3912
1.1532 × 10−3 2.4131
1.6053 × 10−3 2.4532
2.1562 × 10−3 2.4912
2.5138 × 10−3 2.5039
7.6261
Cu(D4BrPC)2 857.57
Zn(D4BrPC)2 859.51
Cd(D4BrPC)2 906.53
177.98
141.11
132.00
98.65
1.5048
1.5063
1.5067
1.5075
1.5080
21.8372
14.3175
11.4551
8.7968
201.92 22.42 179.5
37.54
88.54
8.3217
217.60
160.39
131.31
109.38
89.97
1.5040
1.5050
1.5057
1.5063
1.5075
14.7296
11.7535
9.3580
7.9180
7.4839
240.22 16.11 224.11 42.00
172.92 19.00 153.92 35.75
156.90
117.15
109.14
98.88
1.5053
1.5060
1.5070
1.5075
1.5080
17.9184
13.0385
11.2434
9.0698
89.86
8.3793
Table 4
The electronic spectral data of the compounds in different solvents
Solvents
D4BrPC
Cu(D4BrPC)2
Zn(D4BrPC)2
Cu(D4BrPC)2
νmax (cm−1
)
ꢀν (cm−1
)
νmax (cm−1
)
ꢀν (cm−1
)
νmax (cm−1
)
ꢀν (cm−1
)
νmax (cm−1
)
ꢀν (cm−1
)
Cyclohexane
Carbon tetrachloride
Benzene
Isopropyl alcohol
Dimethylformamide
Butanol-1
Chloroform
1,4-Dioxane
n-Propyl alcohol
44198
33821
42570
46321
34574
42718
40892
32112
47410
Reference
10377
1628
2123
9624
1480
3306
12086
3212
44512
34410
36121
35496
35621
43113
40821
31689
47197
Reference
10102
8391
9016
8891
1399
3691
12823
2685
44821
34232
34681
36123
35628
40891
40813
32125
47138
Reference
10589
10140
8698
9193
3930
4008
12696
2317
44971
34380
34921
35820
37213
39923
40623
32231
47328
Reference
10591
10050
9151
7758
5048
4348
12740
2357
Table 5
Values of X, Y intercepts and molecular radius (ag) of the compounds
Solvents
D4BrPC
Cu(D4BrPC)2
Zn(D4BrPC)2
Cd(D4BrPC)2
X × 10−5
Y × 10−4 X × 10−5
Y × 10−5 X × 10−5
Y × 10−5 X × 10−5
Y × 10−5
Carbon tetrachloride
Benzene
0.2356
0.4377
0.0210
0.2900
0.2420
0.0849
0.2154
0.5627
0.2309
0.0703
0.2055
0.4657
0.2308
0.7091
0.2055
0.4699
Isopropyl alcohol
Dimethylformamide
Butanol-1
26.1976
6.1325
36.0217
9.0346
−0.1599
6.1688
6.6381
38.1063
8.0922
−0.3764
6.3943
6.4200
13.5651
7.4522
−0.3902
6.0778
7.6075
10.5608
6.8694
−0.3709
0.0031
0.0336
0.0325
0.0385
−0.1265
0.0397
−1.3385
0.3556
−0.4765
0.3275
−0.3710
0.3019
Chloroform
1–4 Dioxane
n-Propyl alcohol
Intercepts C1
C2
Molecular radius
(ag) (Å)
0.3596
17.2615
11.4300 × 10−5
0.0872 × 10−4
3.9577
−0.0021
0.3390
−0.0209
0.3423
−0.0211
0.3412
−0.0210
−0.0907
20.6495
5.6600 × 10−5
0.2537 × 10−5
5.0405
−1.0854
23.9292
4.8837 × 10−5
0.3006 × 10−5
5.0513
−1.2577
23.5231
5.0000 × 10−5
0.3072 × 10−5
5.0633
−1.2364

A.H.M. Siddalingaiah et al. / Spectrochimica Acta Part A 60 (2004) 2499–2503
2503
Table 6
the literature for some polymers both in polar and non-polar
solvents. The method of calculation (vector addition of group
moments) has its own limitation of not accounting for the
possible inductive/mesomeric/hydrogen bonding effects in
these systems. Under the circumstances if it is assumed that
these values would not improve much when bonding effects
are also taken into account, the presently observed dipole
moment values remain higher. In the light of these consid-
erations the observed values of the dipole moments may be
considered as inductive of the fact that the present ligand
and complexes are associated rather with large values of
dipole moments which in turn may be taken as suggestive
of having their structure [14].
Ground state and excited state dipole moments
Compound
D4BrPC
Eq. no.
µg (D)
µe (D)
θ (◦)
From (3)
From (4)
26.54
27.41
46.01
46.52
60.75
59.69
Cu(D4BrPC)2
Zn(D4BrPC)2
Cd(D4BrPC)2
From (3)
From (4)
37.54
39.22
106.97
107.57
76.24
75.03
From (3)
From (4)
42.00
42.83
101.42
101.77
73.08
72.51
From (3)
From (4)
35.75
37.31
98.37
98.95
77.96
76.27
The dipole moment values of the excited states are ex-
pected to be greater than their ground state values. In the
present investigation, the excited state dipole moment val-
ues are certainly greater than the ground state values. Based
on these observations, it may be presumed that the observed
accurate up to second decimal place. The equations used are
as follows:
ꢀ
ꢁ
1/2
3
M2
µg = 0.0128
×
(3)
(ε1 + 2)2
d1 × T × ∆
∗
transitions belong to ␲ ← ␲.
where ∆ = ∆ꢁ − ∆ꢁꢁ = [(ε12 − ε1)/W2]w →0 − [(n2
−
2
12
n2)/W2]w →0 also
2
1
References
µg = 0.0128
ꢂ
ꢃ
1/2
ꢀ
ꢁ
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[2] S. Tsunenbu, G. Shiro, Bull. Inst. Chem. Res. Kyto Univ. 55 (1977)
429.
[3] W.C. Bryson, C.M. Goodall, Anal. Chim. Acta 124 (1981) 391.
[4] C.P. Smyth, Dielectric Constant and Molecular Structure, New York,
1931.
[5] M.L.E. Sutton, Bull. Soc. Chim., France, 1949, p. D81.
[6] H.A. Flaschka, EDTA Tritrations, Pergamon Press, London, 1959,
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[7] A.H.M. Siddalingaih, S.G. Naik, J. Mol. Struct. (Theochem) 581
(2002) 149.
3
M2
(ε12−ε1)
×
×
(ε1+2)2 d1 × T × 0.97
W2
w2→0
(4)
The quantities n, d, M, W and T involved in Eqs. (3)
and (4) are the refractive index, density, molecular weight,
weight fraction and absolute temperature, respectively. The
suffix 1, 2 and 12 refers to the solvent, solute and solution,
respectively. The data of dielectric constants, the refractive
indices and hence the ground state dipole moment for the
compounds are presented in Table 3. The values of X, Y
intercepts are presented in Table 5.
[8] A.H.M. Siddalingaiah, A.F. Dodamani, S.G. Naik, Spectrochim. Acta
57A (2001) 2721.
[9] A.I. Vogel, Text Book of Practical Organic Chemistry, 3rd ed.,
London Press, London, 1964, p. 153.
The magnitude and orientations of the dipole moment
for the first excited state together with the corresponding
ground state dipole moment values are given in Table 6. It
may be observed that the excited dipole moment values are
fairly higher when compared to the values obtained by using
Guggenheim equation for ground state ones (as entered in
column three of Table 6). Such large values are reported in
[10] B.J. Hathway, D.E. Billing, Coord. Rev. 5 (1970) 143.
[11] P. Suppan, C. Tsiamis, Spectrochim. Acta 36A (1983) 971.
[12] N.H. Ayachit, D.K. Deshapande, M.A. Shashidhar, K. Suryanarayana
Rao, Spectrochim. Acta 42A (1986) 585.
[13] E.A. Guggenheim, Trans. Farad. Soc. 45 (1949) 714; 47 (1951) 573.
[14] N.E. Hill, W.E.Voughan, A.H. Price, M. Davies, Dielectric Properties
and Molecular Behaviour, the Van Nostrands Series in Physical
Chemistry, Van Nostrand Reinhard, London, 1969.