Synthesis and spectral feature of benzophenone-substituted thiosemicarbazones and their Ni(II) and Cu(II) complexes

Article abstract of DOI:10.1016/j.saa.2008.07.005

The ligational behavior of 2-hydroxybenzophenone and 2-hydroxy-4-methoxybenzophenone N-substituted thiosemicarbazones towards Ni(II) and Cu(II) ions has been investigated. The isolated complexes were identified by elemental analyses, molar conductance, ma

Full text of DOI:10.1016/j.saa.2008.07.005

Spectrochimica Acta Part A 71 (2009) 1885–1890
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis and spectral feature of benzophenone-substituted
thiosemicarbazones and their Ni(II) and Cu(II) complexes
A.A. El-Asmya,∗, G.A.A. Al-Hazmib
a Chemistry Department, Faculty of Science, Mansoura University, Mansoura, Egypt
b Chemistry Department, Faculty of Science, Taiz University, Taiz, Yemen
a r t i c l e i n f o
a b s t r a c t
Article history:
The ligational behavior of 2-hydroxybenzophenone and 2-hydroxy-4-methoxybenzophenone N-
substituted thiosemicarbazones towards Ni(II) and Cu(II) ions has been investigated. The isolated
complexes were identified by elemental analyses, molar conductance, magnetic moment, IR, UV–vis and
ESR spectral studies. The IR spectra indicated that the investigated thiosemicarbazones lost the N2 proton
or the N2 and OH protons and act as mononegative or binegative tridentate ligands. The ligands contain-
ing methoxy group facilitate the deprotonation of OH by resonance more than the SH. Most of the Ni(II)
complexes measured subnormal magnetic moments due to square-planar + tetrahedral configuration and
supported by the electronic spectra. The percentage of square-planar to tetrahedral was calculated and
found in agreement with the ligand splitting energy (10Dq). Also, Cu(II) complexes measured subnormal
values due to the interaction between copper centers; the lower the value the higher the interaction. It
was found that the substitutent has a noticeable effect on the distortion of the complex. The ESR spectra
Received 7 June 2008
Received in revised form 3 July 2008
Accepted 5 July 2008
Keywords:
Complexes
Thiosemicarbazone
ESR spectra
Magnetic moments
of some solid Cu(II) complexes at room temperature exhibit g > g > 2.0023 confirming a square-planar
||
⊥
structure.
© 2008 Elsevier B.V. All rights reserved.
1. Introduction
groups favored oxidation to Cu(III) [7]. Co(II), Ni(II) and Pt(IV)
complexes of these thiosemicarbazones were studied [8–10]. Also,
there has been an interest in thiosemicarbazones derived from
salicylaldehyde, 2-hydroxyacetophenone, 2-aminobenzaldehyde,
and 2-aminoacetophenone with substitution at the N(4) position
[11–14]. It was also reported many complexes having different
geometries [15–17].
Sulfur compounds and their metal complexes have antimicro-
bial activity and showed a high dependence on their substitutents
[1]. The activity may be due to the presence of multicoordination
centers having the ability to form stable chelates with the essential
metal ions in which the organisms need in their metabolism [2].
Transition metal complexes for several of these compounds have
also been screened for medicinal properties [3]. Diacetylmonoxime
thiosemicarbazone was found effective against vaccinia infections
in mice which probably acting by removing some essential metal
ions from vaccinia virus by chelation [4]. Mononuclear and polynu-
clear Cu(II) complexes of thiosemicarbazones serve as models for
galactose oxidase and used as an effective oxidant and redox cat-
alysts [5,6]. The redox properties of mononuclear and binuclear
copper(II) chelates were investigated. The effect of substitutents
on E1/2, redox properties and stability towards oxidation of the
complexes was related to the electron-withdrawing or releasing
ability of the substitutents on the C N1 [H, CH3 or C6H5] and/or
N4H [H, C2H5, C6H5 or pClC6H5] groups. The electron attracting sub-
stitutents stabilized the Cu(II) complexes while electron-donating
In the work reported herein, compounds having N4- and N3-
substituted thiosemicarbazones (Fig. 1) and their Ni(II) and Cu(II)
complexes have been studied focusing on the spectra and magnetic
properties.
2. Experimental
2.1. Synthesis of ligands
The investigated thiosemicarbazones (see Table 1 for full
and abbreviated names) were prepared similar to those
reported earlier [10] by condensation of 1:1 molar ratio of 2-
hydroxybenzophenone or 2-hydroxy-4-methoxy-benzophenone
with 4-methyl-, 4-phenyl- or 3-pipridylthiosemicarbazides (pre-
pared in our laboratory except 4-methylthiosemicarbazide which
purchased from Fluka) in ethanol. The reaction mixture was heated
under reflux on a water bath for 2–3 h in the presence of five drops
of glacial acetic acid. The formed precipitate was separated by
∗
Corresponding author. Tel.: +20 101 645966.
E-mail address: aelasmy@yahoo.com (A.A. El-Asmy).
1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2008.07.005

1886
A.A. El-Asmy, G.A.A. Al-Hazmi / Spectrochimica Acta Part A 71 (2009) 1885–1890
2.2. Synthesis of complexes
The complexes were prepared by heating under reflux 1:1 molar
mixture of each ligand (3 mmol) and metal acetate (3 mmol) in
ethanol medium (50 ml) on a water bath for 4–6 h. The precipitate
was filtered off, washed with ethanol and diethylether and finally
dried in a vacuum desiccator.
2.3. Measurements
Partial elemental analyses (C, H and N) were performed at the
Microanalytical Unit of Cairo University. Nickel and copper analyses
were carried out [18] just to confirm the formation of complexes
(the data are not included). The IR, as KBr discs, on a Mattson 5000
FTIR Spectrophotometer (400–4000 cm−1) at Mansoura University,
Egypt, and in CsI plates on a Magna 850 (200–600 cm−1) at Illi-
nois State University, Normal, USA. The electronic spectra, as Nujol
mull and DMF solution, were recorded on a UV2 Unicam UV/Vis at
Mansoura University, Egypt. The 1H NMR spectra of the ligands, in
d6-DMSO (300 MHz), were recorded on a Varian Gemini Spectrom-
eter at Illinois State University, USA. The magnetic moment values
were evaluated at room temperature (25 1 ◦C) using a Johnson
Matthey magnetic susceptibility balance at Mansoura University,
Egypt. The ESR spectra of the Cu(II) complexes were recorded as
solid at 298 ◦C in a 3 mm pyrex tube on a Bruker EMX Spectrometer
at Illinois State University, USA.
Fig. 1. Formula of the investigated ligands.
filtration, recrystallized from ethanol and dried. The proposed
formula of the ligands (Fig. 1) is in good agreement with the
stoichiometries concluded from their analytical data as well as IR
and 1H NMR data in Table 1. A representative example is the 1H
NMR spectrum of HBP4M (Fig. 2).
Table 1
Name, abbreviation, 1H NMR and IR spectral data of benzophenone thiosemicarbazone derivatives
Ligand
1H NMR signals (ppm)
IR spectral bands (cm−1))
OH
N4H
N2H
OCH3
CH3
CH2
ꢀOH
ꢀN4H
ꢀN2H
ꢀC
N
ꢀC S
2-Hydroxybenzophenone-4-methyl-thiosemicarbazone, HBP4Ma
2-Hydroxybenzophenone-4-phenyl-thiosemicarbazone, HBP4Phb
2-Hydroxybenzophenone-3-pipridyl-thiosemicarbazone, HBPPipa
2-Hydroxy-4-methoxybenzophenone-4-phenylthiosemicarbazone,
HMBP4Phb
10.59
10.38
12.02
10.34
8.41
8.67
–
8.62
10.21
8.24
–
–
–
3.79
3.42
–
–
3.68
–
3344
3295
3348
3317
3323
3295
–
3228
3158
3176
3138
1606
1618
1613
1627
802
787
800
820
–
–
–
8.77
10.29
3264
2-Hydroxy-4-methoxybenzophenone-3-pipridylthiosemicarbazone,
12.94
–
8.11
3.31
–
3.16
3369
–
3150
1625
801
HMBPPipa
a
Solvent for 1H NMR: CDCl3.
Solvent for 1H NMR: d6-DMSO.
b
Fig. 2. 1H NMR spectrum of HBP4M.

A.A. El-Asmy, G.A.A. Al-Hazmi / Spectrochimica Acta Part A 71 (2009) 1885–1890
1887
Table 2
Color, molar conductance and partial elemental analyses of the complexes
a
Complex
Color
ꢁm
% Found (Calcd.)
C
H
N
[Ni(HBP4M-H)(OAc)]
[Ni(HBP4Ph-H)(OAc)]
[Ni(HBPPip-2H)]
[Ni(HMBP4Ph-2H)(H2O)]
[Ni(HMBPPip-H)(OAc]
[Cu(HBP4M-H)(OAc)]
[Cu(HBP4Ph-H)(OAc)]
[Cu(HBPPip-2H)]
Brown
Brown
Green
Brown
Yellowish brown
Dark brown
Olive green
Dark brown
Green
P.S.b
9.2
50.3 (50.8)
56.4 (56.9)
59.7 (59.0)
56.0 (55.8)
54.3 (54.4)
50.8 (50.2)
56.4 (56.2)
56.3 (56.8)
53.1 (53.4)
54.2 (53.8)
4.4 (4.3)
4.5 (4.1)
5.6 (5.1)
3.7 (4.2)
4.7 (5.2)
4.2 (4.2)
3.9 (4.1)
4.4 (5.0)
4.1 (4.5)
4.7 (4.5)
9.9 (10.5)
9.3 (9.1)
10.8 (10.6)
10.0 (9.3)
8.8 (8.6)
10.1 (10.3)
9.3 (9.0)
10.1 (10.5)
8.1 (8.1)
9.0 (8.6)
P.S.b
8.5
9.3
7.1
15.3
P.S.b
13.5
11.2
[Cu(HMBP4Ph-H)(OAc)]H2O
[Cu(HMBPPip-H)(OAc)]
Brown
a
Molar conductance in DMF (ohm−1 cm2 mol−1).
P.S.: partially soluble.
b
Table 3
IR spectral bands of the complexes and their assignments
Compound
ꢀOH
ꢀN4H
ꢀN2H
ꢀC
N
ꢀC N*
ꢀC
S
ꢀM-O
ꢀM-S
ꢀM-N
[Ni(HBP4M-H)(OAc)]
[Ni(HBP4Ph-H)(OAc)]
[Ni(HBPPip-2H)]
[Ni(HMBP4Ph-2H)(H2O)]
[Ni(HMBPPip-H)(OAc]
[Cu(HBP4M-H)(OAc)]
[Cu(HBP4Ph-H)(OAc)]
[Cu(HBPPip-2H)]
3407
3379
3355
3296
–
3287
–
3300
3306
–
3267
–
–
–
–
1573
1576
1572
1609
1604
1573
1562
1571
1606
1600
1600
1599
1598
1569
–
1598
1598
1594
–
–
–
–
–
797
–
–
–
798
786
456
427
433
504
457
409
430
453
482
444
425
406
398
409
421
362
405
419
401
400
382
352
374
362
327
382
375
352
365
327
–
–
–
–
3138
–
–
–
3175
3145
3374
3390
–
[Cu(HMBP4Ph-H)(OAc)]H2O
[Cu(HMBPPip-H)(OAc)]
–
–
–
3. Results and discussion
tance values, in DMF, confirm non-electrolyte compounds
[19].
Nickel(II) and copper(II) complexes of the introduced
ligands have been investigated. According to the prepara-
tive ratio, 1:1 (M:L) stoichiometry is formed (Table 2). The
acetate anion was found coordinated in some complexes
in which all evidence support the proposed formula. Most
isolated solids are soluble in DMF and their molar conduc-
3.1. IR spectra
The IR bands elucidating the coordination sites of the ligands
are included in Table 3. The ligands may coordinate through three
modes.
Fig. 3. The IR spectrum of [Cu(HMBP4Ph-H)(OAc)]H2O.

1888
A.A. El-Asmy, G.A.A. Al-Hazmi / Spectrochimica Acta Part A 71 (2009) 1885–1890
Table 4
Magnetic moments and electronic spectral bands of the compounds
Compound
HBP4M
ꢂeff (BM)
State
Intraligand and charge transfer (cm−1
)
d–d transition (cm−1
)
B (cm−1
)
ˇ
10Dq (cm−1
)
Solid
DMF
Solid
DMF
Solid
DMF
Solid
DMF
Solid
DMF
Solid
DMFa
Solid
DMF
Solid
DMFa
Solid
DMF
Solid
DMF
Solid
DMFa
Solid
DMF
Solid
DMF
Solid
DMF
Solid
DMF
32,670; 30,215; 25,130
33,390; 31,715; 30,990
33,759; 30,455; 26,805; 24,890
32,200; 30,935; 25,600
HBP4Ph
HBPPip
37,760; 29,080; 25,010
33,325; 30,760; 25,240
HMBP4Ph
34,945; 30,515; 28,240; 24,650
33,325; 30,640; 29,985; 27,795
37,880; 33,450; 29,740; 28,540
33,279; 30,035; 25,605; 23,460
34,435; 31,890; 23,990
HMBPPip
[Ni(HBP4M-H)(OAc)]
[Ni(HBP4Ph-H)(OAc)]
[Ni(HBPPip-2H)]
[Cu(HBP4M-H)(OAc)]
[Cu(HBP4Ph-H)(OAc)]
[Cu(HBPPip-2H)]
[Ni(HMBP4Ph-2H)(H2O)]
[Cu(HMBP4Ph-H)(OAc)]H2O
[Ni(HMBPPip-H)(OAc]
[Cu(HMBPPip-H)(OAc)]
0.00
1.55b
0.85c
1.48
1.55
1.16
20,675
24,290; 17,885
17,650; 7,000
1,8075; 7,900
17,650; 10,500
18,005; 6,970
17,770
31,535; 30,755; 26,385
37,340; 29,020; 26,505; 23,515
34,100; 31,835; 26,260; 24,235
34,825; 27,820; 25,370
998
1000
918
0.93
0.93
0.85
0.97
3992
4500
5508
3636
34,585; 26,685; 24,470
33,090; 28,420; 23,510
1039
32,735; 30,690; 28,355; 22,920
35,340; 29,080; 25,130; 21,420
33,690; 29,740; 25,360; 24,580
31,830; 27,285; 24,890; 21,900
30,155; 26,385; 25,550; 24,655
32,130; 26,745; 24,530
18,855
17,650
18,955
17,650
18,075
1.23d
0.81
2.02e
0.98
17,650; 8,385
18,075; 7,910
17,590
18,075
17,945
18,180; 7,910
18,965; 15,195
18,125; 15,010
957
1000
0.92
0.93
4785
4500
31,465; 26,625; 23,750
30,575; 25,370; 24,050
30,640; 25,675; 24,825
35,780; 31,830
26,230; 24,580
35,125; 27,225; 24,410; 21,300
34,170; 30,330; 27,785
–
1006
–
0.94
–
4527
a
Partially soluble in DMF.
Square-planar is 55%.
Square-planar is 75%.
Square-planar is 64%.
b
c
d
e
Square-planar is 41%.
i In [M(HBP4M-H)(OAc)] and [M(HBP4Ph-H)(OAc)], M Cu or Ni,
the ligands act as monobasic tridentate through C N, OH and
C–S by the shifts of ꢀ(C N) and ꢀ(N–N) bands and the appear-
ance of ꢀ(M–N) band at 382–327 cm−1. The thione group is
deprotonated by the disappearance of ꢀ(C S) and the presence
of ꢀ(C N*) and ꢀ(C–S) at 1561–1600 and 726–710 cm−1, respec-
tively. The coordination of C–S is approved by the appearance
of ꢀ(M–S). The shift of ꢀ(OH) is followed by the appearance of
new band at 409 cm−1 attributed to ꢀ(M–O) [20] as shown in
Table 3. Another band located at 504 cm−1 in the spectrum of
[Cu(HBP4M-H)(OAc)]H2O may be due to ꢀ(M–O) of the acetate
group.
Fig. 4. Structure of [Cu(HBP4Ph-H)(OAc)] (A) and [Cu(HMBP4Ph-H)(OAc)] (B).
and ꢀ(C S) bands disappeared with the appearance of bands
due to ꢀ(C N*) and ꢀ(C–S) due to thioenolization at 1598–1569
and 712–720 cm−1, respectively. Strong evidence for nitrogen,
oxygen and sulfur coordination is the appearance of new bands
due to ꢀ(M–N), ꢀ(M–O) and ꢀ(M–S). The broad bands at 3361,
890 and 540 cm−1 in [Ni(HMBP4Ph-2H)(H2O)] are attributed
to ꢀ(OH), ꢃr(H2O) and ꢃw(H2O), respectively, confirming
water coordination [21]; these bands are not observed in the
rest.
ii In [Cu(HMBP4Ph-H)(OAc)]H2O and [M(HMBPPip-H)(OAc)],
M
Cu or Ni, the ligands act also as monobasic tridentate but
through C N, deprotonated OH and C S by the disappear-
ance of ꢀ(OH) and the shifts of ꢀ(C N) and ꢀ(C S) to lower
wavenumbers. The methoxy group which is considered as an
electron donating may increase the electron density on the OH
to become acidic by resonance and facilitates the deprotonation.
Evidence for oxygen, nitrogen and sulfur coordination comes
from the appearance of new bands due to ꢀ(M–O), ꢀ(M–N)
and ꢀ(M–S) (Table 3). The shoulders appearing at 1585–1605
and 1310–1325 cm−1 are due to ꢀas and ꢀs vibrations of the
monodentate acetate [10]. Fig. 3 represents the IR spectrum
of [Cu(HMBP4Ph-H)(OAc)]H2O in the low frequency region
(100–600 cm−1).
Table 5
ESR spectral data of some Cu(II) complexes
Complex
G1 or (g )
g2
g3 (g
)
go
G
||
⊥
[Cu(HBP4M-H)(OAc)]
[Cu(HBP4Ph-H)(OAc)]H2O
[Cu(HBPPip-2H)]
[Cu(HMBPPip-H)(OAc)]
[Cu(HMBP4Ph-H)(OAc)]H2O
2.152
2.134
2.095
2.105
2.102
–
2.046
2.034
2.034
2.029
2.028
–
–
iii In [M(HBPPip-2H)] and [Ni(HMBP4Ph-2H)(H2O)] the ligands act
as dibasic tridentate coordinating through C N, deprotonated
OH and C–S groups. This confirmed from the shift of ꢀ(C N)
to lower wavenumber by 18–42 cm−1 [16]. The N(2)H, hydroxo
2.086
2.047
2.041
2.040
2.088
2.059
2.058
2.055
3.94
2.79
3.62
3.64

A.A. El-Asmy, G.A.A. Al-Hazmi / Spectrochimica Acta Part A 71 (2009) 1885–1890
1889
Fig. 5. The ESR spectrum of [Cu(HBPPip-2H)].
3.2. Magnetic and spectral studies
the Ni(II)-ligand bonds. The values of 10Dq decrease by increasing
the percentage of square-planar participation (Table 4). The spec-
trum of [Ni(HBP4M-H)(OAc)] is different where the strong band at
20,675 cm−1 is attributed to the d–d transition in a square-planar
geometry. In DMF, this band appeared at 24,290 cm−1 indicating a
solvent effect. Fig. 4 presents the structure of [Cu(HBP4Ph-H)(OAc)]
and [Cu(HMBP4Ph-H)(OAc)].
The magnetic moments and the electronic spectral bands of the
studied Ni(II) and Cu(II) complexes are given in Table 4. The ligands
have spectral bands similar in solid and DMF solution and exist at
36,500–25,000 cm−1 corresponding to the ␲→␲ and n→␲ tran-
*
*
sitions [22].
Most of the Ni(II) complexes have subnormal magnetic val-
ues (0.85–2.02 BM) due to mixed stereochemistry of square-planar
and tetrahedral structure. The decrease in the moment values may
be attributed to the presence of square-planar with high percent.
The following complexes are ordered according to the percentage
of square-planar: [Ni(HBPPip-2H)] (75%) > [Ni(HMBP4Ph-2H)]H2O
(64%) > [Ni(HBP4Ph-H)(OAc)] (55%) > [Ni(HMBPPip-H)(OAc)] (41%)
which is calculated by relating the measured values to 3.4 BM (the
tetrahedral Ni(II) complexes have 3.4–3.8 BM range). On the other
hand, [Ni(HBP4M-H)(OAc)] measured zero moment indicative of
totally square-planar structure.
Also, all Cu(II) complexes measured subnormal values
(0.81–1.55 BM) indicating interaction between the copper centers;
the interaction becomes strong in [Cu(HMBP4Ph-H)(OAc)]H2O and
less in [Cu(HBP4Ph-H)(OAc)]; this may be related to the bulky of
HMBP4Ph rather than HBPP4Ph.
3.3. ESR spectra
To obtain further information about the stereochemistry of the
complexes, ESR spectra were recorded and their spin Hamiltonian
parameters were calculated (Table 5). The room temperature solid
state have ESR spectra (Fig. 3) quite similar and exhibit g-tensor
parameters with g > g > 2.0023 indicating that the copper site
||
⊥
2
has a dx2 − dy ground state [25] characteristic for a square-planar
geometry [26].
In axial symmetry, G = (g –2)/(g –2) where G is the exchange
||
⊥
interaction parameter. The calculated G values (Table 4) of the Cu(II)
complexes are lower than 4 suggesting copper–copper exchange
interactions [27]. The band corresponding to the forbidden mag-
netic dipolar transition is not observed at half-field (ca. 1600G,
g = 4.0) indicating mononuclear complexes [28]. The ESR spectrum
of [Cu(HBPpip-2H)] is shown in Fig. 5.
The solution and solid electronic spectra of the complexes are
approximately the same; changes are recorded with the spectra of
their ligands. The band at 22,000–26,000 cm−1 in the spectra of
Cu(II) complexes may be due to LMCT [23].
References
The electronic spectra of the Cu(II) complexes showed one
[1] G.H. Van Giessen, J.A. Crim, D.H. Petering, J. Natl. Cancer Inst. 51 (1973) 139.
[2] V. Sharma, V. Sharma, R. Bohra, J.E. Drake, M.B. Hursthouse, M.E. Light, Inorg.
Chim. Acta 360 (2007) 2009.
[3] A.A. El-Asmy, Y.M. Shaibi, I.M. Shedaiwa, M.A. Khattab, Synth. React. Inorg. Met.
Org. Chem. 18 (4) (1988) 331.
[4] L.R. Thompson, D. Jeanette, B.P. Russell, H.G. Hitchings, Proc. Soc. Exp. Biol. Med.
84 (1953) 496.
[5] E. Franco, E. Lopez-Torres, M.A. Mendiola, M.T. Sevilla, Polyhedron 19 (2000)
441.
[6] D.W. Maragerum, G.D. Owens, Metal Ions in Biological Systems, Marcel Dekker,
New York, 1981.
[7] G.A.A. Al-Hazmi, M.S. El-Shahawi, A.A. El-Asmy, Transition Met. Chem. 30
(2005) 464.
[8] G.A.A. Al-Hazmi, N.M. El-Metwally, O.A. Al-Gammal, A.A. El-Asmy, Spec-
trochim. Acta A 69 (2008) 54.
[9] R.M. El-Shazly, G.A.A. Al-Hazmi, S.E. Ghazy, M.S. El-Shahawi, A.A. EI-Asmy,
Coord. Chem. 59 (8) (2006) 846.
band at 17,650–18,965 cm−1, in solid state, corresponding to the
2
2B1g→ Eg transition in a square-planar geometry [24]. In DMF
solution, this band is shifted to higher energy suggesting a weak
interaction with the solvent.
The spectra of Ni(II) complexes, in Nujol, showed three bands at
23,515–24,530, 17,650–18,180 and 70,000–10,500 cm−1 assignable
to the d–d transitions. The first band may be due to the transi-
tion in a square-planar geometry while the others are attributed to
the 3T1→ T1 (P) (␯3) and 3T1→ A2 (␯2) transitions in a tetrahedral
structure (in DMF solution, the first band is observed at high energy
indicating strong interaction with the solvent). The ligand field
parameters (B, ˇ and 10Dq) calculated for the complexes in Nujol
and DMF solutions are presented in Table 4 according to the tetra-
hedral Ni(II) equations and found lower than those reported for the
suggested structure. The values of ˇ indicate an ionic character for
3
3
[10] R.M. El-Shazly, G.A.A. Al-Hazmi, S.E. Ghazy, M.S. El-Shahawi, A.A. El-Asmy,
Spectrochim. Acta A 61 (2005) 243.
[11] P. Bindu, M.R.P. Kurup, Ind. J. Chem. 38A (1999) 388.

1890
A.A. El-Asmy, G.A.A. Al-Hazmi / Spectrochimica Acta Part A 71 (2009) 1885–1890
[12] R.P. John, A. Sreekanth, M.R.P. Kurup, S.M. Mobin, Polyhedron 21 (2002) 2515.
[13] A.A. Nassar, F.A. El-Saied, M.I. Ayad, D.X. West, Transition Met. Chem. 24 (1999)
617.
[14] A.A. El-Asmy, Y.M. Shaibi, I.M. Shedaiwa, M.A. Khattab, Synth. React. Inorg. Met.
Org. Chem. 20 (4) (1990) 461.
[15] D.X. West, Y.H. Yang, T.L. Klein, K.I. Goldberg, A.E. Liberta, J. Martinez, S. Ortega,
Polyhedron 14 (1995) 1681.
[16] G.A. Bain, D.X. West, J. Krecji, J. Martinez, S. Ortega, R.A. Toscano, Polyhedron
16 (1997) 855.
[17] D.X. West, A.A. Nassar, F.A. El-Saied, M.A. Ayad, Transition Met. Chem. 23 (1998)
321.
[18] S.D. Dhumwad, K.B. Gudasi, T.R. Goudar, Ind. J. Chem. 33A (1994) 320.
[19] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81.
[21] A.A. El-Asmy, M.A. Hafez, E.M. Saad, F.T. Taha, Transition Met. Chem. 19 (1994)
603.
[22] P.N. Yadav, M.A. Demertzis, D. Demertzi, S. Skoulika, D.X. West, Inorg. Chem.
Acta 349 (2003) 30.
[23] A.A. El-Asmy, M.E. Khalifa, M.M. Hassanian, Synth. React. Inorg. Met. Org. Chem.
31 (2001) 1787.
[24] H.T.M. Tarafder, K. Chew, A.K. Crouse, M.A. Ali, M.B. Yamin, K.H. Fun, Polyhedron
21 (2002) 2683.
[25] G. Speie, J. Csihony, A.M. Whalen, C.G. Pie-pont, Inorg. Chem. 35 (1996) 3519.
[26] J.L. Mesa, J.L. Pizarro, M.I. Arriortua, Cryst. Res. Technol. 33 (1998) 489.
[27] V.T. Kasumo, Spectrochim. Acta 57A (2001) 1649.
[28] (a) J.A. Wellman, F.B. Hulsbergen, J. Inorg. Nucl. Chem. 40 (1978) 143;
(b) U. Sagakuchi, A.W. Addison, J. Chem. Soc. Dalton Trans. 660 (1979).
[20] P. Souza, F. Kaiser, J.R. Moguer, A. Arquero, Transition Met. Chem. 12 (1987) 128.