The influence of the methyl substituents at C2 carbon of thiosemicarbazones {R1R2C2=N3-N 2H-C1(=S)N1H2} on bonding and structures of copper(I) complexes

Article abstract of DOI:10.1002/zaac.200700199

Reaction of copper(I) halides with acetone thiosemicarbazone (Hactsc) and acetaldehyde thiosemicarbazone (Hmtsc) in CH₃CN in the presence of PPh₃ has formed dimeric complexes of type, [Cu₂(μ-X) ₂(η¹-S-HtSc)₂(Ph₃P) ₂] (Htsc: X; Hmtsc, Br, 1; I, 2; Hactsc, I, 3; Cl, 5), and a monomer, [CuBr((η¹S-Hactsc)(Ph₃P)₂ (4). The complexes have been characterized using analytical data, spectroscopy and X-ray crystallography (1-4). The presence of methyl substituents at C² carbon of thiosemicarbazone seems to alter inter- and intra-molecular hydrogen bonding. Intermolecular and intramolecular interactions by amino and imino hydrogen atoms respectively with bridging halogen atom shorten X-Cu-X bond angle, and open up Cu-X-Cu bond angle, resulting in longer Cu...Cu separation (3.50-3.61 A) in complexes 1-3.

Full text of DOI:10.1002/zaac.200700199

DOI: 10.1002/zaac.200700199
The Influence of the Methyl Substituents at C2 Carbon of Thiosemicarbazones
{R1R2C2؍N3-N2H-C1(؍S)N1H2} on Bonding and Structures of Copper(I)
Complexes
Tarlok S. Lobana*,a, Sonia Khannaa, and Ray J. Butcherc
a Amritsar / India, Department of Chemistry, Guru Nanak Dev University
b Washington DC / USA, Department of Chemistry, Howard University
Received April 23rd, 2007.
th
˜
Dedicated to Professor Alfonso Castineiras on the Occasion his 65 Birthday
Abstract. Reaction of copper(I) halides with acetone thiosemicar-
bazone (Hactsc) and acetaldehyde thiosemicarbazone (Hmtsc) in
CH3CN in the presence of PPh3 has formed dimeric complexes of
type, [Cu2(µ-X)2(η1-S-Htsc)2(Ph3P)2] (Htsc: X; Hmtsc, Br, 1; I, 2;
Hactsc, I, 3; Cl, 5), and a monomer, [CuBr((η1-S-Hactsc)(Ph3P)2
(4). The complexes have been characterized using analytical data,
spectroscopy and X-ray crystallography (1Ϫ4). The presence of
methyl substituents at C2 carbon of thiosemicarbazone seems to
alter inter- and intra-molecular hydrogen bonding. Intermolecular
and intramolecular interactions by amino and imino hydrogen
atoms respectively with bridging halogen atom shorten XϪCuϪX
bond angle, and open up CuϪXϪCu bond angle, resulting in
˚
longer Cu···Cu separation (3.50Ϫ3.61 A) in complexes 1Ϫ3.
Keywords: Copper; Acetone thiosemicarbazone; Acetaldehyde
thiosemicarbazone
Introduction
Thiosemicarbazone(I) derivatives of transition and main
group metals have gained attention in view of their interest-
ing bonding behaviour as well as their applications in other
fields such as pharmaceutical, biological and analytical
[1Ϫ10]. Thiosemicarbazone chemistry of copper(I) has re-
ceived attention only recently [11Ϫ13], unlike copper(II)
Chart 1
Experimental Section
which has been intensively investigated [1Ϫ4]. For R1
ϭ
Materials and techniques
pyridyl, R2 ϭ H, and R1 ϭ R2 ϭ Ph, only tetrahedral
monomers [CuX(Htsc)(PPh3)2] (X ϭ Cl, Br, I), for R1 ϭ
Ph, R2 ϭ H,both monomers (X ϭ I) and dimers (X ϭ Br,
Cl), and for R1 ϭ furan, thiophene and pyrrole, R2 ϭ H,
both halogen bridged [Cu2(µ-I)2(η1-S-Htsc)2(PPh3)2] and
sulfur bridged dimers [Cu2(µ-S-Htsc)2X2(PPh3)2] (X ϭ Br,
Cl) have been isolated [12, 13].Further, acetone thiosemicar-
bazone (R1 ϭ R2 ϭ Me) with copper(I) chloride has formed
a tetramer [Cu4(Htsc)4Cl4], and a monomer [Cu(Htsc)2]Cl
[11], along with its complexes with other metals [14].
In this paper, both the substituents at C2 carbon have
been varied (Chart 1), and reactions carried out with cop-
per(I) halides. The products have been characterized using
analytical data, spectroscopy, and x-ray crystallography
(1Ϫ4).
Copper(I) halides were prepared by reducing an aqueous solution
of CuSO4 ·5H2O with SO2in the presence of NaX (X ϭ Cl, Br, I)
in H2O [12]. Ph3P was procured from Aldrich Chemicals Ltd. and
used as such. Acetone thiosemicarbazone (Hactsc) was prepared
by the literature method [11], and acetaldehyde thiosemicarbazone
(Hmtsc) was prepared by refluxing thiosemicarbazide with acet-
aldehyde in methanol for 5-6 hours. C, H and N analysis were
obtained with Thermoelectron FLASHEA1112 CHNS analyzer.
Infrared spectra were recorded as KBr pellets in the range
4000Ϫ200 cmϪ1 on PyeϪUnicam SP-3-300 spectrophotometer.
The melting points were determined with a Gallenkamp electrically
1
heated apparatus. H NMR were recorded on a JEOL AL-300 FT
spectrometer operating at a frequency of 300 MHz using CDCl3 as
solvent with TMS as the internal reference. 31P NMR spectra were
recorded on a Bruker ACP-300 spectrometer operating at a fre-
quency of 121.5 MHz with (CH3O)3P as the external reference set
at zero value.
* Prof. T. S. Lobana
India,Department of Chemistry, Guru Nanak Dev Universit
Amritsar Ϫ 143 005 / India
Fax: 91-183-2-258820
E-mail: tarlokslobana@yahoo.co.in
Synthesis of the complexes
[Cu2(µ-Br)2(η1-S-Hmtsc)2(Ph3P)2] (1). To a stirred solution of CuBr
(0.025 g, 0.174 mmol) in 10 mL CH3CN was added solid PPh3
(0.046 g, 0.174 mmol), and the stirring was continued until the for-
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Influence of the Methyl Substituents at C2 Carbon of Thiosemicarbazones
IR (KBr, Nujol, cmϪ1): ν(N-H) 3398s, 3271b (-NH2-), 3143b (-NH-); ν(Cϭ
N) ϩ δNH2 ϩ ν(CϭC) 1569s, 1517s ν(C-S)ϩ ν(C-N) 1000s, 742s (thioamide
moiety); ν(P-CPh) 1095s. 1H NMR (CDCl3, δ) 2.17, 2.01 (d, -CH3); 6.91 (s, -
N1H2); 7.29Ϫ7.67 (m, -PPh3 ϩ -N1H2), 10.20 (s, -N2H). 31P NMR (CDCl3,
δ): Ϫ111.10, ∆δ(δcomplex Ϫ δligand) ϭ 2.05.
mation of white solid. To this solid suspended in CH3CN, was ad-
ded Hmtsc ligand (0.020 g, 0.174 mmol) and the solution was
further stirred for a period of 1 h. Yellow crystals formed by the
slow evaporation of the solution were separated. Mp. 178Ϫ180 °C,
yield 64 %. Anal. calcd. C42H44Br2Cu2N6P2S2 (1045.9); C 48.19
(calc. 48.60); H 4.21 (4.97); N8.03 (7.79) %.
IR (KBr, Nujol, cmϪ1): ν(N-H) 3460s, 3348s (-NH2-), 3148b (-NH-); ν(Cϭ
N) ϩ δNH2 ϩ ν(CϭC) 1578m,1556m; ν(C-S)ϩ ν(C-N) 1069s, 998s, 881s
(thioamide moiety); ν(P-CPh) 1098s. 1H NMR (CDCl3, δ) 1.92 (d, -CH3);
5.97, 6.85 (sb, -N1H2); 7.24Ϫ7.37 (m, -PPh3); 7.60, 7.88 (q, -CH), 11.62 (s, -
N2H). 31P NMR (CDCl3, δ): Ϫ111.68, ∆δ (δcomplex Ϫ δligand) ϭ 1.47.
[Cu2Cl2(η1-S-Hactsc)2(Ph3P)2] (5). To a stirred solution of CuCl
(0.025 g, 0.25 mmol) in 10 mL CH3CN, was added solid PPh3
(0.066 g, 0.25 mmol) and the stirring was continued until the for-
mation of a white solid. To this solid suspended in CH3CN, was
added Hactsc ligand (0.033 g, 0.25 mmol), and the solution was
further stirred for a period of 1 h. White crystals were formed by
the slow evaporation of the solution. Mp. 190Ϫ192 °C, yield, 55 %.
Anal. calcd. C44H48Cu2Cl2N6P2S2 (983.98); C 53.87 (calc. 53.65);
H 4.60 (4.88); N8.62 (8.53) %.
IR (KBr, Nujol, cmϪ1): ν(N-H) 3450s, 3260s (-NH2-), 3130m (-NH-); ν(Cϭ
N) ϩ δNH2 ϩ ν(CϭC) 1620s, 1560s, 1470s; ν(C-S)ϩ ν(C-N) 1050s, 858s,
742s (thioamide moiety); ν(P-CPh) 1097s. 1H NMR (CDCl3, δ) 2.19, 2.03 (s, -
CH3); 7.34Ϫ7.51 (m, PPh3 ϩ N1H2). 31P NMR (CDCl3, δ): Ϫ111.07,
∆δ(δcomplex Ϫ δligand) ϭ 2.08.
Complexes 2 and 3 were prepared similarly.
[Cu2(µ-I)2(η1-S-Hmtsc)2(Ph3P)2] (2). Mp. 185Ϫ187 °C, yield, 71 %.
Anal. calcd. C42H44Cu2I2N6P2S2 (1139.77); C 44.83 (calc. 44.22);
H 4.08 (3.86); N 7.62 (7.36) %.
IR (KBr, Nujol, cmϪ1): ν(N-H) 3458s, 3340s (-NH2-), 3155b (-NH-); ν(Cϭ
N) ϩ δNH2 ϩ ν(CϭC) 1574m,1526m, 1433s; ν(C-S)ϩ ν(C-N) 1030s, 810s,
745s (thioamide moiety); ν(P-CPh) 1095s. 1H NMR (CDCl3, δ) 1.98 (d, -
CH3); 6.97 (sb, -N1H2); 7.26Ϫ7.50 (m, -PPh3); 7.78 (q, -CH), 11.21 (s, -N2H).
31P NMR (CDCl3, δ): Ϫ114.04, ∆δ(δcomplex Ϫ δligand) ϭ Ϫ0.9.
X-ray crystallography
The suitable light yellow crystals of compounds 1-4 were mounted
on an automatic Enraf Nonius CAD-4 diffractometer equipped
with the graphite monochromator and MoϪKα radiation (λ ϭ
[Cu2I2(η1-S-Hactsc)2(Ph3P)2] (3). Mp. 190Ϫ192 °C, yield, 72 %.
Anal. calcd. C44H48Cu2I2N6P2S2 (1167.82); C 44.87 (calc. 45.21);
H 3.92 (4.11); N6.97 (7.19) %.
IR (KBr, Nujol, cmϪ1): ν(N-H) 3460s, 3342 s, 3207s (-NH2-), 3199b (-NH-);
ν(CϭN) ϩ δNH2 ϩ ν(CϭC) 1568s, 1504s, 1477s; ν(C-S)ϩ ν(C-N) 1000s,
858s (thioamide moiety); ν(P-CPh) 1095s. 1H NMR (CDCl3, δ) 2.17, 2.00
(d, -CH3); 7.20 (sb, -N1H2); 7.28Ϫ7.55 (m, -PPh3 ϩ -N1H2). 31P NMR
(CDCl3, δ): Ϫ78.44, ∆δ(δcomplex Ϫ δligand) ϭ 34.71.
˚
0.71073 A). The unit cell dimensions and the intensity data were
measured at 93 K for 1, 2, 4 and 173 K for 3. The structures were
solved by direct methods and refined by the full matrix least
squares method based on F2. All the nonhydrogen atoms were re-
fined anisotropically using XCAD-49 (data reduction) and
SHELXL. The hydrogen atoms were calculated using structure fac-
tor calculations in their idealized positions. The crystallographic
data is summarized in Table 1.
[CuBr(η1-S-Hactsc)(Ph3P)2] (4). To a stirred solution of CuBr
(0.025 g, 0.174 mmol) in 10 mL CH3CN was added solid ligand
Hactsc (0.023 g, 0.174 mmol) followed by stirring for 1 h, resulting
in the formation of a white solid. To this solid, was added solid
PPh3 (0.092 g, 0.34 mmol). The solution was further stirred for a
period of 1 h. Pale yellow crystals were formed by the slow evapor-
ation of the solution. Mp. 176Ϫ178 °C yield, 70 %. Anal. calcd.
C42H44Br2Cu2N6P2S2 (799.19); C 60.56 (calc. 60.06); H 4.55 (4.88);
N4.96 (5.25) %.
Results and Discussion
Synthesis and infrared spectroscopy
Reaction of a copper(I) halide with PPh3 in 1:1molar ratio
in CH3CN forms a white solid and the addition of a thiose-
Table 1 Crystallographic data for compounds 1, 2, 3 and 4
1
2
3
4
Empirical formula
M.Wt.
C42H44Br2Cu2N6P2S2
1045.79
0.56 x 0.45 x 0.10
1.89Ϫ28.25
C42H44I2Cu2N6P2S2
1139.77
0.34 x 0.20 x 0.10
1.89Ϫ28.60
Semi-empirical from equivalents
monoclinic
P21/n
C40H39BrCuN3P2S
799.19
0.35 x 0.34 x 0.09
1.87Ϫ29.59
C44H48Cu2I2N6P2S2
1167.82
0.48 x 0.35 x 0.25
1.84Ϫ28.33
Crystal size /mm
Theta range /°
Absorption correction
Crystal system
Space group
monoclinic
P21/n
9.110(7)
17.640(13)
13.581(10)
2180(3)
triclinic
monoclinic
P21/n
9.3265(11)
18.222(2)
13.5853(16)
2305.6(5)
¯
P1
˚
a /A
9.222(2)
10.6105(14)
12.4643(16)
15.7427(19)
1817.3(4)
98.893(2)
101.021(2)
113.139(2)
2
1.460
1.879
13923
8451, 0.0738
0.0423,
˚
b /A
17.867(5)
13.521(4)
2226.8(10)
˚
˚
c /A
3
V(A )
α (°)
β (°)
92.804(13)
91.778(5)
92.995(5)
γ (°)
Z
2
2
2
D /Mg mϪ3
1.593
3.016
13749
5043, 0.0324
0.0658, 0.1387
1.700
2.545
16991
5403, 0.0491
0.0488, 0.1038
1.682
2.460
22662
6370, 0.0526
0.0462,
0.1004
µ(Mo Kα) /(mmϪ1
)
Reflns. collected
Independent reflns., Rint
Final R indices
R1
wR2
0.1102
Z. Anorg. Allg. Chem. 2007, 1820Ϫ1826
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www.zaac.wiley-vch.de
1821

T. S. Lobana, S. Khanna, R. J. Butcher
˚
micarbazone yields dimeric complexes of the type,
[Cu2X2(Htsc)2(PPh3)2] (1Ϫ3, 5) (Scheme 1). Direct reaction
of copper(I) bromide with Hactsc in the presence of two
moles of PPh3 has formed a monomeric tetrahedral com-
plex, [CuBr(Hactsc)(PPh3)2] 4. All these complexes have
melting points in the range of 178Ϫ192 °C and are readily
soluble in chloroform except 5 which is sparingly soluble.
Table 2 Selected bond lengths /A and bond angles /° for com-
pounds 1Ϫ4
1
CuϪP
CuϪS
CuϪBr
2.252(2)
2.318(2)
2.4724(2)
2.7191(2)
SϪC(3A)
N(1A)ϪN(2A)
Cu···Cu
1.677(8)
1.440(8)
3.511(2)
CuϪBrϪCu
84.96(5)
SϪCuϪBr
117.33(7)
110.66(6)
95.04(5)
PϪCuϪS
PϪCuϪBr
110.92(6)
102.05(5)
118.14(6)
BrϪCuϪBr#1
2
CuϪP
CuϪS
CuϪI
IϪCu
2.2522(2)
2.3098(2)
2.6324(8)
2.8202(1)
SϪC(3)
N(1)ϪN(2)
1.679(6)
1.415(7)
Cu···Cu
3.606(1)
CuϪIϪCu#1
PϪCuϪS
82.72(3)
110.96(5)
PϪCuϪI#1
SϪCuϪI
103.12(4)
111.08(5)
117.58(5)
97.28(3)
PϪCuϪI
114.91(4)
IϪCuϪI#1
3
Scheme 1
CuϪP
CuϪS
CuϪI
IϪCu
CuϪIϪCu#1
PϪCuϪS
2.2510(1)
2.3017(2)
2.6130(7)
2.8020(8)
SϪC(1)
N(2)ϪN(3)
Cu···Cu
1.656(6)
1.437(6)
3.5043(0)
The IR spectra of complexes (1Ϫ5), reveal the presence
of ν(N-H) bands in the ranges, 3460Ϫ3270 cmϪ1 (due to -
NH2 group), and 3143Ϫ3155 cmϪ1 (due to -NH- group).
Further, δ(NH2), ν(CϭN) and ν(CϭC) bands, shift to the
lower energy region, 1568Ϫ1433 cmϪ1 relative to the free
ligands in the range, 1643Ϫ1512 cmϪ1. Similarly, thioamide
bands appear in the range, 1000Ϫ742 cmϪ1, shifting to
lower energy region in complexes relative to the free ligands
(1087Ϫ865 cmϪ1). A characteristic ν(P-CPh) band in the re-
gion 1095Ϫ1098 cmϪ1 supports the presence of the PPh3 in
the complexes [15].
80.57(2)
110.58(6)
PϪCuϪI#1
SϪCuϪI
104.45(4)
116.52(5)
109.26(5)
99.43(2)
PϪCuϪI
115.11(4)
IϪCuϪI#1
4
CuϪP(1)
CuϪP(2)
CuϪS
2.279(1)
2.267(1)
2.373(1)
CuϪBr
SϪC(1)
2.475(1)
1.710(3)
P(2)ϪCuϪP(1)
P(2)ϪCuϪS
P(1)ϪCuϪS
120.11(3)
104.35(3)
109.41(3)
P(1)ϪCuϪBr
P(2)ϪCuϪBr
SϪCuϪBr
103.19(2)
110.11(2)
109.51(2)
Crystal Structures of the Dimers 1؊3
The atomic numbering schemes for the molecular structures
of complexes 1Ϫ3 are shown in figures 1Ϫ3, respectively,
and the selected bond lengths and angles are given in
Table 2. These complexes (1Ϫ3) crystallized in the mono-
clinic space group, P21/n.
In complex 1, the copper atom is bonded to one Br
atom, one P atom from PPh3 ligand, and one S atom of the
Hmtsc ligand forming
a
three coordinated unit
{CuBr(PPh3)(Hmtsc)}, and two such units dimerize
via bromine atoms to form a bromo-bridged dimer
[Cu2(µ-Br)2(η1-S-Hmtsc)2(PPh3)2] (1), with a terminally
bonded Hmtsc ligand (Figure 1). The central Cu2Br2 core
forms a parallelogram with two unequal CuϪX bond dis-
˚
tances, 2.4724(2) and 2.7191(2) A, which are slightly longer
˚
than 2.485(1), 2.575(1) A, in the analogous bromo-bridged
dimer, [Cu2(µ-Br)2(η1-S-Hbtsc)2(PPh3)2] [12]. Further, the
CuϪS and CuϪP bond distances of 2.318(2) and
˚
2.252(2) A are similar to those found in the literature [12,
13, 16]. PPh3 and S bonded ligands occupy trans positions
across the central Cu(µ-Br)2Cu core.
The iodide-bridged dimers 2 and 3 (Figure 2 and 3) have
similar structures with bond parameters of CuϪP,
Figure 1 Molecular structure of
[Cu2(µ-Br)2(η1-S-Hmtsc)2(Ph3P)2] (1)
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 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2007, 1820Ϫ1826

Influence of the Methyl Substituents at C2 Carbon of Thiosemicarbazones
˚
Table 3 Selected bond angles /° and bond distance /A of com-
pounds 1Ϫ3 and related dimeric complexes.
Complex Ligand
R1, R2
CuϪXϪCu
XϪCuϪX
95.04(5)
Cu···Cu Hydrogen
bonding
1
CH3, CH3 84.96(5)
CH3, CH3 82.72(3)
CH3, CH3 80.57(2)
3.511(2) N2H···Br
N1H···Bra)
2
97.28(3)
3.606(1) N2H···I
N1H···Ia)
3
99.43(2)
3.5043(0) N2H···I
N1H···Ia)
b)
b)
6 [12]
7 [12]
Ph, H
74.22(2)
105.78(2)
112.001(1)
3.0543(1) N1H···Br
N2H···S
67.999(2)
3.9808(8) N1H···I
N2H···S
b)
8[12]
75.586(1)
70.72(7)
104.414(1)
109.28(7)
3.2247(6) N1H···I
N2H···S
b)
9 [13]
3.097(4) N1H···I
N2H···Sa)
a) intermolecular hydrogen bonding
Figure 2 Molecular structure of [Cu2(µ-I)2(η1-S-Hmtsc)2(Ph3P)2] (2)
b) [Cu2(µ-Br)2(Hbtsc)2(PPh3)2] (R1 ϭ Ph, R2 ϭ H, Hbtsc ϭ benzal-
dehyde thiosemicarbazone) 6, [Cu2(µ-I)2(Hftsc)2(PPh3)2] (R1 ϭ fu-
ran, R2 ϭ H, Hftsc ϭ furancarbaldehyde thiosemicarbazone) 7,
[Cu2(µ-I)2(Httsc)2(PPh3)2] (R1 ϭ thiophene, R2 ϭ H, Httsc ϭ thio-
phenecarbaldehyde thiosemicarbazone) 8 [12], [Cu2(µ-I)2(Hptsc)2-
(PPh3)2] (R1 ϭ Pyrrole, R2 ϭ H, Hptsc ϭ pyrrolecarbaldehyde
thiosemicarbazone) 9 [13]
Table 4 Selected bond angles /° of compound 4 and related com-
pounds.
Complex Ligand
R1, R2
PϪCuϪP PϪCuϪBr SϪCuϪBr PϪCuϪS Hydrogen
bonding
4
CH3, CH3 120.11(3) 110.11(2), 109.51(2) 104.35(3), N2H···Br
103.19(2) 109.41(3) CH3···Br
10 [15] a) Ph, Ph
11 [12] a) Ph, H
12 [12] a) py, H
131.56(4) 105.27(6), 112.38(4) 103.34(4), N1H···Br
99.49(6) 99.49(6)
123.31(2) 107.21(2), 109.93(2) 106.73(2), N1H···Br
104.61(2) 104.73(2)
122.39(5) 106.40(4), 107.76(4) 104.22(5), N1H···Br
105.11(4) 110.24(5)
a) [CuBr(Hbztsc)(PPh3)2] (10) {Hbztsc
thiosemicarbazone} [15], [CuBr(Hbtsc)(PPh3)2] (11) {Hbtsc ϭ Benzal-
dehyde thiosemicarbazone} [12] and [CuBr(Hpytsc)(PPh3)2] (12) [12]
ϭ
Benzophenone
Figure 3 Molecular structure of [Cu2(µ-I)2(η1-S-Hactsc)2(Ph3P)2] (3)
˚
˚
˚
2.251Ϫ2.252 A; CuϪS, 2.302Ϫ2.310 A and CuϪI,
2.613Ϫ2.820 A. The angles around each copper atom lie in
intramolecularϪN2H···X (X ϭ Br 1; I 2, 3) hydrogen bond-
ing, while one of the amino hydrogen atom forms the inter-
molecular ϪHN1H···X hydrogen bonds with one of the
bridging halogen atom (Table 5) to form a polymeric chain
(Figures 4Ϫ6).
the range, 80.57Ϫ118° for 1Ϫ3 revealing a distorted tetra-
hedral geometry about each copper atom. The stoichi-
ometry of compound 5 suggests a halogen bridged dimeric
structure.
The packing arrangement of the dimers 1Ϫ3, reveal that
the imino hydrogen atoms are engaged in the
Table 3 shows a comparison of the CuϪXϪCu and
XϪCuϪX bond angles within Cu(µ-X)Cu core in com-
Z. Anorg. Allg. Chem. 2007, 1820Ϫ1826
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1823

T. S. Lobana, S. Khanna, R. J. Butcher
˚
Table 5 Hydrogen bonds (in A) of compounds 1؊4
DϪH···A
d(H···A)
d(D···A)
<(DHA)
1
N(2A)-H(2AB)···Br
2.68
2.93
3.551(6)
3.660(6)
169.8
142.1
N(3A)-H(3AB)···Br#2
2
N(2)-H(2B)···I
2.76
2.94
3.638(5)
3.671(5)
172.9
142.0
N(3)-H(3B)···I#2
3
Figure 6 Packing diagram of [Cu2(µ-I)2(η1-S-Hactsc)2(Ph3P)2] (3)
N(2)-H(2A)···I
2.91
3.01
3.755(5)
3.696(5)
162.9
136.0
N(1)-H(1B) ···I#2
4
plexes 1Ϫ3, and the analogous halogen bridged dimers
6Ϫ9. These comparisons reveal that in compounds 1Ϫ3,
the CuϪXϪCu bond angle is the largest, while the
XϪCuϪX bond angle is the shortest versus that in the di-
mers 6Ϫ9. Complexes exhibit intramolecular (X ϭ Br 1,
I 2, 3) and ϪHN1H···X intermolecular hydrogen bonding
interactions. This is in contrast to the related dimers 6Ϫ9,
which exhibited ϪHN1H···X hydrogen bonding (Chart-2).
The presence of methyl substituents at C2 carbon of acetone
thiosemicarbazone and acetaldehyde thiosemicarbazone
seems to play an important role in the orientation of amino
hydrogen atoms trans to the bridging halogen atoms
thereby altering the nature of the inter or intramolecular
hydrogen bonding. This behaviour is similar to that found
in the analogous halogen bridged dimers, [Cu2(µ-X)2-
(Htsc)2(PPh3)2] (X ϭ Cl, Br; Htsc ϭ acetophenone thiosem-
icarbazone, R1 ϭ Me, R2 ϭ Ph) [16]. The copper-copper
N(2)-H(2A)···Br
2.62
2.52
3.484(2)
3.373(2)
167.2
163.3
N(1)-H(1B)···S#2
˚
The pre-fixed d(D-H) distance is 0.88 A.
˚
separation lies in the range 3.50Ϫ3.61 A, which shows lack
of any Cu···Cu interaction as this distance is much longer
than twice the sum of van der Waals radius of copper,
˚
2.80 A [17]. This longer separation may be due to simul-
taneous pulling of one of the bridging halogen atom by the
imino as well as the amino hydrogen atoms which shortens
CuϪXϪCu bond angle and opens up XϪCuϪX bond an-
gle. It has been analyzed in a related study on copper-het-
erocyclic thioamide dimers that a bigger angle at Cu is ac-
companied by smaller angle at X and this leads to longer
X···X distance [18]. In the present case, the Br···Br distance
˚
is 3.815(2) A in complex 1 and I···I distances are 4.08(2)
˚
and 4.122(2) A in 2 and 3, respectively. These distances are
longer than twice the sum of van der Waals radius of bro-
˚
˚
mine (3.80 A) and iodine (4.06 A) with no possible interac-
tion [17].
Figure 4 Packing diagram of [Cu2(µ-Br)2(η1-S-Hmtsc)2(Ph3P)2] (1)
Chart 2
Crystal structure of the monomer 4
Complex [CuBr(Hactsc)(PPh3)2] (4) crystallized in triclinic
space group and in this complex, each copper atom is
Figure 5 Packing diagram of [Cu2(µ-I)2(η1-S-Hmtsc)2(Ph3P)2] (2)
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Z. Anorg. Allg. Chem. 2007, 1820Ϫ1826

Influence of the Methyl Substituents at C2 Carbon of Thiosemicarbazones
are analogous to the literature values [12, 15]. The geometry
about copper atom is a distorted tetrahedral with the bond
angles in the range, 104Ϫ121°. The PϪCuϪP bond angle
is the largest while PϪCuϪS is the smallest bond angle.
The packing diagram of complex 4 (Figure 8) reveals that
each bromine atom is engaged in the intramolecular hydro-
gen bonding with the imino hydrogen atom (-N2H···Br),
and one of the hydrogen atoms of methyl group
(-H2CH···Br) (chart-2). One of the amino hydrogen is in-
volved in the intermolecular hydrogen bonding with S atom
(-N1H···S) forming a hydrogen bonded dimer.
A comparison of selected bond angles of complex 4 with
the related monomeric complexes is given in Table 4. It can
be seen that for 4, PϪCuϪP bond angle (120.11(3)°) is the
largest and P(1)ϪCuϪBr bond angle (110.11(2)°) is the
shortest, among all the related monomeric complexes with
copper(I) bromide (10Ϫ12). Strong intramolecular interac-
tions by imino hydrogen (N2H···Br, 2.62) as well as by
methyl hydrogen in 4 appears to increase P(1)ϪCuϪBr
bond angle, with simultaneousdecrease in PϪCuϪP bond
angle. In contrast, halogen atoms are engaged in the intra-
molecular ϪN1H2···X (6, 7), and N2H···X hydrogen bond-
ing in compound 12.
Figure 7 Molecular structure of [Cu Br(η1-S-Hactsc)(Ph3P)2] (4)
Spectroscopic Studies
1
The H NMR spectra of complexes 1Ϫ5 in CDCl3 reveal a
down field shift of diagnostic signal due to hydrazinic N2H
proton in the range, ca. δ 10.20Ϫ11.62 versus the ligands
(δ 9.04Ϫ9.87 [11]), confirming the coordination of thiosem-
icarbazones as neutral ligands. Further, amino -N1H2 pro-
tons showed a pair of signals at δ 5.97 and 6.85 for com-
pound 1, anda single signal in the range, ca. δ 6.91Ϫ7.20
for other compounds 2Ϫ4. The second signal is probably
obscured by the phenyl protons in the region, δ 7.26Ϫ7.67,
while no signal is found for compound 5, due to its poor
solubility, and low resolution in CDCl3. Methyl protons ap-
pears as a doublet in the range, ca. δ 1.92Ϫ1.98 in com-
pounds 1 and 2 and as a pair of doublets in the range, ca.
δ 2.00Ϫ2.19 in compounds 3Ϫ5. A quartet of signals is
observed for -CH protons in the region δ 7.60Ϫ7.88 in com-
pounds 1 and 2. PPh3 protons appear as a multiplet in the
region, δ 7.26Ϫ7.67.
Each of compounds 1Ϫ5 shows a single signal in its 31P
NMR spectrum and the coordination shifts range from ∆δ,
1.47Ϫ2.08 for complexes 1, 4 and 5. An higher coordination
shift of ∆δ 34.71 is observed for complex 3 and is similar
to that found in sulfur bridged dimers [12], indicating iso-
merisation of halogen bridging to sulfur bridging in the
solution phase. A negative coordination shift of ∆δ, Ϫ0.9
for complex 2 may be due to the equilibrium between the
coordinated PPh3 (δ Ϫ114.04) and free PPh3 (δ Ϫ113.15)
in the solution state.
Figure 8 Packing diagram of [CuBr(Hactsc)(PPh3)2] (4).
bonded to S atom of acetone thiosemicarbazone {CuϪS,
Conclusion
˚
˚
2.373(1) A}, bromine atom {CuϪBr, 2.475(1) A} and two
P atoms of two PPh3 {CuϪP, 2.267(1) and 2.279(1) A}
The presence of methyl substituents at C2 carbon of thiose-
micarbazones, Hactsc and Hmtsc, seems to play an import-
˚
(Figure 7). These CuϪP, CuϪS and CuϪBr bond distances
Z. Anorg. Allg. Chem. 2007, 1820Ϫ1826
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www.zaac.wiley-vch.de
1825

T. S. Lobana, S. Khanna, R. J. Butcher
ant role in stabilizing halogen bridging. For R1 ϭ R2 ϭ Ph;
R1 ϭ Py, R2 ϭ H, only monomers (X ϭ Cl, Br, I) are
formed [12, 15]. On the contrary, for R1 ϭ Ph, R2 ϭ H,
both monomers (X ϭ Br, I) and halogen bridged (X ϭ Br)
as well as sulfur bridged (X ϭ Cl) dimers [12] are formed,
while with R1 ϭ Me and R2 ϭ Ph, only halogen bridged
(X ϭ Cl, Br) dimers, and an unsymmetrically bridged dimer
(via iodine and sulfur) are favored and no monomer is ob-
served [16]. However, with R1 ϭ Me, R2 ϭ H, only halogen
bridged dimers (X ϭ Br 1, I 2) and with R1 ϭ R2 ϭ Me,
both monomer (X ϭ Br 4) and dimer (X ϭ I3) are formed.
[4] D. X. West, A. E. Liberta, S. B. Padhye, R. C. Chilate, P. B.
Sonaware, A. S. Kumbhar, R. G. Yerande, Coord. Chem. Rev.
1993, 123, 49.
[5] J. S. Casas, M. S. Garcia-Tasende, J. Sordo, Coord. Chem. Rev.
2000, 209, 197.
[6] M. Joseph, M. Kuriakose, M. R. P. Kurup, E. Suresh, A.
Kishore, S. G. Bhat, Polyhedron 2006, 25, 61.
[7] R. K. Mahajan, T. P. S. Walia, Sumanjit, T. S. Lobana, Anal.
Sci. 2006, 22, 389.
[8] A. M. Thomas, A. D. Naik, M. Nethaji, A. R. Chakravarty,
Inorg. Chim. Acta 2004, 357, 2315.
[9] J. S. Casas, E. Castellano, M. D. Couce, J. Ellena, A. Sanchez,
J. Sordo, C. Taboada, J. Inorg. Biochem. 2006, 100, 1858.
[10] R. K. Mahajan, I. Kaur, T. S. Lobana, Talanta 2003, 59, 101.
[11] S. Lhuachan, S. Siripaisarnpipat, N. Chaichat, Eur. J. Inorg.
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Supplementary material. Supplementary data is available from
CCDC, 12 Union Road,Cambridge CB2 1EZ, UK (fax:
ϩ44-12336033; e-mail: deposit@ccdc.cam.ac.uk) on request quot-
ing the deposition number CCDC643688 for 1, 643689 for 2,
643690 for 3 and 643691 for 4.
[14] J. Valdes-Martinez, A. Sierra-Romera, C. Alvarez-Toledano,
R. A. Toscano, H. Garcia-Tapia, J. Organomet. Chem. 1988,
352, 321.
Acknowledgements. Financial assistance from CSIR, New Delhi
(F.No.9/254(159)/2005-EMR-I) is gratefully acknowledged.
[15] T. S. Lobana, S. Khanna, R. J. Butcher, A. D. Hunter, M.
Zeller, Polyhedron 2006, 25, 2755.
[16] T. S. Lobana, S. Khanna, R. J. Butcher, A. D. Hunter, M.
Zeller, Inorg. Chem. doi: 10.1021/ic700401h, 2007.
[17] J. E. Huheey, E. A. Keiter, R. L. Keiter, Inorganic Chemistry:
Principals of Structure and Reactivity, 4th edit. Harper Collins
College, Publishers, New York, 1993.
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1826
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Z. Anorg. Allg. Chem. 2007, 1820Ϫ1826