Cyclopentanone thiosemicarbazone (Hcptsc) induces a new bonding pattern in (Ph3P)Cu(μ-Br)(μ3-S,N-Hcptsc)CuBr(PPh3) dimer

Article abstract of DOI:10.1016/j.inoche.2007.10.001

Reaction of cyclopentanone thiosemicarbazone (Hcptsc) with copper(I) bromide and Ph₃P in 1:1:1 molar ratio in acetonitrile has formed an asymmetric dimer, [(Ph₃P)Cu(μ-Br)(μ₃-S,N-Hcptsc)CuBr(PPh₃)] (1), with a new {Cu(μ-Br)(μ₃-S,N)Cu} bonding core in metal-thiosemicarbazone chemistry.

Full text of DOI:10.1016/j.inoche.2007.10.001

Available online at www.sciencedirect.com
Inorganic Chemistry Communications 11 (2008) 11–14
www.elsevier.com/locate/inoche
Cyclopentanone thiosemicarbazone (Hcptsc) induces a new
bonding pattern in (Ph3P)Cu(l-Br)(l3-S,N–Hcptsc)CuBr(PPh3) dimer
a,
a
b
Tarlok S. Lobana *, Poonam Kumari , Ray J. Butcher
a
Department of Chemistry, Guru Nanak Dev University, Amritsar 143 005, India
b
Department of Chemistry, Howard University, Washington, DC 20059, USA
Received 22 August 2007; accepted 2 October 2007
Available online 13 October 2007
Abstract
Reaction of cyclopentanone thiosemicarbazone (Hcptsc) with copper(I) bromide and Ph3P in 1:1:1 molar ratio in acetonitrile has
formed an asymmetric dimer, [(Ph3P)Cu(l-Br)(l3-S,N–Hcptsc)CuBr(PPh3)] (1), with a new {Cu(l-Br)(l3-S,N)Cu} bonding core in
metal-thiosemicarbazone chemistry.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Cyclopentanone thiosemicarbazone; Copper; Triphenyl phosphine; Asymmetric dimer; Bridging mode
The chemistry of thiosemicarbazones with copper(I) is
of current interest in view of their variable bonding modes,
structures as well as their biological [1–7] and analytical
applications [8]. In the literature, both halogen (Mode A)
and sulfur bridging (Mode B) have been observed in the
complexes of copper(I) halides (CuX) with thiosemicarba-
zones based on aldehydes (Structure I, R1 = Ph, pyrrole,
etc.; R2 = H, Chart 1) [3–5]. The exhibition of these bridg-
ing modes revealed that there is small energy difference
between these bridging modes (A, B), and the type of the
halogen as well as the substituents at C2 can determine
the type of a mode in the complex.
Mode C has been observed only in [Cu2(l-I)2(l-S-Hap-
tsc)(PPh3)2] in which two iodine and one S atoms are bridg-
ing two copper atoms [9].
In this communication, the behaviour of a thiosemicar-
bazone in which C2 carbon is a part of the ring (Structure
II, Chart 1) is reported. In a typical reaction, cyclopenta-
none thiosemicarbazone (Hcptsc) with copper(I) bromide
in the presence of PPh3 in CH3CN has yielded a compound
of stoichiometry, Cu2Br2(PPh3)2(Hcptsc). X-ray crystallog-
raphy has shown that it exists as a dimer, [(Ph3P)Cu(l-Br)-
(l3-S,N-Hcptsc)CuBr(PPh3)] (1), with a new {Cu(l-Br)(l3-
S,N)Cu} coordination core (Mode D).
Reaction of CuBr (0.025 g, 0.174 mmol) with cyclo-
pentanone thiosemicarbazone (0.027 g, 0.174 mmol) in
the presence of Ph3P (0.046 g, 0.174 mmol) in 20 mL aceto-
nitrile in 1:1:1 molar ratio has formed a compound of stoi-
chiometry Cu2Br2(PPh3)2(Hcptsc) (Scheme 1). Its IR
spectrum showed the presence of m(N–H) bands at 3468,
3268 cmÀ1 (due to –N1H2) and 3153 cmÀ1 (due to –N2H–
). Further, the most characteristic thioamide band due to
m(C@S) appeared at 847 cmÀ1 in the complex, which is at
low enegy region vis-a-vis the free ligand (866 cmÀ1). Thus
`
IR shows that Hcptsc is coordinating to the metal center
via S donor atom as a neutral ligand. A band due to
m(P–CPh) at 1097 cmÀ1 indicates the presence of Ph3P.
The crystal structure of Cu2Br2(PPh3)2(Hcptsc) has
shown that this compound exists as a dimer [(Ph3P)Cu-
(l-Br)(l3-S,N–Hcptsc)CuBr(PPh3)] (1), in which two cop-
per atoms are differently coordinated. One copper atom
is bonded to one terminal Br, one bridging Br, one P and
one bridging S atoms, while the second copper atom is
bonded to one bridging Br, one P, one N3 and one bridging
S atoms. The ligand Hcptsc adopts N3, S-chelation-cum-S
*
Corresponding author. Fax +91 183 2 258820.
E-mail address: tarlokslobana@yahoo.co.in (T.S. Lobana).
1387-7003/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2007.10.001

12
T.S. Lobana et al. / Inorganic Chemistry Communications 11 (2008) 11–14
X
S
R
R
NH
C
Cu
Cu
Cu
C
N
NH2
X
(A)
(I)
S
S
S
I
Cu
Cu
Cu
(B)
I
(C)
S
N3
S
C
NH
N
R
NH2
Cu
Cu
(II)
X
(D)
Chart 1.
H
S
N
Fig. 1. Structure of complex 1 with atomic numbering scheme. Selected
C
N
C
˚
NH2
bond lengths (A) and angles (°): Cu(1)–P(1) 2.217(8), Cu(2)–P(2) 2.210,
Cu(1)–S 2.426(9), Cu(2)–S 2.344(8), Cu(1)–Br(1) 2.450(5), Cu(1)–Br(2)
2.488(5), Cu(1)–Cu(2) 2.771(5), Cu(2)–N(3) 2.076(3), Cu(2)–Br(2)
2.488(5), and P(1)–Cu(1)–Br(1) 113.62(2), S–Cu(1)–Br(1) 96.23(2), P(1)–
Cu(1)–Br(2) 111.94(2), S–Cu(1)–Br(2) 109.23(2), N(3)–Cu(2)–P(2)
126.62(8), N(2)–Cu(2)–S 117.33(3), N(3)–Cu(2)–Br(2) 102.22(8), S–
Cu(2)–Br(2) 111.98(3), Cu(1)–Br(2)–Cu(2) 67.68(15), Cu(2)–S–Cu(1)
71.03(2), C(1)–S–Cu(2) 95.61(11).
6
CuBr,
Ph3P
PPh3
Br
Br
Ph3P
Cu
Cu
N3
H
C
S
C
angular adjustment for accommodation of unusual bridg-
ing pattern. The bond angles around each copper atom
{Cu(I), Cu(2)} indicate distorted tetrahedral geometry.
The angles at bridged sulfur and bridged bromine atoms
{Cu–S–Cu}, 71.03(2)°; Cu–Br–Cu, 67.68(15)° are much
shorter relative to the angles observed in bridged sulfur
and bromine dimers {Cu–S–Cu}, 77.80(2)° and Cu–Br–
Cu, 74.22(2)° [3]. From the packing diagram of 1, it can
be seen that the hydrogen atoms of amino group are
engaged in both the inter- and intra-molecular hydrogen
bonding. One hydrogen atom of the amino group forms
an intermolecular hydrogen bond {H–N1–HÁ Á ÁBr(1),
N
H2N
1
Scheme 1.
bridging in complex 1. The unequal Cu–S {2.344(8),
2.426(9) A} and equal Cu–Br {2.488(5) A each} distances
reveal that Cu2SBr core is slightly distorted square planar.
˚
˚
˚
˚
As expected, the bridging Cu–S distance {2.426(9) A} is
longer than the terminal Cu–S distance {2.344(2) A} in
bromo bridged dimer, [Cu2(l-Br)2(g1-S-Hbtsc)2(Ph3P)2]
˚
2.53 A} with the terminal bromine atom, while the second
hydrogen atom of the amino group forms intramolecular
hydrogen bond with the bridging Br atom {H–N1–
(2) (Structure I, R = Ph, Hbtsc) [3], while the bridging
˚
Cu–S distance {2.344(8) A} is same as in 2. The bridging
˚
˚
HÁ Á ÁBr(2), 2.86 A}. Thus in this complex, various dimeric
Cu–Br distance is comparable with that {2.485(8) A} in 2
˚
units are linked together by intermolecular hydrogen bond-
ing and form a polymeric chain (see Fig. 2).
[3] and terminal Cu–Br distance {2.450(5) A} is shorter
than {2.548(8) A} in [CuBr(g1-S-Hpytsc)(Ph3P)2] (3)
˚
In 1H NMR spectrum of 1, the most characteristic N2H
signal at d 10.15 ppm is shifted to low field compared with
the free ligand (d 8.42 ppm) [12]. The signals due to N1H2
protons at d 7.18, 6.41 ppm in the free ligand are obscured
by PPh3 in 1. Ring protons appear at d 2.16 (C3,6H2) and
1.60 ppm (C4,5H2), which are upfield relative to the free
ligand (d 2.40, 1.78 ppm, respectively). In 13C NMR, ring
carbons C3, C4, C5 and C6 appear at d 38.1, 25.4, 29.4
and 31.2 ppm, respectively, which are downfield compared
with the free ligand {d 33.2–27.7 ppm} [12]. The signals due
(Structure I, R = pyridine, Hpytsc) [3]. Also Cu(2)–N(3)
distance {2.076(3) A} is normal, and similar to the litera-
ture trends [10]. The terminal Cu–P distances {2.217(8),
˚
˚
˚
2.210(8) A} are close to {2.234(13) A} in 2 [3]. The
˚
CuÁ Á ÁCu separation in 1 {2.771(5) A} is less than twice
˚
the van der Waals radius of the Cu atom {2.80 A} [11]
(see Fig. 1).
The bond angles around Cu(I), Cu(2), S and Br atoms
{109.23(2)°, 111.98(3)°, 71.03(2)° and 67.68(15)°, respec-
tively} in central Cu(l-Br)(l-S,N)Cu core, reveal severe

T.S. Lobana et al. / Inorganic Chemistry Communications 11 (2008) 11–14
13
˚
c = 14.2451(14) A, a = 76.175(2)°, b = 72.646(2)°, c =
3
˚
64.567(2)°, V = 961.52(16) A , T = 293(2) K, space group
calcd = 1.671 mg mÀ3
,
Z = 1,
l(Mo
Ka) =
ꢀ
P1,
q
3.357 mmÀ1, 7553 reflections measured on a Bruker
SMART CCD-1000 diffractometer, unique 6176 (Rint
=
0.0254). The final R1 0.0331 was for 5872 reflections
[I > 2.0r(I)] and wR2 was 0.0869.
Acknowledgement
Financial support from CSIR {Scheme no. 01(1993)/05/
EMR II}, New Delhi is gratefully acknowledged.
Appendix A. Supplementary material
CCDC 657238 contains the supplementary crystallo-
graphic data for 1. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online
version, at doi:10.1016/j.inoche.2007.10.001.
Fig. 2. Packing diagram of complex 1.
References
to the carbon atoms of the PPh3 are clearly resolved and
appear at d 133.9 (o-C), 132.2 (i-C), 129.8 (p-C) and
128.5 ppm (m-C). Other signals due to C1 and C2 carbons
could not be detected. The 31P NMR spectrum shows a sin-
gle broad signal at d À114.34 ppm with the upfield coordi-
nation shift {Dd} of À1.19 ppm in 1.
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It is concluded from above that in the literature, com-
plexes of cyclopentanone thiosemicarbazone (Hcptsc) with
C2 carbon being part of the ring have exhibited g1-S bonding
in [CuI(Hcptsc)(Ph3P)2] [13], N3, S-chelation mode in
[Hg(cptsc)Ph] [12] and [Tl(cptsc)Ph2] [14]. Surprisingly, in
complex 1, it has shown a new coordination core, Cu(l-
Br)(l-S-Hcptsc)Cu, (mode D), not reported to date in
metal-thiosemicarbazone chemistry. Also, complex 1 repre-
sents the first dimer formed by a ligand such as Hcptsc, in
which C2 is part of the ring. Another similar ligand, namely,
isatin-3-thiosemicarbazone has formed only tetrahedral [15]
and octahedral [16] mononuclear complexes.
Compound 1: M.p. 220–224 °C (melt), yield, 0.042 g, 50%.
C, H, N, analysis for Cu2Br2H42C40N3P2S: C, 52.08; H, 4.13;
N, 4.34. Found: C, 52.24; H, 4.10; N, 4.29%. Main IR peaks
(KBr, cmÀ1): m(N–H), 3468s, 3268s (–NH2), 3153m (–NH);
d(NH2) + m(C@N) + m(C–C), 1604s, 1546s; m(C@S) + m(C–
N), 1068s, 1027s, 847m (thioamide moiety); m(P–CPh),
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(2005) 755;
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A 45 (2006) 639.
1
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(1997) 4289.
7.21–7.51(m, Ph), 2.16 (s, C3,6H2), 1.60 (s, C4,5H2). 13C
NMR data (d, ppm; CDCl3), 25.4 (C4), 29.5 (C5), 31.2
(C6), 38.1 (C3), 128.5 (m-C, JP–C = 11.4 Hz), 129.8 (p-C),
132.4 (i-C, JP–C = 41.6 Hz), 133.9 (o-C, JP–C = 36.1 Hz).
31P NMR data (d, ppm; CDCl3), À114.34 ppm, Dd
(dcomplex À dligand) = À1.19 ppm.
Crystallographic data for 1: C42H40Br2Cu2N3P2S,
˚
˚
M = 967.67, triclinic, a = 8.6797(8) A, b = 9.0973(9) A,

14
T.S. Lobana et al. / Inorganic Chemistry Communications 11 (2008) 11–14
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