Pyridine-2-thione (pySH) derivatives of silver(I): Synthesis and crystal structures of dinuclear [Ag2Cl2(μ-S-pySH)2(PPh3)2] and [Ag2Br2(μ-S-pySH)2(PPh3)2] complexes

Article abstract of DOI:10.1016/j.poly.2008.01.008

Reaction of silver(I) halides with PPh₃ in acetonitrile and then with pyridine-2-thione (pySH) chloroform (1:1:1 molar ratio) has yielded sulfur bridged dimers of general formula, [Ag₂X₂(μ-S-pySH)₂(PPh₃)₂] (X = Cl, 1, Br, 2). Both these complexes have been characterized using analytical data, NMR spectroscopy and single crystal X-crystallography. The central Ag₂S₂ cores form parallelograms with unequal Ag-S bond distances (2.5832(8), 2.7208(11) A?) in 1 and (2.6306(4), 2.6950(7) A?) in 2, respectively. The Ag?Ag contacts of compounds 1 and 2 are 3.8425(8) and 3.8211(4) A?, respectively. The angles around Ag (in the range 87.19(2)-121.71(2)° in 1 and 87.81(2)-121.53(2)° in 2) reveal highly distorted tetrahedral geometry. There are inter dimer π-π stacking interactions between pyridyl rings (inter ring distances of 3.498 and 3.510 A? in complexes 1 and 2, respectively). The solution state ³¹P NMR spectroscopy has shown the existence of both monomers and dimers. The studies reveal relatively weaker intramolecular -NH?Cl hydrogen bonding in case of AgCl vis-a?-vis that in CuCl which favored both a monomer and a dimer with AgCl, and only a monomer with CuCl.

Full text of DOI:10.1016/j.poly.2008.01.008

Available online at www.sciencedirect.com
Polyhedron 27 (2008) 1375–1380
www.elsevier.com/locate/poly
Pyridine-2-thione (pySH) derivatives of silver(I): Synthesis and
crystal structures of dinuclear [Ag2Cl2(l-S-pySH)2(PPh3)2]
and [Ag2Br2(l-S-pySH)2(PPh3)2] complexes
a,
a
b
*
Tarlok S. Lobana , Rohit Sharma , 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 11 September 2007; accepted 4 January 2008
Available online 21 February 2008
Abstract
Reaction of silver(I) halides with PPh3 in acetonitrile and then with pyridine-2-thione (pySH) chloroform (1:1:1 molar ratio) has
yielded sulfur bridged dimers of general formula, [Ag2X2(l-S-pySH)2(PPh3)2] (X = Cl, 1, Br, 2). Both these complexes have been char-
acterized using analytical data, NMR spectroscopy and single crystal X-crystallography. The central Ag2S2 cores form parallelograms
˚
˚
with unequal Ag–S bond distances (2.5832(8), 2.7208(11) A) in 1 and (2.6306(4), 2.6950(7) A) in 2, respectively. The Agꢀ ꢀ ꢀAg contacts of
˚
compounds 1 and 2 are 3.8425(8) and 3.8211(4) A, respectively. The angles around Ag (in the range 87.19(2)–121.71(2)° in 1 and
87.81(2)–121.53(2)° in 2) reveal highly distorted tetrahedral geometry. There are inter dimer p–p stacking interactions between pyridyl
rings (inter ring distances of 3.498 and 3.510 A in complexes 1 and 2, respectively). The solution state 31P NMR spectroscopy has shown
˚
the existence of both monomers and dimers. The studies reveal relatively weaker intramolecular –NHꢀ ꢀ ꢀCl hydrogen bonding in case of
`
AgCl vis-a-vis that in CuCl which favored both a monomer and a dimer with AgCl, and only a monomer with CuCl.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Silver(I); Pyridine-2-thione; Triphenyl phosphine; Crystal structure
1. Introduction
plexes, [AgL2(SCN)] (L = 1, 3-imidazolidine-2-thione) [9e]
and [Ag(pymSH)(PPh3)2](NO3) (pymSH = pyrimidine-2-
thione) [9b] and in a linear complex, [AgL2](ClO4)
(L = 1, 3-imidazolidine-2-thione) [9f]; while mode IIB was
shown in dimers, [Ag2Br2(pymSH)2(PPh3)2] [10a], [Ag2(l-
Pyridine-2-thione (I, pySH) bearing the functional
group, –N(H)–C(@S)– M –N@C(–SH)–, is the simplest
prototype of heterocyclic thioamides and it has shown
diverse bonding properties both in neutral and in anion
forms (after losing –NH hydrogen) and has formed mono-
mers, dimers, oligomers and polymers [1–8]. Among the
coinage metals, neutral pyridine-2-thiones have shown
modes IIA–IIC with copper(I) halides [1–8]. As regards sil-
ver(I), mode IIA has been shown by py2SH/allied hetero-
cyclic thioamides in distorted tetrahedral complexes,
[Ag(py2SH)(PPh3)2Cl] [9a], [Ag(pySH)2(PPh3)2](NO3)
[9b], [Ag(pySH-1-Me)4](BF4) [9c], [AgL2(PPh3)2](NO3)
(L = benzoxazoline-2-thione) [9d], in trigonal planar com-
S-pySH)2(l-P,P-dppb)2](NO3)2
(dppb = Ph2P–(CH2)4-
PPh2) [10b], in polymers {Ag(pySH)Cl}n [10c] and
[{Ag(pySH)2}(ClO4)(H2O)0.5]n [9f]; Mode IID with a l4–S
mode of bonding of neutral pySH has been shown in
{Ag4(pySH)6(NO3)4}n polymer [11].
5
4
3
6
HN
M
HN
M
HN
M
HN
M
HN
1
2
S
S
S
S
S
M
M
M
M
M
M
*
I
II A
II B
II C
Corresponding author. Tel.: +91 183 22 57604; fax: +91 183 2258820.
II D
E-mail address: tarlokslobana@yahoo.co.in (T.S. Lobana).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.01.008

1376
T.S. Lobana et al. / Polyhedron 27 (2008) 1375–1380
and stirring was carried out for 24 h. Acetonitrile was
removed from the white colored precipitates and chloro-
form (15 mL) was added. To the precipitates suspended
in CHCl3 solid pyridine-2-thione (0.019 g, 0.17 mmol)
was added and the contents were stirred for 1 h until a clear
solution was obtained. Slow evaporation of solution at
room temperature formed a solid mass which was treated
with diethyl ether to remove any unreacted PPh3 and then
crystallized from methanol–dichloromethane mixture
(25:75:v/v). The yellow colored crystals were formed.
Yield: 65%; m.p. 190–195 °C. Anal. Calc. for AgBrC23-
H20NSP: C, 49.22; H, 3.55; N, 2.49. Found: C, 49.50; H,
3.91; N, 2.49%. Main IR peaks (KBr, cmꢁ1); m(N–H),
3170(m); t(C–H) 3058(m)–3035(m); m(C@N) + t(C@C);
While several dimeric complexes of copper(I) halides
with heterocyclic thioamides are reported [12], there are
only two dimeric complexes of heterocyclic thioamides
with silver(I), namely, [Ag2Br2(pymSH)2(PPh3)2] (pymSH
= pyrimidine-2-thione) [10a] and [Ag2(l-S-pySH)2-(l-P,P-
dppb)2](NO3)2 (dppb = Ph2P-(CH2)4-PPh2) [10b]. In this
paper, dimeric complexes of silver(I) halides with pyri-
dine-2-thione are reported and characterized using analyt-
ical data, NMR spectroscopy and single crystal X-ray
crystallography.
2. Experimental
2.1. Materials and techniques
1608(m)–1569(s);
d(N–H) + d(C–H)
1498(s)–1361(s);
m(C@N), 1608(w); m(C@S), 1128(s); m(P–CPh), 1093(m).
1H NMR data (d, CDCl3): 7.78 (d, H6); 7.67 (m, H4);
7.57(d, H3); 6.91(t, H5); 7.32–7.53 (PPh3). 31P NMR
Pyridine-2-thione and triphenyl phosphine were pro-
cured from Aldrich–Sigma Ltd. Silver(I) halides were
freshly prepared from AgNO3 and NaBr, or KCl and dried
in vacuo. Elemental analysis for C, H and N were carried
out using a thermoelectron FLASHEA1112 analyser. The
melting points were determined with a Gallenkamp electri-
cally heated apparatus. The IR spectra of the ligands and
the complexes were recorded on the FTIR-SHIMADZU
8400 Fourier Transform spectrophotometer in the range,
(CDCl3), d = ꢁ 100.6, Ddðdcomplex ꢁ dPPh Þ ¼ 12:6 ppm. dP,
3
ꢁ78.29, Dd = 34.86 ppm.
2.4. Crystallography
Single crystals of compounds 1 and 2 were mounted on
1
4000–500 cmꢁ1 (using KBr pellets). H NMR spectra were
CCD area detector diffractometer, equipped with a graph-
˚
ite monochromator and Mo Ka radiator (k = 0.71073 A).
recorded on a JEOL AL300 FT spectrometer at 300 MHz
in CDCl3 with TMS as the internal reference. The 31P
NMR spectra were recorded at 121.5 MHz with (CH3O)3P
as the external reference taken as zero position.
The unit cell dimensions and intensity data were measured
at 93(2) K. The structures were solved by the direct meth-
ods, and refined by the full matrix least square based on
F2 with anisotropic thermal parameters for the non-hydro-
gen atoms using Bruker SMART (data collection and cell
refinement), Bruker SAINT (data reduction) SHELXS-97
(structure solution), and SHELXL-97 (structure refinement)
and Bruker SHELXTL (molecular graphics) [13–16]. A
multi-scan absorption correction (SADABS) was applied.
2.2. Synthesis of [Ag2(l-S-pySH)2(PPh3)2Cl2] (1)
To AgCl (0.025 g, 0.17 mmol) suspended in 20 mL of ace-
tonitrile was added solid PPh3 (0.045 g, 0.17 mmol) and stir-
ring was carried out for 24 h. Acetonitrile was removed from
the white colored precipitates and chloroform (15 mL) was
added. To these precipitates suspended in chloroform, solid
pyridine-2-thione (0.019 g, 0.17 mmol) was added, and the
contents stirred for 1 h until clear solution was obtained.
Slow evaporation of the solution at room temperature
formed a solid mass which was crystallized from metha-
nol–dichloromethane mixture (20 mL, 1:3 v/v). The yellow
colored crystals were formed. Yield: 60%; m.p. 155–57 °C.
Anal. Calc. for AgClC23H20NSP: C, 53.43; H, 3.87; N,
2.71. Found: C, 53.78; H, 3.70; N, 3.01%. Main IR peaks
(KBr, cmꢁ1), t(N–H), 3178(m); t(C–H), 3035–2920(m);
t(C@N) + t(C–C); 1608(m)–1571(s); d(N–H) + d(C–H),
1500(s)–1363(s); t(C@S), 1130(s); t(P–CPh) 1093(m). 1H
NMR (d, CDCl3), d = 7.81(d, H6), 7.26–7.63m (Ph3P +
C3,4H); 6.89(t, H5). 31P NMR (CDCl3), d = ꢁ98.4 ppm,
3. Results and discussion
3.1. Synthesis and IR spectroscopy
Reaction of silver(I) chloride with PPh3 in acetonitirile
and then with pyridine-2-thione chloroform (1:1:1 molar
ratio) yielded compound of stoichiometry, {AgCl
(pySH)(PPh3)} and similar reaction with silver(I) bromide
yielded, {AgBr(pySH)(PPh3)}. The X-ray crystallography
has shown both compounds to be dimers, [Ag2Cl2(l-S-
pySH)2(PPh3)2]
(Scheme 1).
1 and [Ag2Br2(l-S-pySH)2(PPh3)2] 2
Complexes showed m(N–H) peaks at 3178 cmꢁ1 in 1 and
at 3170 cmꢁ1 in 2, and it revealed that there is no deproto-
nation of NH proton of pySH ligand. The diagnostic
Ddðdcomplex ꢁdPPh Þ ¼ 14:8 ppm. dP, –78.63, Dd = 34.80 ppm.
3
CH3CN
[Ag2X2(μ−S-pySH)2(PPh3)2]
X = Cl 1, Br 2
2AgX + 2PPh3
+
2
2.3. Synthesis of [Ag2(l-S-pySH)2(PPh3)2Br2] (2)
CHCl3
S
N
H
To AgBr (0.025 g, 0.13 mmol) suspended in 20 mL of
acetonitrile was added solid PPh3 (0.070 g, 0.26 mmol)
Scheme 1.

T.S. Lobana et al. / Polyhedron 27 (2008) 1375–1380
1377
m(C@S) peak in free pySH ligand occurs at 1138 cmꢁ1 [12],
which is shifted to lower energy region in complexes, at
1130 cmꢁ1 1 and 1128 cmꢁ1 2. These trends in m(C@S)
and m(N–H) peaks suggest coordination by thione sulfur
donor atom. The m(C–H) peaks fall in the regions 3055–
2920 cmꢁ1; while other peaks due to m(C–C) + m(C@N) +
d(N–H) + d(C–H) fall in the region, 1332–1608 cmꢁ1. A
characteristic peak due to m(P–CPh) at 1093 cmꢁ1 indicated
the presence of PPh3 in the complexes.
In complex 1, Ag is bonded to one Cl atom, one P atom
of Ph3P and one S atom of pySH forming three coordinate
unit, {AgCl(Ph3P)(pySH)}, and two such units dimerize via
the bonded S atoms to yield sulfur-bridged dimer
[Ag2Cl2(l-S-pySH)2(PPh3)2] (1) (Fig. 1). The formation of
[Ag2Br2(l-S-pySH)2(PPh3)2] (2) (Fig. 2) is similar with Br
as the anion. The central Ag2S2 core forms a parallelogram
with two unequal Ag–S bond distances (2.5832(8),
˚
˚
2.7208(11) A) in 1 and (2.6306(4), 2.6950(7) A) in 2, respec-
tively. These bridging Ag–S bond distances are in the range
˚
3.2. Crystal structures of the complexes
of terminal Ag–S bond distance, 2.625 A in [AgCl-
(pySH)(PPh3)2] [9a]. The S–Ag–S and Ag–S–Ag bond
angles within the {Ag(l-S)2Ag} core of 1 are 87.190(15)°
and, 92.810(15)° 1, respectively. The similar angles are
87.814(18)° and 92.187(18)° in 2. The angles around Ag
vary in the range 87.19(2)–121.71(2)° in 1, and 87.81(2)–
121.53(2)° in 2, which indicate highly distorted tetrahedral
geometries. Finally the Ag–S–C bond angles are 105.10(6)°,
Compounds [Ag2(l-S-pySH)2Cl2(PPh3)2] 1 and [Ag2(l-
S-pySH)2Br2(PPh3)2] 2 crystallized as triclinic crystals in
space group P1. The atomic numbering schemes of com-
plexes 1 and 2 are shown in Figs. 1 and 2, respectively.
Crystal data are given in Table 1 and bond lengths and
angles are given in Table 2.
ꢀ
Fig. 1. Structure of complex 1 showing the atomic numbering scheme.
Fig. 2. Structure of complex 2 showing the atomic numbering scheme.

1378
T.S. Lobana et al. / Polyhedron 27 (2008) 1375–1380
Table 1
Crystal data and refinement details for complexes 1 and 2
1
2
Empirical formula
M
C46H40Ag2Cl2N2P2S2
1033.50
C46H40Ag2Br2N2P2S2
1122.42
T (K)
93(2)
93(2)
Crystal system
Space group
Unit cell dimensions
triclinic
triclinic
ꢀ
ꢀ
P1
P1
˚
a (A)
9.520(3)
9.526(1)
˚
b (A)
9.507(3)
9.583(1)
˚
c (A)
14.014(5)
14.121(2)
a (°)
b (°)
c (°)
71.563(5)
77.357(6)
62.924(5)
1067.1(6)
77.512(2)
72.176(2)
63.011(2)°
1088.9(3)
3
˚
V (A )
Z
1
1
Dcalc (mg mꢁ3
)
1.608
1.251
1.712
2.938
l (mmꢁ1
)
Reflections collected
8376
8192
Unique reflections [R(int)]
Reflections with [I > 2r(I)]
Final R indices [I > 2r(I)]
R indices (all data)
5003 [0.0268]
4807
R1 = 0.0254, wR2 = 0.0665
R1 = 0.0267, wR2 = 0.0673
5049 [0.0161]
4438
R1 = 0.0235, wR2 = 0.0562
R1 = 0.0306, wR2 = 0.0600
Table 2
are higher than twice the sum of van der Waals radius of
Ag atom, 3.40 A.
˚
˚
Selected bond length (A) and angles(°) for 1 and 2
1
There are inter dimer p–p stacking interactions between
Ag–P
Ag–Cl
S–C(1)
P–Ag–Cl
Cl–Ag–S
Cl–Ag–S#1
Ag–S–C(1)
Ag#1–S–C(1)
2.435(1)
2.530(1)
1.722(2)
121.71(2)
103.91(2)
112.24(3)
109.93(6)
105.10(6)
Ag–S
Ag–S
2.721(1)
2.583(1)#1
3.8425(8)
101.35(2)
120.70(2)
92.81(2)
87.19(2)
pyridyl rings. The inter ring distances are 3.498 and
˚
3.510 A in complexes 1 and 2, respectively. Packing dia-
Agꢀ ꢀ ꢀAg
P–Ag–S
P–Ag–S#1
Ag–S–Ag
S–Ag–S
grams are shown in Figs. 3 and 4.
3.3. NMR spectroscopy
Proton NMR spectra of sparingly soluble complexes,
[AgCl(pySH)(PPh3)]2 1 and [AgBr(pySH)(PPh3)]2 2, in
CDCl3 has been recorded. Complexes 1 and 2 show peaks
due to H6 proton at low field, d 7.81 and 7.78 ppm, respec-
2
Ag–P
Ag–S
S–C(1)
P–Ag–Br
S–Ag–Br
Br–Ag–S#1
Ag–S–C(1)
Ag#1–S–C(1)
2.441(1)
2.608(1)
1.717(2)
121.53(2)
109.47(2)
106.98(1)
103.79(8)
111.62(1)
Ag–Br
Ag–S#1
2.631(1)
2.695(1)
3.8211(4)
121.16(2)
102.44(2)
92.19(2)
87.81(2)
Agꢀ ꢀ ꢀAg
P–Ag–S
P–Ag–S#1
Ag–S–Ag
S–Ag–S#1
`
tively, vis-a-vis the free ligand (pySH) at d 7.56 ppm [12].
Likewise, H5 proton signals at d 6.89 (1) and 6.91 (2)
ppm are downfield (free pySH, d 6.73 ppm). The H3 and
H4 proton signals for 1 merged with the PPh3 signals in
the region, d 7.26–7.63 ppm; while in complex 2, these sig-
nals were clearly visible (see Section 2). The 31P NMR spec-
tra showed two peaks for each complex with coordination
shifts, 14.8, 34.80 ppm (1) and 12.6, 34.86 (2) ppm. These
data reveal that dimers (d 34.80, 34.86 ppm 1 and 2) prob-
ably set an equilibrium with monomers (14.8, 12.6 ppm,1a,
2a, respectively) in solution. The monomers are suggested
as AgX(pySH)(PPh3)2 (X = Cl, 1a; Br, 2a) formed by rear-
rangement of dimers in solution, a phenomenon observed
in copper(I) halide-thiosemicarbazone chemistry [18].
109.93(6)° in 1 and 103.79(8)°, 111.62(1)° in 2 and are sim-
ilar to that reported for [Ag(pySH)(PPh3)2Cl] [9a].
The Ag–Cl bond is strong as the bond distance in com-
˚
plex 1, 2.530(1) A is less than the sum of the ionic radii of
Ag+ and Cl , 2.7501 A [17]. The Ag–Br bond distance in
ꢁ
˚
˚
complex 2, 2.631(1) A, is shorter than the Ag–Br bridging
bond distance [2.7350(6), 2.8241(5) A] observed in
˚
[Ag2Br2(l-S-pymSH)2(PPh3)2] [10a]. The S–C bond dis-
˚
˚
tance 1.722(2) A in 1 is slightly larger than 1.717(2) A in
complex 2. This is due to high electronegativity of Clꢁ ver-
sus Brꢁ which weakens C–S bond in the former. The Ag–P
3.4. Electronic absorption spectroscopy
The electronic absorption spectrum of complex 1 in
dichloromethane showed three peaks at kmax values of
238, 270 and 359 nm. Similarly complex 2 has shown two
peaks at kmax values of 239, 271 and 359 nm. The peaks
˚
˚
bond distances are, 2.4346(10) A in 1 and 2.4414(6) A in 2,
which are nearly same. The Agꢀ ꢀ ꢀAg contacts of com-
˚
pounds 1 and 2 of 3.8425(8) and 3.8211(4) A, respectively,

T.S. Lobana et al. / Polyhedron 27 (2008) 1375–1380
1379
Fig. 3. Packing diagram of complex 1.
Fig. 4. Packing diagram of complex 2.
at 359 nm are attributed to –C@S groups due to n ? p*
transitions while other beaks are due to p ? p* transitions
based on pyridyl and phenyl rings. Neither of the two com-
pounds exhibited any fluorescence properties.
1; while for copper(I) chloride only monomer, [CuCl(pySH)-
(PPh3)2] is known to date as all efforts to get a dimer [Cu2Cl2
(l-S-pySH)2(PPh3)2] ended in the formation of only mono-
mer [CuCl(pySH)(PPh3)2] due to strong intramolecular –
NHꢀ ꢀ ꢀCl hydrogen bonding in the latter [12].
3.5. Conclusion
Acknowledgements
Pyridine-2-thione has formed hitherto unknown dimers
1 and 2. It may be noted that AgCl has formed both
previously known monomer, [Ag(pySH)(PPh3)2Cl] [9a],
and the newly formed dimer [Ag2Cl2(l-S-pySH)2(PPh3)2]
One of us (Rohit) thanks Guru Nanak Dev University
for research facilities. The authors also thank Razia Sul-
tana and Sonia Khanna for their help.

1380
T.S. Lobana et al. / Polyhedron 27 (2008) 1375–1380
(c) G. Giusti, G. Geier, A. Currao, R. Nesper, Acta Crystallogr., Sect.
Appendix A. Supplementary data
C 52 (1996) 1914;
(d) W. McFarlane, P.D. Akrivos, P. Aslanidis, P. Karagiannidis, C.
Hatzisymeon, M. Numan, S. Kokkou, Inorg. Chim. Acta 281 (1998)
121;
(e) M.B. Ferrari, C.G. Fava, M.E.V. Tani, Cryst. Struct. Commun.
10 (1981) 571;
CCDC 657505 and 657504 contain the supplementary
crystallographic data for 1 and 2. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033, or e-mail: depos-
it@ccdc.cam.ac.uk. Supplementary data associated with
this article can be found, in the online version, at
doi:10.1016/j.poly.2008.01.008.
(f) J. Sola, A. Lopez, R.A. Coxall, W. Clegg, Eur. J. Inorg. Chem.
(2004) 4871.
[10] (a) P.J. Cox, P. Aslanidis, P. Karagiannidis, S. Hadjikakou, Inorg.
Chim. Acta 310 (2000) 268;
(b) P. Aslanidis, P.J. Cox, S. Divanidis, P. Karagiannidis, Inorg.
Chim. Acta 357 (2004) 2677;
(c) M.Hong,W.Su,R.Cao,W.Zhang,J.Lu,Inorg.Chem.38(1999)600.
[11] W. Su, M. Hong, J. Weng, Y. Liang, Y. Zhao, R. Cao, Z. Zhou,
A.S.C. Chan, Inorg. Chim. Acta 331 (2002) 8.
References
[12] T.S. Lobana, A. Castineiras, Polyhedron 21 (2002) 1603.
[13] Bruker, SMART, SAINT and XPREP. Area Detector Control and Data
Integration and Reduction Software. Bruker Analytical X-ray
Instruments Inc., Madison, WI, USA, 1995.
[14] G.M. Sheldrick, SADABS, Program for Empirical Absorption Correc-
tion of Area Detector data, University of Gottingen, Gottingen,
Germany, 1997.
[15] G.M. Sheldrick, Acta Crystallogr., Sect. A 46 (1990) 467.
[16] G.M. Sheldrick, SHELXL-97, Program for the Refinement of Crystal
Structures, University of Gottingen, Gottingen, Germany, 1997.
[17] J.E. Huheey, E.A. Keiter, R.L. Keiter, Inorganic Chemistry: Princi-
ples of Structure and Reactivity, 4th ed., Harper Collins College
Publishers, New York, 1993.
[1] E.S. Raper, Coord. Chem. Rev. 61 (1985) 115.
[2] E.S. Raper, Coord. Chem. Rev. 153 (1996) 199.
[3] E.S. Raper, Coord. Chem. Rev. 129 (1994) 91.
[4] E.S. Raper, Coord. Chem. Rev. 165 (1997) 475.
[5] P.D. Akrivos, Coord. Chem. Rev. 213 (2001) 181.
[6] J.A. Garcia-Vazquez, J. Romero, A. Sousa, Coord. Chem. Rev. 193
(1999) 691.
[7] T.S. Lobana, Ritu Sharma, Renu Sharma, Sheetal Mehra, A.
Castineiras, Peter Turner, Inorg. Chem. 44 (2005) 1914.
[8] T.S. Lobana, Renu Sharma, Geeta Hundal, R.J. Butcher, Inorg.
Chem. 45 (2006) 9402.
[9] (a) P. Karagiannidis, P. Aslanidis, S.C. Kokkou, C.J. Cheer, Inorg.
Chim. Acta 172 (1990) 247;
[18] T.S. Lobana, Rekha, R.J. Butcher, A. Castineiras, E. Bermejo, P.V.
Bharatam, Inorg. Chem. 45 (2005) 1535.
(b) P. Aslanidis, P. Karagiannidis, P.D. Akrivos, B. Krebs, M. Lage,
Inorg. Chim. Acta 254 (1997) 277;