The influence of substituents at the C2 carbon of thiosemicarbazones on bonding and nuclearity of silver(I) complexes

Article abstract of DOI:10.1016/j.poly.2008.04.027

Several thiosemicarbazones of the type (R¹R²C²{double bond, long}N³-N²H-C({double bond, long}S)N¹H₂) were reacted with silver salts, yielding a variety of complexes with different ligand coordination modes, nuclearities and stoichiometries. Reaction of silver(I) chloride with 2-benzoylpyridine thiosemicarbazone, HL¹, has formed a sulfur-bridged dimer, [Ag₂Cl₂(μ-S-HL¹)₂(PPh₃)₂] 2, while a similar reaction with 2-acetylpyridine thiosemicarbazone, HL², has formed a mononuclear complex {AgCl(η¹-S-HL²)₂(PPh₃)] 1, with an unusual Ag:ligand:PPh₃ stoichiometry of 1:2:1. Reaction of silver(I) nitrate/acetate with benzophenone thiosemicarbazone, HL³, and acetone thiosemicarbazone, HL⁴, have yielded mononuclear complexes, [Ag(ONO₂)(η¹-S-HL³)(PPh₃)₂] 3, and [Ag(N³,S-HL⁴)(PPh₃)₂]X (X{double bond, long}NO₃ 4, CH₃COO 5). In complexes 1 and 3 and in dimeric complex 2, the ligands exhibit the usual η¹-S-bonding and μ-S-bridging coordination commonly observed for thiosemicarbazone ligands with tetrahedral coinage metal ions. In complexes 4 and 5, however, weak binding properties of nitrate or acetate anions to silver favored N³,S-chelation with the methyl substituents at the C² carbon of the thiosemicarbazones.

Full text of DOI:10.1016/j.poly.2008.04.027

Polyhedron 27 (2008) 2251–2258
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The influence of substituents at the C2 carbon of thiosemicarbazones on
bonding and nuclearity of silver(I) complexes
a
a
b
b
Tarlok S. Lobana a, , Sonia Khanna , Geeta Hundal , Ben-Jie Liaw , Chen W. Liu
*
a Department of Chemistry, Guru Nanak Dev University, Amritsar 143 005, India
b Department of Chemistry, National Dong Hwa University, Hualien 974, Taiwan
a r t i c l e i n f o
a b s t r a c t
Several thiosemicarbazones of the type (R1R2C2@N3–N2H–C(@S)N1H2) were reacted with silver salts,
yielding a variety of complexes with different ligand coordination modes, nuclearities and stoichiome-
tries. Reaction of silver(I) chloride with 2-benzoylpyridine thiosemicarbazone, HL1, has formed a
sulfur-bridged dimer, [Ag2Cl2(l-S–HL1)2(PPh3)2] 2, while a similar reaction with 2-acetylpyridine thio-
semicarbazone, HL2, has formed a mononuclear complex {AgCl(g1-S–HL2)2(PPh3)] 1, with an unusual
Ag:ligand:PPh3 stoichiometry of 1:2:1. Reaction of silver(I) nitrate/acetate with benzophenone
thiosemicarbazone, HL3, and acetone thiosemicarbazone, HL4, have yielded mononuclear complexes,
[Ag(ONO2)(g1-S–HL3)(PPh3)2] 3, and [Ag(N3,S–HL4)(PPh3)2]X (X@NO3 4, CH3COO 5). In complexes 1 and
3 and in dimeric complex 2, the ligands exhibit the usual g1-S-bonding and l-S-bridging coordination
commonly observed for thiosemicarbazone ligands with tetrahedral coinage metal ions. In complexes
4 and 5, however, weak binding properties of nitrate or acetate anions to silver favored N3,S-chelation
with the methyl substituents at the C2 carbon of the thiosemicarbazones.
Article history:
Received 25 January 2008
Accepted 14 April 2008
Available online 4 June 2008
Keywords:
Silver(I)
Tetrahedral complexes
Thiosemicarbazones
Sulfur-bridged dinuclear complexes
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
[5–7]. For example, thiosemicarbazone derivatives of copper(II) –
especially with pyridyl substituents at the C2 carbon have proved
Thiosemicarbazones, an important class of N–S donor ligands,
have displayed variable bonding properties in their complexes
and have shown use in a variety of different applications [1–7].
Among coinage metals, copper in its divalent state has been inten-
sively investigated [8,9c], while reports on the chemistry of CuI,
AgI, AuI are limited [9]. Recently, from our lab, several CuI halide
complexes of thiosemicarbazones with triphenylphosphine coli-
gands have been reported [10]. In a recent study of AgI–thiosemi-
carbazone complexes, it was observed that thiosemicarbazone
ligands with alkyl or aryl rings at the C2 carbon have formed halo-
gen bridged dimers, [Ag2(l-X)2(Htsc)2(PPh3)2] {R1 = Ph, R2 = H,
X = Br; R1 = R2 = Me, X = Br; R1 = Ph, R2 = Me, X = Cl, Br, see Chart
1 for substitution patterns of the thiosemicarbazones}, but with
five membered rings such as pyrrole or thiophene, only sulfur-
bridged dimers [Ag2X2(l-S–Htsc)2(PPh3)2] {R1 = pyrrole, R2 = H,
X = Br; R1 = thiophene, R2 = H, X = Cl} were isolated [11]. For
R1 = pyridine, R2 = H, only monomer complexes [AgX(g1-S–
Htsc)(PPh3)2] (X = Cl, Br, I) were isolated [11].
to be more effective as anticancer or antimicrobial agents than
the ligand by itself, probably due to the increased lipophilicity of
the complexes as compared to the free ligand alone [8], and the
complexes have also shown promising results in vivo. In view of
the still limited investigations into the chemistry of silver(I) thio-
semicarbazones as described above, we thus intended to investi-
gate the coordination chemistry of particularly pyridyl based
thiosemicarbazones with silver(I). In the present paper, we inves-
tigate the influence of different combinations of pyridyl, phenyl
and methyl substituents at the C2 carbon of thiosemicarbazones
on the bonding patterns and the nuclearity of complexes with sil-
ver(I) halides and psuedohalides (Chart 1).
2. Experimental
2.1. Materials and techniques
Silver(I) nitrate, silver(I) acetate, sodium chloride, sodium bro-
mide and triphenylphosphine were procured from Aldrich Chemi-
cals Ltd. and used as received. Silver(I) halides (X = Cl, Br) were
freshly prepared by reacting silver(I) nitrate with sodium chloride
or bromide in methanol. 2-Benzoylpyridine thiosemicarbazone
(HL1), 2-acetylpyridine thiosemicarbazone (HL2), benzophenone
thiosemicarbazone (HL3) and acetone thiosemicarbazone (HL4)
The interest into the chemistry of thiosemicarbazone also per-
tains to their utility in the biosciences as anticancer, antibacterial
and antifungal agents and in the analytical field as ion sensors
* Corresponding author. Tel.: +91 183 22 57604; fax: +91 183 22 58820.
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.2008.04.027

2252
T.S. Lobana et al. / Polyhedron 27 (2008) 2251–2258
yellow colored crystals. The complex is highly soluble in CHCl3.
5
(Yellow, 69%, m.p. 185–187 °C). Anal. Calc. for C50H43AgN4O3P2S:
C, 63.17; H, 4.53; N, 5.90. Found: C, 63.03; H, 4.64; N, 6.23%. Main
IR peaks (KBr, cmÀ1): m(N–H) 3458s, 3321s (–NH2–), 3141m (–NH–
); m(NO) 1434s, 1471s, 1369b; m(C@N) + dNH2 + m(C@C) 1608s,
1565s, 1500s; m(C@S) 823s (thioamide moiety); m(C–N) 1184m,
1064s; m(P–CPh) 1094s. The complex is soluble in CHCl3 and par-
tially in CH3CN.
4
3
6
7
R1 =
R2 =
Me
S
H
N
N
1
C
R1
N2
4
1
3
N
C2
NH2
R2
Me
Me
HL4
HL1
HL2
HL3
2.2.4. [Ag(N3,S–HL4)(PPh3)2](NO3) (4)
HL1 = 2-benzoylpyridine thiosemicarbazone
HL2 = 2-acetylpyridine thiosemicarbazone
HL3 = benzophenone thiosemicarbazone
HL4 = acetone thiosemicarbazone
To AgNO3 (0.025 g, 0.15 mmol) in CH3CN (15 mL) was added
HL4 (0.020 g, 15 mmol) and stirring was continued for 2 h. To the
white solid formed was added PPh3 (0.039 g, 0.15 mmol), which
partially cleared the solution. Addition of another mole of PPh3
(0.039 g, 0.15 mmol) resulted in the formation of a clear solution,
which was filtered and kept for crystallization. The complex is sol-
uble in CHCl3. (White, 65%, m.p. 154–156 °C). Anal. Calc. for
Chart 1.
C
40H39AgN4O3P2S: C, 58.14; H, 4.72; N, 6.78. Found: C, 58.42; H,
3.98; N, 6.81% Main IR peaks (KBr, cmÀ1): m(N–H) 3375s, 3325m
(–NH2–), 3186m (–NH–); m(NO) 1359s, 1301b;
m(C@N) + dNH2 + m(C@C) 1645b, 1562s; m(C@S) 823s (thioamide
moiety); m(C–N) 1041s, 1068s; m(P–CPh) 1095s. The complex is sol-
uble in CHCl3 and partially in CH3CN.
were prepared using the literature methods [10a,12]. C, H and N
analyses were obtained with a Thermoelectron FLASHEA1112
CHNS analyzer. Infrared spectra were recorded from KBr pellets
in the range 4000–200 cmÀ1 on a Pye–Unicam SP-3-300 spectro-
photometer. Melting points were determined with a electrically
heated Gallenkamp apparatus. 1H NMR were recorded on a JEOL
AL-300 FT spectrometer operating at a frequency of 300 MHz using
CDCl3 as the solvent with TMS as the internal standard. 31P NMR
spectra were recorded on a Bruker ACP-300 spectrometer operat-
ing at a frequency of 121.5 MHz with H3PO4 as the external stan-
dard with d = 0.
2.2.5. [Ag(N3,S–HL4)(PPh3)2](CH3COO) (5)
To Ag(OOCCH3) (0.025 g, 0.15 mmol) in acetone (15 mL) was
added HL4 (0.020 g, 0.15 mmol) and stirring was continued for
2 h. To the white solid formed, was added PPh3 (0.039 g,
0.15 mmol), which partially cleared the solution. Addition of an-
other mole of PPh3 (0.039 g, 0.15 mmol) resulted in the formation
of a clear solution, which was filtered and kept for crystallization.
The complex is soluble in CHCl3. Crystals were grown from an ace-
tone solution at room temperature. (White, 69%, m.p. 150–152 °C).
Anal. Calc. for C42H42AgN3O2P2S: C, 61.26; H, 5.11; N, 5.43. Found:
C, 61.62; H, 5.55; N, 5.43%. Main IR bands (KBr, cmÀ1): m(N–H)
3285b (–NH2–), 3130m (–NH–); m(C–O)as 1670b, 1585s; m(C–
O)sym 1404b; m(C@N) + dNH2 + m(C@C) 1564s, 1477m; m(C@S) 837s
(thioamide moiety); m(C–N) 1152s, 997s; m(P–CPh) 1093s. The com-
plex is soluble in CHCl3 and CH3CN.
2.2. Synthesis of the complexes
2.2.1. [AgCl(g1-S–HL2)2(PPh3)] (1)
To AgCl (0.025 g, 0.17 mmol) suspended in acetonitrile (15 mL)
was added ligand HL2 (0.034 g, 0.17 mmol), and stirring was con-
tinued for 24 h. To the white solid formed was added solid PPh3
(0.046 g, 0.17 mmol), which partially cleared the solution. Addition
of another mole of PPh3(0.046 g, 0.17 mmol) resulted in the forma-
tion of a clear solution, which was filtered and kept for crystalliza-
tion. Slow evaporation yielded crystals of [AgCl(HL2)2(PPh3)] (1)
along with that of the known [AgCl(PPh3)]4 cubane (50%) which
were manually separated (1 white, 37 %, m.p. 190–192 °C). Anal.
Calc. for C34H35AgClN8PS: C, 51.38; H, 4.41; N, 14.10. Found: C,
51.66; H, 4.89; N, 14.25%. Main IR peaks (KBr, cmÀ1): m(N–H)
3542s, 3427s, 3412m, 3280b (–NH2–), 3153m (–NH–);
m(C@N) + dNH2 + m(C@C) 1585s, 1550s, 1521s; m(C@S) 770s, 836s;
m(C–N) 1050s; m(P–CPh) 1095s. The complex is soluble in CHCl3
and partially in CH3CN.
3. X-ray crystallography
A suitable crystal of complex 1 was mounted on Bruker AXS
SMART APEX CCD diffractometer and likewise crystals of 4 and 5
were mounted on a Bruker APEX II diffractometer with graphite
monochromatised Mo Ka radiation (k = 0.71073 Å). The unit cell
dimensions and intensity data were measured at 100(2) K for 1
and at 273(2) K for 4 and 5. Data were reduced and corrected for
absorption using SMART and SAINT (1) [13a] or XCAD-49 (4 and 5).
The structures were solved by direct methods and refined by full
matrix least squares based on F2 with anisotropic thermal param-
eters for non-hydrogen atoms using SHELXTL (structure solution,
refinement and some molecular graphics). All non-hydrogen atoms
were refined anisotropically. All hydrogen atoms were placed in
calculated positions and were refined with an isotropic displace-
ment parameter 1.5 (methyl) or 1.2 times (all others) that of the
adjacent carbon or oxygen atom.
2.2.2. [Ag2Cl2(l-S–HL1)2(PPh3)2] (2)
Compound 2 was prepared in a similar fashion as compound 1.
(Yellow, 57 %, m.p. 183–185 °C). Anal. Calc. for C62H54Ag2Cl2N8P2S2:
C, 56.20; H, 4.08; N, 8.46. Found: C, 56.60; H, 4.29; N, 8.93%. Main
IR peaks (KBr, cmÀ1): m(N–H) 3417s, 3217s (–NH2–); m(N–H)
3170 cmÀ1; m(C@N) + dNH2 + m(C@C) 1604s, 1602s, 1477s; m(C@S)
816s, 895s; m(C–N) 995s; m(P–CPh) 1096s. The complex is soluble
in CHCl3 and partially in CH3CN.
Suitable light yellow crystals of complexes 2 and 3 were
mounted on a Siemens P4 diffractometer and data were collected
using a scanning mode with graphite monochromatised Mo Ka
radiation (k = 0.71069 Å). Unit cell dimensions and data were col-
lected at 295(2) K. Cell parameters were refined using 25 reflec-
tions in the h range of 1.70–29.96° using XSCANS [13b]. The data
were corrected for Lorentz and polarization effects and a psi-scan
absorption correction was also applied. The structures were solved
2.2.3. [Ag(ONO2)(g1-S–HL3)(PPh3)2] (3)
To AgNO3 (0.025 g, 15 mmol) in CH3CN (15 mL) was added PPh3
(0.076 g, 30 mmol) and stirring was continued at a temperature of
50–60 °C for 2 h. The solid ligand HL3 was added (0.037 g,
15 mmol) to the clear hot solution, and stirring was continued
for another 30 min after switching off heating. The resulting clear
solution was filtered and kept for crystallization to form light

T.S. Lobana et al. / Polyhedron 27 (2008) 2251–2258
2253
Table 1
Crystallographic data for complexes 1–5
1
2
3
4
5
Empirical formula
M.wt.
C
34H35AgClN8PS
C62H54Ag2Cl2N8P2S2
1323.83
C50H43AgN4O3P2S
949.75
C40H39AgN4O3P2S
825.62
C42H42AgN3O2P2S
822.66
794.11
Crystal color
Crystal system
Space group
a (Å)
colorless
triclinic
P1
yellow
pale yellow
triclinic
P1
colorless
monoclinic
P21/c
12.9850(7)
11.2547(6)
26.6850(14)
3870.5(4)
90
97.025(2)
90
4
1.417
0.700
colorless
monoclinic
P21/c
13.078(2)
11.407(2)
26.611(5)
3948.5(12)
90
95.965(3)
90
4
1.384
0.683
triclinic
ꢀ
ꢀ
ꢀ
P1
8.0367(5)
10.7546(7)
21.1659(14)
1780.3(2)
78.391(1)
83.457(1)
88.772(1)
2
11.804(2)
12.208(2)
12.969(2)
1494.6(4)
116.91(1)
92.23(1)
112.04(1)
1
9.658(5)
9.938(5)
24.028(5)
2250.4(17)
89.430(5)
87.890(5)
77.540(5)
2
b (Å)
c (Å)
V (Å3)
a (°)
b (°)
c (°)
Z
Dcalc (Mg mÀ3
)
1.481
0.840
1.471
0.914
1.402
0.612
l(Mo Ka) (mmÀ1
)
Reflections collected
Unique reflections (Rint
Final R indices
18428
8804 (0.0355)
5451
5183 (0.0230)
9454
8491 (0.0460)
59092
9659 (0.0957)
51544
9456 (0.0204)
)
[I P 2rI], R1 and wR2
0.0427, 0.1013
0.0319, 0.0852
0.0364, 0.0949
0.0450, 0.1057
0.0341, 0.0913
by direct methods and refined by Full-matrix least-squares refine-
ment techniques on F2 using SIR-92 and SHELXL-97 [13c]. All non-
hydrogen atoms were refined anisotropically. All hydrogen atoms
were attached geometrically riding on their respective carrier
atoms with Uiso being 1.5, 1.2 and 1.2 times the Uiso of their car-
rier methyl, methylene and aromatic carbon atoms, respectively.
Scattering factors from the International Tables for X-ray crystal-
lography were used [13d]. Data reduction, structure solution,
refinement and drawing of molecular graphics were performed
using SHELXTL-PC [13e] and WINGX [13f]. Table 1 gives crystal data
for complexes.
plexes with different ligand coordination modes, nuclearities and
stoichiometries. An overview of reaction conditions and products
formed is given in Scheme 1.
Silver(I) chloride suspended in acetonitrile slowly reacted with
HL2 (R1 = py and R2 = Me) over a period of 24 h and formed white
insoluble solid and the addition of two moles of triphenylphos-
phine completely dissolved the solid. The clear solution on slow
evaporation at room temperature yielded crystals of tetrahedral
complex [AgCl(HL2)2(PPh3)] 1, with an unusual stoichiometry
(Ag:Htsc:PPh3: 1:2:1) along with crystals of the known cubane
complex, [AgCl(PPh3)]4 [14]. Complex 1 differs from the known
tetrahedral monomers such as [AgCl(g1-S–Hpytsc)(PPh3)2]
6
(Hpytsc = pyridine-2-carbaldehyde thiosemicarbazone) [11]. Reac-
tion of silver(I) chloride with HL1ligand (R1 = py and R2 = Ph) did
not form the similar complex, rather a sulfur-bridged dimer,
[Ag2Cl2(l-S–HL1)2(PPh3)2] 2 along with the known cubane complex
[AgCl(PPh3)]4 were formed. Thus the formation of 2 is analogous to
the more general trend of formation of the sulphur-bridged dimers,
[Ag2X2(l-S–Htsc)2(PPh3)2], {R1 = pyrrole, R2 = H, X = Br; R1 = thio-
phene, R2 = H, X = Cl}, reported in the literature [11]. It is pointed
4. Results and discussion
4.1. Synthesis
Several thiosemicarbazones of the type (R1R2C2@N–NH–
C(@S)N1H2) were reacted with a selection of silver salts (see Chart
1 for the substitution patterns of the ligands). Addition of triphen-
ylphosphine to the reaction mixtures yielded a variety of com-
R
PPh3
Ag
Cl
PPh3
Cl
S
S
Ag
Ag
R
S
Ph3P
S
R
Cl
2
R
S
R
2PPh3
1
2PPh3
S
R
= HL1 2;
R
S
AgX
HL2 1;
HL3 3.
PPh3
S
R
S
R
PPh3
2PPh3
2PPh3
Ag
R
S
(X)
Ag
Ph3P
N3
ONO2
Ph3P
3
S
NH2
4, 5
H
Me
3 N
C
S
N3
=
C
N
S
Me
4, 5
Scheme 1.

2254
T.S. Lobana et al. / Polyhedron 27 (2008) 2251–2258
out here that only 1:1:2 (Ag:Htsc:PPh3) molar ratio yielded the
crystalline products 1 and 2, and stoichiometry of these complexes
is controlled by the nature of the substituents at C2 carbon. Thus
the substitution of the hydrogen atom at the C2 carbon by a methyl
group (sp3 carbon) was able to prevent the binding of a second
PPh3 ligand to the AgI center in case of 1. Introduction of a similarly
bulky phenyl substituent at C2 also did prevent the addition of two
phosphine ligands and no tetrahedral monomeric complex either
similar to 1 or 6 was formed, and instead yielded a sulfur-bridged
dimer, [Ag2Cl2(l-S–HL1)2(PPh3)2] 2. Reaction of HL1 or HL2 with sil-
ver(I) nitrate/acetate led to decomposition and no product could be
identified.
Reaction of silver(I) nitrate or acetate with HL4 (R1 = R2 = Me)
yielded insoluble solids which were reacted with two moles of
phosphine ligands and clear solutions formed on slow evaporation
at room temperature yielded [Ag(N3,S–HL4)(PPh3)2](NO3) 4 and
[Ag(N3,S–HL4)(PPh3)2](CH3COO) 5, with an N3, S-chelation mode
(Scheme 1). Similar bonding was also observed in one mononu-
clear tetrahedral complex, [Cu(HL4)2](Cl) [9a]. Thus with the
methyl substituents at C2 carbon and with the weak binding to sil-
ver by the nitrate or acetate anions vis-à-vis halide ions, HL4ligand
changes conformation from E-mode to Z-mode for chelation to the
metal center.
Fig. 1. Molecular structure of complex 1.
directly or nor via reaction of [AgCl(PPh3)]4 with HL3. Thus the
behaviour of HL3 and HL4 is clearly different, and the nature of
the substituents (Ph, Ph, 3 versus Me, Me, 4, 5) appears to control
the final products.
NH2
S
H
3 N
N
H
Me
Me
C
Me
Me
N
C
3
N
C
C
NH2
S
Z Mode
E Mode
4.2. Structures of complexes
The complexes were analyzed using single crystal X-ray diffrac-
tion. Complexes 1 and 2 crystallized in triclinic crystal system
while complexes 3–5 crystallized in monoclinic system. Complex
2 is dinuclear while other complexes (1, 3–5) are mononuclear.
Table 2 shows important bond parameters and coordination modes
of thiosemicarbazone ligands.
Silver(I) is coordinated by two sulfur atoms, one phosphorus
and one chlorine atoms in mononuclear complex [AgCl(g1-S–
HL2)2(PPh3)] 1(Fig. 1). The uncommon stoichiometry of this com-
plex results in a slight deviation of both bond angles and distances
relative to the commonly known tetrahedral Ag(I) complexes, such
This behaviour of HL4 is different from that with silver(I) bro-
mide which yielded bromo-bridged dimer [Ag2(l-Br)2(HL4)2-
(PPh3)2] [11]. Silver(I) nitrate did not react with the ligand
HL3(R1 = R2 = Ph). Thus silver(I) nitrate was first reacted with tri-
phenylphosphine and to the clear solution was added the HL3 li-
gand. Slow evaporation of the solution yielded crystals of
[Ag(ONO2)(g1-S–HL3)(PPh3)2] 3. Formation of 3 is analogous to
the reaction of copper(I) halides with HL3, wherein analogous tet-
rahedral [CuX(g1-S–HL3)(PPh3)2] (X = Cl, Br) complexes were ob-
tained [10a]. HL3 did not react with silver(I) chloride neither
Table 2
A comparison of important bond distances (Å) and bond angles (°) for complexes 1–5 with other related complexes
Complex
no.
X, (mode)
Ag–S
Ag–X (Ag–P)
P–Ag–P
P–Ag–X
S–Ag–X
P–Ag–S
1
Cl (g1-S)
O (g1-S)
N3 (N3,S)
N3 (N3,S)
Cl (g1-S)
2.5330(7),
2.6113(7)
2.5627(13)
2.6509(7) (2.4178(8))
109.63(2)
101.35(2),
101.01(2)
97.62(7)
129.88(3),
112.35(2)
128.37(4),
100.80(3)
113.43(3),
104.76(4)
105.40(2),
114.13(2)
102.97(2),
117.54(2)
AgÁ Á ÁAg
3
2.557(3) (2.4689(13),
2.4956(10))
2.484(3) (2.4416(9),
2.4625(10))
2.4642(18) (2.4625(7),
2.4800(7))
2.6448(7) (2.4409(7),
2.4879(7))
122.86(3)
129.95(3)
128.155 (19)
120.03(2)
93.80(8), 108.10(7)
109.06(8), 111.98(7)
110.88(5), 111.25(5)
101.98(2), 109.26(2)
P–Ag–X (S–Ag–X)
4
2.5723(10)
2.5618(7)
2.6284(7)
Ag–S
73.31(7)
74.07(4)
102.72(2)
P–Ag–S
5
6 [11]
Ag–X (Ag–P)
Ag–S–Ag,
S–Ag–S
2
Cl (l-S)
Br, (l-S)
Cl, (l-S)
2.6772(10)
2.6715(10)
2.6070(9)
2.6851(9)
2.611(2) 2.876(2)
2.4839(10) (2.4318(10))
2.6857(4) (2.4394(9))
2.520(2) (2.428(18))
88.98(3),
91.02(3)
82.96(2),
97.04(2)
68.33(6),
111.67(6)
127.16(4), 107.21(4)
(104.12(3))
113.66(2), 111.31(2)
(113.66(2))
124.85(6), 106.53(6)
(93.97(3))
102.48(3)
117.08(3)
114.88(3)
112.60(3)
113.45(6)
104.36(6)
3.748(4)
7 [11]
8 [11]
3.5057(0)
3.0902(15)
[AgCl(g1-S–Hpytsc)(PPh3)2] (6) (Hpytsc = pyridine-2-carbaldehyde thiosemicarbazone), [Ag2Br2(l-S–Hptsc)2(PPh3)2] (7) (Hptsc = pyrrole-2-carbaldehyde thiosemicarba-
zone), [Ag2Cl2(l-S–Httsc)2(PPh3)2] (8) (Httsc = thiophene-2-carbaldehyde thiosemicarbazone) [11].

T.S. Lobana et al. / Polyhedron 27 (2008) 2251–2258
2255
as [AgCl(g1-S–Hpytsc)(PPh3)2]
6
(Hpytsc = pyridine-2-carbalde-
hyde thiosemicarbazone) [11]. The packing of complex 1 shows
intermolecular N1HÁ Á ÁCl and N1–HÁ Á ÁS hydrogen bonds forming
1D polymeric chains, which are further interlinked via intermolec-
ular C–HPh–PÁ Á ÁN4(py) hydrogen bonds to form a 2D structure (Fig. 2).
Molecular structure of complex [Ag(ONO2)(g1-S–HL3)(PPh3)2] 3 is
similar to that of related tetrahedral complex 6, except for the pres-
ence of the O-bonded nitrate group in lieu of the chlorine atom
(Fig. 3). The presence of the weakly coordinating nitrate group signif-
icantly alter the bond angles and distances of 3 relative to those of 6
[11]. The packing diagram of 3 shows the presence of intermolecular
–HN1HÁ Á ÁO type of hydrogen bonds between amino and nitrate
groups resulting in a 1D linear chain parallel to the a axis. The linear
chains are further extended into a 2D network by means of CHPhÁ Á ÁS
and CHPhÁ Á ÁONO3 interactions involving phenyl rings of PPh3 (Figs. 4a
and 4b).
The thiosemicarbazone ligand is N3, S-chelated in complex
[Ag(N3,S–HL4)(PPh3)2](NO3) 4 (Fig. 5). The cation is linked to ni-
trate via its C–H(methyl)Á Á ÁO, N2-HÁ Á ÁO and N1–HÁ Á ÁO hydrogen
bonds. Two units of 4 combine via second N1–HÁ Á ÁO hydrogen
bonds forming a dimer (Fig. 6). The bonding and packing pattern
of [Ag(N3,S–HL4)(PPh3)2](CH3COO)] 5 is similar to 4.
Finally the dinuclear complex [Ag2Cl2(l-S–HL1)2(PPh3)2] 2 is
sulfur bridged and its central Ag2(l-S)2Ag core forms a parallelo-
gram. Each silver atom is further coordinated to a terminal chlo-
rine and one P atom of PPh3 (Fig. 7). The bond parameters and
core angles are comparable to other sulfur-bridged dimers re-
ported in the literature (Table 2) [11]. Complex 2 shows the pres-
ence of intramolecular –HN1HÁ Á ÁCl and N2HÁ Á ÁN4 hydrogen bonds
and two dimeric molecules are further linked via short CHÁ Á ÁCl
contacts involving phenyl rings of PPh3 resulting in 1D polymeric
chain. The chain is extended in 2D via intermolecular CHÁ Á Áp inter-
actions (Fig. 8).
Fig. 2. Packing diagram of complex 1.
5. IR and NMR spectral studies
IR spectroscopy of all complexes confirmed the presence of the
individual ligands and counterions via their m(N–H), m(C–N),
m(C@C), m(C@N), and m(N–O), m(P–C) vibrational modes. The
m(C@S) thioamide bands are located at 770–837 cmÀ1, which sug-
gests (in agreement with the X-ray data) a significant weakening
of the C@S double bond in all complexes. The 1H NMR spectra of
complexes 1–4 reveal the presence of -N2H, –N1H2, methyl and
ring proton signals generally at low field relative to their corre-
sponding free ligands (Table 3). The 31P NMR spectra of tetrahedral
complexes1, 3–5 showed coordination shifts (dcomplex À dligand
comparable to the literature reports on tetrahedral silver(I)–thio-
semicarbazone complexes [11]. An additional band at
)
d
30.81 ppm in 3 reveals the formation of another species, probably
a sulfur-bridged dimer in the solution state.
Fig. 3. Molecular structure of complex 3. (Hydrogen atoms have been omitted for
clarity.)
À
Fig. 4a. Formation of a 1D linear chain due to amine N1 and NO3 hydrogen bonding interactions parallel to a axis.

2256
T.S. Lobana et al. / Polyhedron 27 (2008) 2251–2258
Fig. 4b. Formation of a 2D network in the ab plane of complex 3.
6. Conclusion
The substituents at C2 carbon appear to control the stoichiome-
try, nuclearity and dentacy of thiosemicarbazone complexes of sil-
ver(I) salts. For R1 = pyridyl and R2 = H, only tetrahedral monomers,
[AgCl(g1-S–Hpytsc)(PPh3)2] (X = Cl 6) were formed [11]. The sub-
stitution of the hydrogen atom at the C2 carbon by a methyl group
(sp3 carbon) (R1 = pyridyl and R2 = Me) was able to prevent the
binding of a second PPh3 ligand to the AgIcenter in case of 1 and
formed complex [AgCl(HL2)2(PPh3)] 1, with an unusual stoichiom-
etry (1:2:1: Ag:Htsc:PPh3). Introduction of a similarily bulky phe-
nyl substituent at C2 also did prevent the addition of two
phosphine ligands, and presumably formed three coordinate spe-
cies, {AgCl(HL1)(PPh3)} which dimerised to yield a sulfur-bridged
dinuclear complex, [Ag2Cl2(l-S–HL1)2(PPh3)2] 2, and no tetrahedral
monomeric complex either similar to 1 or 6 was formed. The pres-
ence of both the methyl groups at C2 carbon (R1 = R2 = Me, HL4) fa-
vored N3, S-chelation in 4 and 5, and this property of HL4 is
supported by chelation in [Cu(HL4)2]Cl reported in the literature
[9a]. Also when the anion is more tightly bonded to the metal cen-
Fig. 5. Molecular structure of complex 4 (complex 5 has a similar structure).
Fig. 6. Packing diagram of complex 4.

T.S. Lobana et al. / Polyhedron 27 (2008) 2251–2258
2257
ter as in silver(I) bromide, this ligand yielded a bromo-bridged di-
mer, [Ag2(l-Br)2(g1-S–HL4)2(PPh3)2] [11]. With both phenyl groups
at C2 carbon (R1 = R2 = Ph, HL3), only tetrahedral complexes of more
common stoichiometry, [Ag(ONO2)(g1-S–HL3)(PPh3)2]
3
or
[CuCl(g1-S–HL3)(PPh3)2] [10a] are formed.
In short stoichiometry, dentacy and nuclearity of coinage me-
tal complexes with thiosemicarbazones is influenced by the sub-
stituents at C2 carbon, and also by the nature of the anion/metal.
The chelation by neutral thiosemicarbazones is limited and apart
from three examples discussed in this paper, there are only two
more examples of chelation by neutral thiosemicarbazones
[11,15].
Acknowledgements
Financial assistance from CSIR, New Delhi (F.No.9/254(159)/
2005-EMR-I) and research facilities to one of us (Sonia) by the uni-
versity are gratefully acknowledged. The authors thank Matthias
Zeller of Youngstown State University, USA for his useful sugges-
tions and in X-ray crystallography.
Fig. 7. Molecular structure of complex 2.
Fig. 8. Packing diagram of complex 2.
Table 3
NMR data (d, ppm) for complexes 1–5
Compound
1H NMR
–N2H
31P (Dd)
–N1H2
CH3
Ligand protons
[AgCl(g1-S–HL2)2(PPh3)] 1
[Ag2Cl2(l-S–HL1)2(PPh3)2] 2
14.79b 9.24b
2.49s,
2.14s
8.76d, 8.61d (C7H); 7.57d, 7.95d (C4H); 7.72–7.75m (C5,6H); 7.30–7.44m
(Ph + N1H2)
6.55 (11.2)
14.07s 9.52s,
7.67b,
8.83d (C7H); 7.81td (C6H); 7.30–7.61m (Ph + C4,5H)
11.21 (15.9)
[Ag(ONO2)(g1-S–HL3) (PPh3)2]
9.20s
8.55sb
7.27–7.70m (Ph + N1H2)
7.25–7.43m (Ph + N1H2)
7.27–7.70m (Ph + N1H2)
30.81 (35.51) 2.74
(7.44)
8.8 (13.5)
3
[Ag(N3,S–HL4)(PPh3)2] (NO3) 4
11.64s
1.98s,
1.91s
2.17s,
2.01s
[Ag(N3,S–HL4)(PPh3)2]
7.3 (12.0)
(CH3COO) 5a
HL1
HL2
13.86s 8.56s
8.23d (C7H); 7.77td (C6H); 7.30–7.56m (N1H2 + Ph + C5H); 7.31d (C4H)
8.77d, 8.62d (C7H); 7.97d, 7.54d (C4H); 7.55–7.92m (N1H2 + C5, 6H)
14.7s
8.86sb
2.44s,
2.40s
HL3
HL4
8.68s
8.44s
7.81s, 7.45s
7.27s,
7.27–7.61m (Ph)
2.02s,
1.91s
6.19sb
a
It did not show this –N2H signal probably due to its exchange with the acetate anion in solution.

2258
T.S. Lobana et al. / Polyhedron 27 (2008) 2251–2258
[7] (a) M.B. Ferrari, G.G. Fava, P. Tarasconi, R. Albertini, S. Pinelli, R. Starcich, J.
Appendix A. Supplementary data
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CCDC 673439, 666768, 658221, 673440 and 673441 contain the
supplementary crystallographic data for 1, 2, 3 and 4. These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/con-
ts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk. See supplementary
for bond parameters, X-ray figures and packing diagrams of various
complexes. Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.poly.2008.04.027.
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