Synthesis, X-ray crystal structures and properties of complex salts and sterically crowded heteroleptic complexes of group 10 metal ions with aromatic sulfonyl dithiocarbimates and triphenylphosphine ligand

Article abstract of DOI:10.1016/j.ica.2010.07.065

Two new complex salts of the form (Bu₄N)₂[Ni(L) ₂] (1) and (Ph₄P)₂[Ni(L)₂] (2) and four heteroleptic complexes cis-M(PPh₃)₂(L) [M = Ni(II) (3), Pd(II) (4), L = 4-CH₃OC₆H₄SO ₂NCS₂] and cis-M(PPh₃)₂(L′) [ M = Pd(II) (5), Pt(II) (6), L′ = C₆H₅SO ₂NCS₂] were prepared and characterized by elemental analyses, IR, ¹H, ¹³C and ³¹P NMR and UV-Vis spectra, solution and solid phase conductivity measurements and X-ray crystallography. A minor product trans-Pd(PPh₃)₂(SH) ₂, 4a was also obtained with the synthesis of 4. The NiS₄ and MP₂S₂ core in the complex salts and heteroleptic complexes are in the distorted square-plane whereas in the trans complex, 4a the centrosymmetric PdS₂P₂ core is perforce square planar. X-ray crystallography revealed the proximity of the ortho phenyl proton of the PPh₃ ligand to Pd(II) showing rare intramolecular C-H?Pd anagostic binding interactions in the palladium cis-5 and trans-4a complexes. The complex salts with σ_rt values ～10^-5 S cm^-1 show semi-conductor behaviors. The palladium and platinum complexes show photoluminescence properties in solution at room temperature.

Full text of DOI:10.1016/j.ica.2010.07.065

Inorganica Chimica Acta 363 (2010) 3589–3596
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis, X-ray crystal structures and properties of complex salts and
sterically crowded heteroleptic complexes of group 10 metal ions with
aromatic sulfonyl dithiocarbimates and triphenylphosphine ligand
a
b
c
Nanhai Singh a, , Bandana Singh , Kamlesh Thapliyal , Michael G.B. Drew
*
a Department of Chemistry, Banaras Hindu University, Varanasi 221 005, UP, India
b Chemistry Department, IIT Kanpur, Kanpur 208 016, India
c Department of Chemistry, University of Reading, Whiteknights, Reading RG6 6AD, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 June 2010
Received in revised form 3 July 2010
Accepted 12 July 2010
Available online 25 July 2010
Two new complex salts of the form (Bu4N)2[Ni(L)2] (1) and (Ph4P)2[Ni(L)2] (2) and four heteroleptic
complexes cis-M(PPh3)2(L) [M = Ni(II) (3), Pd(II) (4), L = 4-CH3OC6H4SO2N@CS2] and cis-M(PPh3)2(L0)
[M = Pd(II) (5), Pt(II) (6), L0 = C6H5SO2N@CS2] were prepared and characterized by elemental analyses,
IR, 1H, 13C and 31P NMR and UV–Vis spectra, solution and solid phase conductivity measurements and
X-ray crystallography. A minor product trans-Pd(PPh3)2(SH)2, 4a was also obtained with the synthesis
of 4. The NiS4 and MP2S2 core in the complex salts and heteroleptic complexes are in the distorted
square-plane whereas in the trans complex, 4a the centrosymmetric PdS2P2 core is perforce square pla-
nar. X-ray crystallography revealed the proximity of the ortho phenyl proton of the PPh3 ligand to Pd(II)
showing rare intramolecular C–Hꢀ ꢀ ꢀPd anagostic binding interactions in the palladium cis-5 and trans-4a
complexes. The complex salts with rrt values ꢁ10ꢂ5 S cmꢂ1 show semi-conductor behaviors. The palla-
dium and platinum complexes show photoluminescence properties in solution at room temperature.
Ó 2010 Elsevier B.V. All rights reserved.
Keywords:
Dithiocarbimate
Complex salts
Heteroleptic
Semi-conductor
Photoluminescence
1. Introduction
the ligand dithiocarbimate are important because of their resem-
blance to dithiocarbamate complexes which have been extensively
Group 10 metal complexes with unsaturated dianionic 1,1- and
1,2-dithioligands where thio functions are present on the same or
neighboring carbons have been the main focus of research for the
design and study of molecular conductors [1–5]. The higher con-
ductivities of sulfur rich complexes are mainly due to their highly
extended delocalized Sꢀ ꢀ ꢀS/Mꢀ ꢀ ꢀS intermolecular stacked struc-
tures which they exhibit in the solid state. On the other hand,
the heteroleptic complexes of platinum(II) with 1,1- or 1,2-dithio
ligands containing polypyridyl [6] and less often phosphine ligands
[7] have emerged as an interesting class of room temperature solu-
tion and fluid state luminescent materials which make them
important candidates as photocatalyst in light driven reactions
[6]. The incorporation of phosphine ligands into the platinum
group metal complexes brings remarkable changes in structural
and electronic rearrangements, chemical reactivity and physical
studied and are well known to exhibit a variety of useful applica-
tions [8–21].
The three important features associated with the aromatic sul-
fonyl dithiocarbimate ligands are (i) the delocalization that this li-
gand can provide beyond M–S2 bonds through C@N, C–S and Ar–
SO2–N groups (ii) the high electron density presented by the sulfur
donors and (iii) the presence of several hard and soft donor atoms
N, O and S in the molecule. This makes a significant difference in
the structure and properties of their complexes. Thus aromatic sul-
fonyl dithiocarbimates can be used as important scaffolds for the
synthesis of complex salts and heteroleptic complexes. Despite this
synthetic versatility [22,23] and the fact that various important
properties have been established for the metal complexes that
can be formed, scant attention has been paid to this ligand system
and only recently the coordination chemistry and some of their
applications have been exploited [24–28].
Given these facts we have concentrated our research efforts in
this important area and report here the synthesis, crystal structure,
molecular electrical conducting and photoluminescent properties
of some hitherto uninvestigated complex salts and heteroleptic
complexes of nickel(II), palladium(II) and platinum(II) with the li-
gands dithiocarbimate and triphenylphosphine.
properties because of their large steric demands as well as
and -acceptor properties.
r-donor
p
The dianionic 1,1-dithiocarbimate ligand is akin to the unian-
ionic 1,1-dithiocarbamate (dtcꢂ) ligand (Scheme 1). Complexes of
* Corresponding author. Fax: +91 542 2368127.
E-mail addresses: nsingh@bhu.ac.in, nanhai_singh@yahoo.com (N. Singh).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.07.065

3590
N. Singh et al. / Inorganica Chimica Acta 363 (2010) 3589–3596
O
sym(CS2), 376 m
(Ni–S). 1H NMR (300.40 MHz, DMSO-d6, ppm): d
-
-
O
R
S
S
-
7.98 (d, J = 7.2 Hz, 4H, H2 and H6), 6.99 (d, J = 8.1 Hz, 4H, H3 and
H5), 3.80 (3H, –OCH3), 7.81–7.62 (m, 40H, PPh4þ). 13C
(75.45 MHz, DMSO-d6, ppm): d 208.97 (N@CS2), 161.33 (C4),
135.41 (C1), 129.03 (C2 and C6), 113.23 (C3 and C5), 55.44
S
H3CO
S
+
C
N
N
C
-
S
R
4-methoxyphenyl-
sulfonyldithiocarbimate2-
(–OCH3); 135.37 (C40), 134.65 (C30 and C50), 130.41 (C20 and C60),
dtc-
117.11 (C10) PPh4
. d
31P {1H}NMR (121.50 MHz, DMSO-d6):
þ
24.32 ppm. UV–Vis (CH2Cl2, kmax
, nm, e,
Mꢂ1 cmꢂ1): 273
Scheme 1. Structure of ligands.
(3.43 ꢃ 104), 309 (3.66 ꢃ 104), 322 (3.63 ꢃ 104), 355 (3.41 ꢃ 104),
430 (3.97 ꢃ 104), 477 (0.5 ꢃ 103) and 608 (97). KM (DMSO,
ꢂ1 cm2 molꢂ1): 36.6.
r
rt = 2.55 ꢃ 10ꢂ5 S cmꢂ1, Ea = 0.57 eV.
2. Experimental
X
2.1. Material and reagents
2.3.3. Synthesis of Ni(PPh3)2L (3)
To a stirred 25 ml methanolic solution of PPh3 (0.524 g, 2 mmol)
was added gradually, 15 ml aqueous-methanolic (1:2) solution of
the ligand K2Lꢀ2H2O (0.375 g, 1 mmol). To this solution, solid
NiCl2ꢀ6H2O (0.237 g, 1 mmol) was added and stirred continuously
for 6 h. The peach color solid product thus formed was filtered
off and washed with the same solvent mixture followed by diethyl
ether and dried in vacuo over CaCl2.
All reactions were carried out in open atmosphere at ambient
temperature. Chemicals were procured from Merck and Sigma
Aldrich and used without further purification. The solvents were
distilled and dried before use where necessary. Potassium salts of
the ligands, L and L0, 4-methoxyphenylsulfonyl and phenylsulfonyl
dithiocarbimate (4-CH3OC6H4SO2N@CS2K2ꢀ2H2O and C6H5SO2N
CS2K2ꢀ2H2O) were prepared according to the literature method
[29,30] by the reaction of corresponding sulfonamides, potassium
hydroxide and carbon disulfide in dimethylformamide and charac-
terized by elemental analyses, IR, 1H, 13C and 31P NMR spectra.
Yield: (0.692 g, 82%), M.P. 171–173 °C.
Anal. Calc. for
C44H37S3O3NP2Ni: C, 62.63; H, 4.42; N, 1.66; S, 11.38, Ni, 6.87.
Found: C, 62.25; H, 4.38; N, 1.64; S, 10.8, Ni, 6.65%. IR (KBr,
cmꢂ1): 1410
sym(CS2) 384
m
m
(C@N); 1257
masym(SO2); 1147 msym(SO2); 925 ma-
(Ni–S). 1H NMR (300.40 MHz, CDCl3, ppm): d 7.76
2.2. Physical measurements
(d, J = 9.00 Hz, 2H, H2 and H6), 6.78 (d, J = 8.70 Hz, 2H, H3 and
H5), 3.82 (3H, –OCH3), 7.60–7.16 (m, 30H, PPh3). 13C (75.45 MHz,
CDCl3, ppm): d 202. (N@CS2), 161.83 (C4); 133.95 (C1), 128.35
(C2 and C6); 113.16(C3 and C5); 55.40 (-OCH3); 132.31 (C20 and
C60); 131.89 (C40), 129.90 (C10), 128.35 (C30 and C50) PPh3. 31P
Experimental details pertaining to the elemental analyses,
recording of IR, UV–Vis, photoluminescence and NMR spectra,
measurements of solution and pressed pellet conductivity of the
complexes are same as described earlier [4,19–21].
{1H} NMR (121.50 MHz, CDCl3): d 34.88 ppm. UV–Vis (CH2Cl2, kmax
,
nm,
e,
Mꢂ1 cmꢂ1): 234 (0.29 ꢃ 104); 294 (3.73 ꢃ 104), 310
2.3. Synthesis
(3.72 ꢃ 104), 345 (3.56 ꢃ 104), 425 (2.2 ꢃ 104), 475 (0.58 ꢃ 104)
and 597 (50).
2.3.1. Synthesis of (NBu4)2[Ni(L)2] (1)
To a stirring 15 ml aqueous-methanol (2:1) solution of the li-
gand K2Lꢀ2H2O (0.750 g, 2 mmol) solid NiCl2ꢀ6H2O (0.237 g,
1 mmol) was added, followed by 10 ml methanolic solution of
NBu4I (0.738 g, 2 mmol). The reaction mixture was then stirred
for 6 h at room temperature. The green color precipitate thus
formed was filtered off, washed with the same solvent mixture fol-
lowed by diethyl ether and dried in vacuo over CaCl2.
2.3.4. Synthesis of Pd(PPh3)2L (4)
Complex 4 was prepared and isolated as described for complex
3 using K2PdCl4 (0.326 g, 1 mmol), PPh3 (0.524 g, 2 mmol) and
K2Lꢀ2H2O (0.375 g, 1 mmol) and continuously stirred for about
30 h. The yellow solid product isolated was dissolved in
CH2Cl2:CH3CN mixture. After one week, from the slow evaporation
of the solvent, block shaped crystals of Pd(PPh3)2L 4 and needle
shaped crystals of Pd(PPh3)2(SH)2 4a were obtained.
Yield: (0.831 g, 78%), M.P. 122–125 °C. Anal. Calc. for
C
48H86S6O6N4Ni: C, 54.07; H, 8.13; N, 5.25; S, 18.04; Ni, 5.50.
Found: C, 53.84; H, 8.10; N, 5.21; S, 17.7; Ni, 5.48%. IR (KBr,
cmꢂ1): 1395
(C@N), 1262 asym(SO2); 1136 sym(SO2); 940
asym(CS2), 384
(Ni–S). 1H NMR (300.40 MHz, DMSO-d6, ppm): d
Yield: (0.669 g, 75%), M.P. 205–207 °C,
44H37S3O3NP2Pd: C, 59.23; H, 4.18; N, 1.57; S, 10.78. Found: C,
58.82; H, 4.07; N, 1.54; S, 10.24%. IR (KBr, cmꢂ1): 1445
(C@N);
1257 (SO2ass); 1145 (SO2sym); 922 (CS2), 377
(Pd–S). 1H NMR
Anal. Calc. for
C
m
m
m
m
m
m
m
m
m
m
7.66 (d, J = 8.79 Hz, 4H, H2 and H6), 6.99 (d, J = 8.79 Hz, 4H, H3
and H5), 3.81 (3H, OCH3): 0.95 (t, 24H, CH3), 1.37–1.14 (m, 16H,
(300.40 MHz, CDCl3, ppm): d 7.83 (d, J = 9 Hz, 2H, H2 and H6),
6.8 (d, J = 8.7 Hz, 2H, H3 and H5), 7.44–7.19 (m, 30H, PPh3), 3.83
(3H, –OCH3). 13C (75.45 MHz, CDCl3, ppm): d 201.35 (N@CS2),
161.97 (C4), 135.07 (C1), 129.26 (C2 and C6,; 113.12 (C3 and
C5); 55.39 (–OCH3); 134.53 (C20 and C60), 130.85 (C40), 129.57
(C10), 128.47 (C30 and C50) PPh3. 31P {1H}NMR (121.50 MHz, CDCl3):
þ
CH2), 1.63–1.53 (m, 16H, CH2), 3.81–3.15 (m, 16H, CH2N), NBu4
.
13C (75.45 MHz, DMSO-d6, ppm): d 209.39 (N@CS2), 161.78 (C4),
135.85 (C1), 129.44 (C2 and C6), 113.66 (C3 and C5), 55.89
(–OCH3); 58.08(N–CH2), 23.57 (CH2), 19.69 (CH2), 13.96 (CH3)
NBu4þ. UV–Vis (CH2Cl2, kmax, nm,
e
, Mꢂ1 cmꢂ1): 277 (3.47 ꢃ 104),
d 31.04 ppm. UV–Vis (CH2Cl2, kmax, nm, e,
Mꢂ1 cmꢂ1): 273
319 (3.70 ꢃ 104), 348 (3.45 ꢃ 104), 428 (3.94 ꢃ 104), 465
(3.5 ꢃ 104), 307 (3.71 ꢃ 104), 364 (3.46 ꢃ 104).
(1.14 ꢃ 103) and 610 (94). KM (DMSO (
X
ꢂ1 cm2 molꢂ1): 38.2.
r
rt = 4.97 ꢃ 10ꢂ5 S cmꢂ1, Ea = 0.56 eV.
2.3.5. Synthesis of Pd(PPh3)2 (SH)2 (4a)
M.P. 235–240 °C. Anal. Calc. for C36H32P2S2Pd: C, 62.06; H, 4.63;
S, 9.19. Found: C, 61.85; H, 4.60; S, 8.82%. 31P {1H} NMR
(121.50 MHz, CDCl3): d 24.04 ppm.
2.3.2. Synthesis of (PPh4)2[Ni(L)2] (2)
The yellowish green complex 2 was prepared and isolated as
described for complex 1 using PPh4Cl (0.750 g, 2 mmol), NiCl2?6-
H2O (0.237 g, 1 mmol) and the ligand K2L?2H2O (0.750 g, 2 mmol).
2.3.6. Synthesis of Pd(PPh3)2L0 (5)
Yield: (0.945 g, 75%), M.P. 210–212 °C.
64H54S6O6N2P2Ni: C, 61.00; H, 4.32; N, 2.22; S, 15.26; Ni, 4.66.
Found: C, 60.51; H, 4.27; N, 2.20; S, 14.81; Ni, 4.61%. IR (KBr,
cmꢂ1): 1385
(C@N), 1255 asym(SO2); 1140 sym(SO2); 945 ma-
Anal. Calc. for
The yellow complex 5 was prepared and isolated as described
for complex 3 using K2PdCl4 (0.326 g, 1 mmol), PPh3 (0.524 g,
2 mmol) and K2L0?2H2O (0.346 g, 1 mmol) and continuously stir-
ring the reaction mixture for about 30 h.
C
m
m
m

N. Singh et al. / Inorganica Chimica Acta 363 (2010) 3589–3596
3591
Yield: (0.707 g, 82%), M.P. 168–170 °C. Anal.
43H35P2S3O2NPd: C, 59.89; H, 4.09; N, 1.62; S, 11.15. Found: C,
59.35; H, 4.06; N, 1.59; S, 10.86%. IR (KBr, cmꢂ1): 1433
(C@N);
1300 masym (SO2); 1143 sym(SO2); 992 asym(CS2), 368
(Pd–S). 1H
Calc. for
3. Results and discussion
C
m
3.1. Synthesis
m
m
m
NMR (300.40 MHz, CDCl3, ppm): d 7.90 (d, J = 7.80 Hz, 2H, H2
and H6), 7.75–7.17 (m, 33H, H3, H4, H5 and PPh3). 13C (75.45
MHz, CDCl3, ppm): d 207.04 (N@CS2), 142.14 (C1), 132.18 (C4),
129.55 (C3 and C5), 127.81 (C2 and C6); 134.32 (C10), 132.45 (C20
and C60), 128.95 (C30 and C50), 127.99 (C40) PPh3. 31P {1H} NMR
Treatment of an in situ generated complex salt K2[Ni(L)2] with
the NBu4I or PPh4Cl salt resulted in the formation of the complex
salts (NBu4)2[Ni(L)2] and (PPh4)2[Ni(L)2]. The heteroleptic com-
plexes M(PPh3)2L and M(PPh3)2L0 [L = p-methoxyphenylsulfonyl
dithiocarbimate, L0 = phenylsulfonyldithiocarbimate; M = Ni(II),
Pd(II) or Pt(II)] were obtained in identical conditions by the single
pot reaction of the metal salts with the dithiocarbimate ligands
and PPh3 in required molar ratios according to reactions detailed
in Scheme 2.
(121.50 MHz, CDCl3): d 29.87 ppm. UV–Vis (CH2Cl2, kmax, nm, e,
Mꢂ1cmꢂ1): 248 (3.8 ꢃ 104), 292 (3.47 ꢃ 104), 302(3.48 ꢃ 104),
326 (3.57 ꢃ 104), 420 (0.386 ꢃ 104).
Although reaction of PPh3 with K2PdCl4 and the ligand p-meth-
oxyphenylsulfonyl dithiocarbimate gives high yield of the cis-prod-
uct 4, somewhat,fortuitously reaction (iv) gives crystals of trans-
Pd(PPh3)2(SH)2, 4a as a minor species. This reaction to form 4a pos-
sibly proceeds [34] via the minor precursor complex trans-
Pd(PPh3)2Cl2 [35,36] formed during the course of the reaction
according to Scheme 3.
2.3.7. Synthesis of Pt(PPh3)2L0 (6)
The colorless complex 6 was synthesized and isolated as de-
scribed for complex 3 using K2PtCl4 (0.415 g, 1 mmol), PPh3
(0.524 g, 2 mmol) and K2L0ꢀ2H2O (0. 346 g, 1 mmol) and continu-
ously stirred for 48 h.
Yield: (0.751 g, 79%), M.P. 193–195 °C,
43H35P2S3O2NPt: C, 54.31; H, 3.71; N, 1.47; S, 10.11. Found: C,
53.9; H, 3.66; N, 1.46; S, 9.85%. IR (KBr, cmꢂ1): 1429
(C@N);
1305 asym(SO2); 1138 sym(SO2); 997 asym(CS2), 382
(Pt–S). 1H
Anal. Calc. for
The complexes were characterized by elemental analyses, IR,
electronic absorption, 1H, 13C and 31P NMR spectra and the single
crystal X-ray diffraction. All are air stable solids; except 3 which
melts at 171 °C, the remaining complexes melt with decomposi-
tion in the temperature range 122–240 °C. They are soluble in
the common organic solvents such as methanol, ethanol, dichloro-
methane, acetonitrile, dimethylsulfoxide and dimethylformamide.
C
m
m
m
m
m
NMR (300.40 MHz, CDCl3, ppm): d 7. 89 (d, J = 7.2 Hz, 2H, H2 and
H6), 7.43–7.173 (m, 33H, H3, H4, H5 and PPh3); 13C (75.45 MHz,
CDCl3, ppm):
d 208.24 (N@CS2); 145.01(C1); 133.53 (C4),
129.14(C3 and C5); 127.84 (C2 and C6); 135.15 (C10); 132.87(C20
The solution conductivity 38.2 and 36.6
X
ꢂ1 cm2 molꢂ1 for 1 and
and C60); 129.20(C30 and C50); 127.96 (C40) PPh3. 31P {1H} NMR
(121.50 MHz, CDCl3):
2, respectively, in 10ꢂ3 M DMSO solution show their ionic nature;
the heteroleptic complexes are non-electrolytes [37]. Their solid
phase electrical conductivity and qualitative solution photolumi-
nescent properties have been studied.
d
17.67, 1J(195Pt–31P) = 3125 Hz. UV–vis
(CH2Cl2, kmax, nm,
e
, Mꢂ1 cmꢂ1): 261(3.8 ꢃ 104), 301(3.57 ꢃ 104),
323 (3.51 ꢃ 104), 358 (3.45 ꢃ 104).
2.4. X-ray diffraction studies
3.2. Spectroscopy
Single crystal X-ray data, the space group, unit cell dimensions
and intensity data for the complexes were collected on Oxford Dif-
fraction X-Calibur CCD (1, 2, 5, 6) and Bruker Smart Apex (3, 4a)
The structure of the dithiocarbimate ligand given in Scheme 1
plays an important role in the description of the bonding behavior
of this ligand in the complexes. In the infrared spectra the absorp-
tions at 1385–1445, 1255–1305, 1136–1147, 922–997 and 368–
diffractometers using graphite monochromated Mo K
a radiation.
The crystals were mounted on glass fiber. The structures were
solved by the direct method using SHELXS-97 [31] and refined aniso-
tropically for non-hydrogen atoms by full matrix least-squares
technique using SHELXL-97 [31]. All the hydrogen atoms were geo-
metrically fixed with thermal parameters equivalent to 1.2 times
that of the atom to which they were bonded. PLATON [32] was used
for analyzing the weak interactions, bond distances and angles.
Diagrams for all complexes were prepared using ORTEP [33].
384 cmꢂ1 are characteristic of
sym(CS2), and
t
(C@N),
tasym(SO2), tsym(SO2), ta-
t
M–S vibrations, respectively [34]. A significant
enhancement in the C@N stretching frequency of the complexes
by comparison with the free dithiocarbimates ca. 1260 cmꢂ1 sug-
gests (S,S) coordination of the ligands.
The 1H and 13C NMR spectra of the complexes in DMSO-d6 dis-
play characteristic resonances for the NBu4þ- and PPh4þ-cations
and the ligand dithiocarbimate functionalities as well. The ob-
CH3OH : H2O
CH3OH : H2O
(i)
K2[Ni(L)2] + 2KCl
NiCl2 + 2 K2L
K2[Ni(L)2] + 2 NBu4I / 2 PPh4Cl
(NBu4)2[Ni(L)2](1)/(PPh4)2[Ni(L)2](2)
(ii)
+ 2KI / 2KCl
CH3OH : H2O
cis-M(PPh3)2L / L' + 2KCl / 4KCl (iii)
NiCl2 / K2MCl4 + K2L / L' + 2PPh3
[M = Ni (3), L = 4-CH3OC6H4SO2N=CS2;
M = Pd (5), Pt (6), L' = C6H5SO2N=CS2]
cis-Pd(PPh3)2L (4)
+ 4KCl
CH3OH : H2O
K2PdCl4 + K2L + 2 PPh3
(iv)
trans- Pd(PPh3)2(SH)2
(4a)
Scheme 2. Synthesis of the complexes.

3592
N. Singh et al. / Inorganica Chimica Acta 363 (2010) 3589–3596
O
not be confirmed in solution because the anticipated down field
shift for the ortho-proton of the phenyl ring of the ligand PPh3 in-
volved in the interactions is not distinguishable as the ligand dithi-
carbimate signals also occur in the same region.
PPh3
Pd
O
-
S
S
OCH3
C
N
+
Cl
Cl
-
S
PPh3
CH3OH : H2O
3.3. X-ray crystallography
Single crystals of the complexes 1 and 2 were obtained by slow
evaporation of CH3OH:H2O; those of 3, 4, 4a, 5 and 6 were grown in
CH2Cl2:CH3CN solvent. Crystal data and structure refinement de-
tails for 1, 2, 4a and 5 are given in Table 1. ORTEP plots showing
the structures of the four complexes are presented in Figs. 1–4,
respectively, and selected bond distances and angles are included
in Tables 2–4. Complex 1 contains [NBu4]+ and 2 contains [PPh4]+
cations, both in general positions together with [Ni(L)2]2ꢂ anions
in which the metal atoms are situated on crystallographic centers
of symmetry. The immediate square planar geometry around the
nickel atom in the complex anion of 1 and 2 (Figs. 1 and 2) is de-
fined by the coordination of four sulfur atoms from the 4-meth-
oxyphenylsulfonyl dithiocarbimate ligand. The Ni(1)–S(1) and
Ni(1)–S(2) bond lengths are 2.2057(6), 2.1883(6) Å in 1 and
2.2034(5), 2.2091(5) Å in 2, respectively. The bite angles S(1)–Ni–
S(2), 78.64(2)° and 78.37(2)° in 1 and 2, respectively, show consid-
erable deviation from the idealized 90° square planar geometry.
The atoms Ni, S(1), S(2) and C(2) show very small deviations
0.017, ꢂ0.023, ꢂ0.023 and 0.028 Å in 1 and 0.031, ꢂ0.042,
ꢂ0.042 and 0.052 Å in 2 from the least-squares plane of the chelate
ring. Within the NiS2C core the Ni–S–C angles are 87.03(7)–
87.32(7)° in 1 and 86.96(6)–87.15(6)° in 2 and the S(1)–C(3)–S(2)
angles are 106.9(3)° and 107.1(1)° in 1 and 2, respectively.
The structure of 4a (Fig. 3) contains discrete trans-
Pd(PPh3)2(SH)2 molecules. The palladium atom lies on a crystallo-
graphic center of symmetry and has a four-coordinate square pla-
nar geometry. Pd–S and Pd–P distances are 2.2924(3) and
2.332(2) Å, respectively. The S–Pd–P angles are close to 90°.
In 5 the Pd atom has a four-coordinate square planar environ-
ment being bonded to two phosphorus atom of PPh3 ligands and
atoms S(1) and S(2) of the bidentate L0 ligand (Fig. 4). The P(1)–
Pd–S(1) and P(1)–Pd–S(2) angles are less distorted from the 90°
than the P(1)–Pd–P(2) and S(1)–Pd–S(2) angles due to both the ste-
O
S
O
N
PPh3
Pd
PPh3
Pd
C
S
S
S
PPh3
PPh3
n
S
Hydrolysis
O
PPh3
Pd
O
O
OCH3
+
C
N
H
HS
SH
HO
PPh3
4a
N-carboxyl-p-methoxyphenylsulfonamide
Scheme 3. Proposed pathways for the formation of trans-4a.
served signals integrate well to the corresponding protons. The 13
C
NMR signals in the range d 201.35–209.39 ppm as compared to the
potassium salt of the ligands (d 197–198.5 ppm) are indicative of
M–S bonding in the complexes. In the 31P{1H} NMR spectra of
the heteroleptic complexes 3, 4, 4a, 5 and 6, the singlets at d
34.88, 31.04, 24.04, 29.87 and d 17.67 ppm (flanked by the plati-
num satellites, 1J(195Pt–31P) = 3125 Hz), respectively, are diagnostic
of PPh3 coordination in magnetically identical environments. Per-
sistence of the rare anagostic intramolecular C–Hꢀ ꢀ ꢀM interactions
in 4a and 5 as revealed by X-ray crystallography (vide infra) could
Table 1
Crystallographic data and structure refinement parameters of complexes.
Compound
1
2
4a
5
Empirical formula
Formula weight
Crystal system
Space group
T (K)
C
48H86N4NiO6S6
C64H54N2NiO6P2S6
1260.10
C36H32P2PdS2
697.08
PdC43H35P2S3O2N
862.30
orthorhombic
Pbca
1066.28
triclinic
P1
150(2)
triclinic
triclinic
ꢀ
ꢀ
ꢀ
P1
P1
150(2)
150(2)
150(2)
Crystal size (mm)
k (Å)
0.30 ꢃ 0.05 ꢃ 0.05
0.30 ꢃ 0.05 ꢃ 0.05
0.32 ꢃ 0.23 ꢃ 0.20
0.34 ꢃ 0.29 ꢃ 0.25
0.71073
0.71073
0.71073
0.71073
a (Å)
b (Å)
c (Å)
10.2054(8)
11.0022(10)
13.5452(11)
83.689(7)
9.0028(8)
9.160(3)
9.668(3)
10.191(4)
73.008(5)
16.4553(15)
18.3265(9)
25.3452(17)
90
13.0778(13)
13.3095(13)
73.923(9)
a
(°)
b (°)
80.022(7)
88.569(8)
88.240(6)
90
c
(°)
68.105(8)
1388.1(2), 1
1.276
70.467(9)
1415.1(2), 1
1.479
67.423(5)
793.6(5), 1
1.459
90
V (Å3), Z
7643.3(9), 8
1.952
Dcalc (Mg mꢂ1
)
Reflection collected
Data/restraints/parameter
Color, habit
7760
7898
5158
27099
7760/0/308
needle, green
574
0.622
0.854
7898/0/368
needle, green
660
0.677
1.016
3725/3/188
needle, yellow
356
0.841
1.146
8689/0/469
plate, yellow
4573
1.051
1.031
F(0 0 0)
l
(mmꢂ1
)
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0444, wR2 = 0.0898
R1 = 0.0806, wR2 = 0.0958
0.510 and ꢂ0.525
R1 = 0.0346, wR2 = 0.0881
R1 = 0.0468, wR2 = 0.0910
0.378 and ꢂ0.546
R1 = 0.0664, wR2 = 0.1717
R1 = 0.0940, wR2 = 0.2462
1.623 and ꢂ2.569
R1 = 0.0459, wR2 = 0.0960
R1 = 0.0703, wR2 = 0.1027
0.551 and ꢂ0.733
Largest difference peak and hole (e Åꢂ3
)

N. Singh et al. / Inorganica Chimica Acta 363 (2010) 3589–3596
3593
Fig. 3. ORTEP diagram of 4a with ellipsoid at 50% probability, together with the
atom numbering.
Fig. 1. ORTEP diagram of the [NiL2]2ꢂ anion and NBu4 cation in 1 with ellipsoids at
þ
50% probability, together with the atom numbering scheme.
Fig. 4. ORTEP diagram of 5 with ellipsoid at 50% probability, together with the atom
numbering.
Table 2
Selected bond length and bond angles of complexes 1 and 2.
Fig. 2. ORTEP diagram of the [NiL2]2ꢂ anion and PPh4 cation in 2 with ellipsoids at
þ
1
2
50% probability, together with the atom numbering scheme.
Bond length (Å)
Ni(1)–S(1)
Ni(1)–S(2)
S(1)–C(3)
2.2057(6)
2.1883(6)
1.728(2)
1.739(2)
1.305(2)
2.2034(5)
2.2091(5)
1.7334(2)
1.7341(2)
1.306(2)
ric demands of the PPh3 ligand and the (S,S) coordination of the li-
gand dithiocarbimate. The Pd–S(1) and Pd–S(2) bond lengths are
2.3057(9) and 2.3458(9) Å whereas Pd–P(1) and Pd–P(2) Å dis-
tances are 2.3134(9) Å and 2.3350(9) Å, respectively.
For 1, 2 and 5, the C–S and C@N bond lengths in the range 1.71–
1.74 Å and 1.29–1.30 Å show that the carbon–sulfur bonds are con-
S(2)–C(3)
C(3)–N(4)
N(4)–S(5)
S(5)–O(51)
S(5)–O(52)
1.6213(18)
1.4432(14)
1.4446(15)
1.6295(14)
1.4416(12)
1.4379(12)
Bond angles (°)
S(1)–Ni(1)–S(2)
S(1)–C(3)–S(2)
C(3)–S(1)–Ni(1)
C(3)–S(2)–Ni(1)
N(4)–C(3)–S(1)
N(4)–C(3)–S(2)
O(51)–S(5)–O(52)
O(51)–S(5)–N(4)
O(52)–S(5)–N(4)
78.64(2)
78.37(2)
siderably shorter than the C–S single bonds (ca. 1.815 Å) due to p-
106.87(11)
87.03(7)
107.05(9)
87.15(6)
delocalization over CS2 unit whereas the carbon–nitrogen bonds
are reasonably close to C@N double bond in the complexes. Meth-
oxy substitution on the phenylsulfonyl moiety elicits very small
changes in the bond dimensions.
The M–S, M–P, C–S and C@N bond lengths in 1, 2, 4a and 5 are
well in agreement with the previously reported dimensions for the
related dithio complexes [22–28].
87.32(7)
86.96(6)
131.67(16)
121.45(16)
116.37(9)
105.77(9)
112.49(9)
132.10(13)
120.84(13)
117.11(7)
105.20(7)
111.83(7)

3594
N. Singh et al. / Inorganica Chimica Acta 363 (2010) 3589–3596
Table 3
nounced upfield region as compared to uncoordinated group
whereas anagostic hydrogens show remarkably downfield shift of
the involved H atoms. These represent unique examples of anago-
stic interactions in mixed phosphine–dithioligand complexes.
These types of interactions are rarely observed but one example
has recently been reported [42] in the dithiolate complex [{Ni(L)2-
CuI}6] [L contains a 4-methylphenyl ring bonded to the dithioli-
gand] involving the phenyl ring proton of the dithioligand.
The large cations in 1 and 2 prevent any stacking of the anions
indeed there are no intermolecular Sꢀ ꢀ ꢀS distances less than 6 Å.
These result in somewhat lower conductivities of the complex salts
(vide infra) as compared to the extensive conjugation exhibited in
the analogous of maleonitriledithiolate (mnt2ꢂ) and 1,3-dithiole-2-
thione-4,5-dithiolate (dmit2ꢂ) complex salts.[1] In 5 the bulky PPh3
ligands in the coordination sphere also prevent stacking and there
is no intermolecular Sꢀ ꢀ ꢀS distance less than 7.5 Å.
Selected bond length and bond angles of complex 4a.
Bond length (Å)
Pd–S(1)
Pd–P(1)
2.294(7)
2.314(6)
Bond angles (°)
S(1)–Pd–P(1)
91.85(7)
Table 4
Selected bond length and bond angles of complex 5.
Pd–S(1)
Pd–S(2)
Pd–P(1)
Pd–P(2)
C(3)–N(4)
2.3057(9)
2.3498(9)
2.3134(9)
2.3349(9)
1.297(5)
C(3)–S(1)
C(3)–S(2)
S(5)–O(51)
S(5)–O(52)
1.736(4)
1.744(4)
1.429(3)
1.434(3)
Bond angles (°)
S(1)–Pd–S(2)
P(1)–Pd–P(2)
S(1)–Pd–P(1)
S(1)–Pd–P(2)
S(2)–Pd–P(1)
For compounds 3 and 6 the crystals were of lower quality and
the structures could not be refined successfully. However, cell
dimensions and preliminary refinements showed that both are
isomorphous with 5 crystallizing in the orthorhombic space group
Pbca. Cell dimensions are a = 16.354(3), b = 18.381(3), c =
75.11(3)
98.19(3)
91.39(3)
169.04(3)
165.15(4)
S(2)–Pd–P(2)
95.86(3)
117.6(2)
104.86(19)
111.82(18)
O(51)–S(5)–O(52)
O(51)–S(5)–N(4)
O(52)–S(5)–N(4)
25.287(4) Å, V = 7601(2) Å3, Z = 8 for
3 and a = 16.2469(7),
b = 18.222(9), c = 25.135(2) Å, V = 7438(6) Å3, Z = 8 for 6. No de-
tailed discussion on the geometric data can be presented on the ba-
sis of the data collected.
It is particularly interesting that packing effects together with
the steric and electronic impediments of both bulky ligands and
diamagnetic square planar Pd(II), d8 forces the ortho-proton on
one of the phenyl rings of a PPh3 ligand to be in close proximity
to one of the two vacant axial positions around the metal atom
thus creating unusual anagostic or preagostic binding interactions
[38–41], and these have been observed in both 4a C(20)–
H(20)ꢀ ꢀ ꢀPd: 2.8 Å; \C–H–Pd: 126° and 5 C(25)–H(25)ꢀ ꢀ ꢀPd: 2.7 Å;
\C–H–Pd: 125°. These interactions are illustrated in Fig. 5 and
show that the hydrogen atoms are in approximately axial positions
in the metal coordination spheres. The existence of anagostic inter-
actions in solution for these complexes could not be confirmed in
the 1H NMR spectra (vide supra). It is worth mentioning that the
anagostic and agostic C–Hꢀ ꢀ ꢀM interactions are characterized by
significantly different structural and spectroscopic characteristics.
Anagostic C–Hꢀ ꢀ ꢀM interactions are characterized by relatively
long Mꢀ ꢀ ꢀH distances (ꢁ2.3 to 2.9 Å) and large C–Hꢀ ꢀ ꢀM angles
(ꢁ110° to 170°) whereas agostic interactions are characterized by
relatively short M–H distances (ꢁ1.8 to 2.3 Å) and C–Hꢀ ꢀ ꢀM angles
usually in the range (ꢁ90° to 140°) [38–41]. Further, the chemical
shifts of agostic hydrogen atoms are typically observed at pro-
The crystal structures of 1, 2 and 5 are stabilized by intermo-
lecular hydrogen bond interactions of the type C–Hꢀ ꢀ ꢀS, C–Hꢀ ꢀ ꢀO
and C–Hꢀ ꢀ ꢀN) in Table S1 and Fig. S1 (see Supplementary mate-
rial). The packing of the complex anions in 1 and 2 is characterized
by one-dimensional sheet-like arrangements separated by sheets
þ
of isolated cations NBu4 or PPh4þ. In the anions 1 and 2 the non-
bonded intra-ligand S(1)ꢀ ꢀ ꢀS(2) separations are 2.784(1) and
2.788(1) Å and the inter-ligand S(1)ꢀ ꢀ ꢀS(2) distances are 3.399(1),
3.420(1), respectively. The S(1)–C(3)–N(4)–S(5) torsion angles
are 4.3(1), 1.1(1)° with S(1)ꢀ ꢀ ꢀS(5) distances of 3.293(1),
3.315(1) Å. Similar dimensions in 5 are S(1)ꢀ ꢀ ꢀS(2) 2.838(1) Å,
S(1)ꢀ ꢀ ꢀS(5) 3.357(1) Å with a torsion angle of 5.8(1)°. In all three
structures Sꢀ ꢀ ꢀS distances are significantly shorter than the sum
of the van der Waals radii (ca. 3.60 Å) of sulfur atoms in the mol-
ecule indicating substantial nonbonded intramolecular Sꢀ ꢀ ꢀS inter-
action. In the case of 4a, C–Hꢀ ꢀ ꢀ
p (Fig. S2 see Supplementary
material) and C–Hꢀ ꢀ ꢀS intermolecular noncovalent interactions
are present and cause a polymeric chain to be formed in the crys-
tal structure.
Fig. 5. View of the C–HꢀꢀꢀPd anagostic interactions in complex 4a (left) and 5 (right).

N. Singh et al. / Inorganica Chimica Acta 363 (2010) 3589–3596
3595
Fig. 6. Electronic absorption (1–6) and emission (5, 6) spectra in CH2Cl2.
3.4. Electronic absorption and emission spectra
3.5. Conductivity
The UV–Vis absorption spectra of all complexes obtained in
CH2Cl2 solution (Fig. 6) and solid in nujol (Fig. S3 in Supporting
material) are comparable thereby suggesting that the compounds
retain their structure in the solution. In all complexes the absorp-
Pressed pellet conductivity, rrt ꢁ10ꢂ5 S cmꢂ1 of the complex
salts 1 and 2 is somewhat low because of absence of Sꢀ ꢀ ꢀS/Mꢀ ꢀ ꢀS
intermolecular contacts (vide supra in the crystallographic section)
which is one of the important prerequisite for the higher conduc-
tivities of the complexes (Fig. 7). Despite the variation in the coun-
ter cations there is no perceptible enhancement in the conductivity
of these salts. Nevertheless, they exhibit semi-conductor behavior
as there is progressive increase in the conductivity with increase in
temperature which ideally decreases with decreasing temperature
in the 313–453 K regions with the band gap of 0.54 eV in 1 and
tions at 234–355 nm are assignable to
p–p
*, ILCT transitions. The
additional absorptions near 465 and 600 nm in solution as well
as nujoll mull in the nickel complexes (1, 2 and 3) are assigned
to Ni S, MLCT and d–d transitions for square planar geometry
about the metal center [6]. For the heteroleptic palladium and plat-
inum complexes the MLCT and d–d transitions are expected to oc-
cur at somewhat higher energies. The absorptions at about 430 nm
in 4 and 5 and at 358 in 6 are assigned to MLCT and ILCT [43] tran-
sitions, respectively, possibly with some admixture of metal d
orbitals.
0.57 eV in 2. The perceptible enhancement in
r with temperature
may be ascribed to the thermal activation of electrons. As expected
the heteroleptic complexes 3–6 show insulating behavior due to
the presence of bulky PPh3 ligands which hinder the stacking of
the molecules.
When excited at 295 nm, 5 shows a photoluminescent emission
at ꢁ360 nm (Fig. 6) which mainly originates from the
p–p
*, ILCT
transitions [43]. Upon excitation at 235 nm, 6 displays a photolu-
minescent emission at ꢁ375 nm accompanied with a medium
emission band at 325 nm arising from the ILCT transitions [43].
Complexes 1, 2, 3 and 4 are non-luminescent because the low spin
d8, nickel(II) and palladium(II) complexes are well known quench-
ers [44,45] due to the occurrence of low energy bands in the visible
region. It is important to note that the lone pairs of the phosphorus
4. Conclusions
New complex salts 1 and 2 and sterically congested heteroleptic
cis-complexes 3, 4, 5 and 6 and trans-4a have been synthesized and
fully characterized. The trans-complex was obtained as a result of
ligand PPh3 induced catalytic transformation during the course of
the preparation of 4. The presence of rare anagostic C–Hꢀ ꢀ ꢀPd inter-
actions is detected by the single crystal X-ray analyses in 4a and 5.
The palladium and platinum complexes display photolumines-
cence properties in solution at room temperature. The low rrt va-
lue ꢁ10ꢂ5 S cmꢂ1 for 1 and 2 is due to the absence of Sꢀ ꢀ ꢀS/Mꢀ ꢀ ꢀS
intermolecular contacts which was identified by X-ray crystallog-
raphy. The complex salts show semi-conductor behavior in the
temperature range 313–453 K. The heteroleptic complexes (3–6)
are insulators.
atoms are not involved in p-conjugation to the same extent as the
nitrogen lone pairs [44–46] As a result upon coordination to metal
centers phosphine ligands generally do not show larger wave-
length shifts in the photoluminescence emission [46].
-3.5
-3.7
-3.9
-4.1
-4.3
-4.5
-4.7
1
2
Acknowledgement
We gratefully acknowledge the Council of Scientific and Indus-
trial Research (CSIR), New Delhi for funding (Project No. 01(2290)/
09/EMR-II) and Dr. A. Mishra, for fluorescence spectra. We thank
the Department of Chemistry, Banaras Hindu University, EPSRC
(UK) and the University of Reading for funds for the X-Calibur
CCD diffractometer.
2.1
2.3
2.5
2.7
2.9
3.1
3.3
Appendix A. Supplementary material
1 / T X 1000 (K-1)
CCDC 757823, 757824, 772495 and 772496 contain the supple-
Fig. 7. Temperature dependent electrical conductivities of 1 and 2.
mentary crystallographic data for 1, 2, 4a and 5. These data can be

3596
N. Singh et al. / Inorganica Chimica Acta 363 (2010) 3589–3596
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