Syntheses, crystal structures and properties of sterically congested heteroleptic complexes of group 10 metal ions with p-tolylsulfonyl dithiocarbimate and 1,2-bis (diphenylphosphino) ethane

Article abstract of DOI:10.1016/j.inoche.2010.08.014

Three novel heteroleptic complexes of the type cis- [ML(dppe)] [M = Ni(II), Pd(II), Pt(II); L = p-tolylsulfonyl dithiocarbimate; dppe = 1,2-bis(diphenylphosphino)ethane] have been prepared and characterized. X-ray crystallography revealed the close proximity of one of the ortho phenyl protons of the dppe ligand to the metal in the Ni(II) complex showing existence of the less common C-H?Ni anagostic interactions observed for the first time in the dithio-phosphine mixed-ligand systems. The platinum complex showed a strong photoluminescence emission near visible region in CH₂Cl₂ solution.

Full text of DOI:10.1016/j.inoche.2010.08.014

Inorganic Chemistry Communications 13 (2010) 1451–1454
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Syntheses, crystal structures and properties of sterically congested heteroleptic
complexes of group 10 metal ions with p-tolylsulfonyl dithiocarbimate and
1,2-bis (diphenylphosphino) ethane
Nanhai Singh a, , Bandana Singh a,1, Santosh K. Singh a,1, Michael G.B. Drew b
⁎
a
Department of Chemistry, Banaras Hindu University, Varanasi-221005, U.P., India
Department of Chemistry, University of Reading, Whiteknights, Reading RG6 6AD, UK
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 July 2010
Accepted 10 August 2010
Available online 14 August 2010
Three novel heteroleptic complexes of the type cis- [ML(dppe)] [M = Ni(II), Pd(II), Pt(II); L = p-tolylsulfonyl
dithiocarbimate; dppe = 1,2-bis(diphenylphosphino)ethane] have been prepared and characterized. X-ray
crystallography revealed the close proximity of one of the ortho phenyl protons of the dppe ligand to the
metal in the Ni(II) complex showing existence of the less common C–H⋯Ni anagostic interactions observed
for the first time in the dithio-phosphine mixed-ligand systems. The platinum complex showed a strong
photoluminescence emission near visible region in CH2Cl2 solution.
Keywords:
Dithiocarbimate
dppe
© 2010 Elsevier B.V. All rights reserved.
Heteroleptic
Fluorescence
Anagostic interaction
Group 10 metal complexes of dianionic dithiocarbimates are
of current interest because of their resemblance to unianionic
dithiocarbamates and related dianionic dithioligands such as iso-
maleonitrile dithiolate (i-mnt2−), maleonitriledithiolate (mnt2−) and
1,3-dithiole-2-thione-4,5-dithiolate (dmit2−) which have exhibited
interesting physical and spectroscopic properties [1–9]. The impor-
tance of ternary complexes of platinum(II) with dithioligands
containing polypyridyl and less often phosphine ligands as lumines-
cent materials and photocatalysts has been known for some time [10–
12]. The phosphine ligands because of their σ-donor and π-acceptor
properties, larger steric demands, electronic and energetic factors
have been useful components in the metal complexes which provide
interesting chemical reactivity and physical properties, such as the
conversion of light to chemical energy, and acting as chemical sensors
and probes in biological imaging [10,13–16]. Therefore, the synthesis,
structure and luminescent properties of the analogous complexes
with a chelating phosphine–dithioligand combination are a worthy
subject for active investigation.
it may exhibit greater electron delocalization through C–S, C–N and
N–SO2–Ar bonds and (ii) upon S, S coordination to a metal center it
forms a more strained four-membered chelate ring in comparison
with the five-membered ring formed with the mnt2− complexes
which in turn can influence intra and inter ligand S⋯S and M⋯S
dimensions. These features make huge differences in the structures
and properties of their complexes.
In this communication we report the syntheses, structures and
photoluminescent properties of three novel sterically crowded hetero-
leptic complexes of the form cis-M(dppe)L [M = Ni(II), Pd(II), Pt(II);
L = p-tolylsulfonyl dithiocarbimate (p-CH3C6H4SO2N = CS22−), dppe =
1,2-bis(diphenylphosphino)ethane].
The heteroleptic complexes M(dppe)L were obtained in similar
conditions by the reaction of NiCl2·6H2O or K2[MCl4] [M = Pd(II), Pt
(II)] with the ligand L, and dppe, (one equivalent of each) in CH3OH/
CH2Cl2 according to Scheme 1.
In the IR spectra all the three complexes display absorptions near
1435, 1216–1292, 1120 and 900 cm−1 characteristic of υ(C=N),
Compared to the rich coordination chemistry of the dithiocarba-
mate ligand, studies of those with the dithiocarbimate ligands are
extremely limited [17–19]. Complexes of the ligand aromaticsulfonyl
dithiocarbimate and their possible applications have however been
exploited recently [20–22]. This ligand has two important features (i)
υasym(SO2), υsym(SO2) and υasym(CS2) vibrations respectively indi-
cating S, S coordination of the ligand dithiocarbimate with
increasing importance of the canonical form I (Scheme S1 in the
ESI) [20–22].
Apart from the characteristic 1H and 13C NMR signals, the 31P
spectrum of 1 displays a singlet at δ 58.1 ppm whereas 2 and 3 show
two singlets at δ 52.6 and δ 4.4 ppm and δ 42.1 ppm flanked with
platinum satellites with 1J (195Pt–31P)=2983 Hz and δ 4.4 ppm
respectively due to P, P coordination mode of the ligand dppe; the
signal at δ 4.4 ppm shows more complex solution behavior of 2 and 3.
⁎
Corresponding author. Fax: +91 542 2368127.
E-mail addresses: nsingh@bhu.ac.in, nanhai_singh@yahoo.com (N. Singh).
Fax: +91 542 2368127.
1
1387-7003/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2010.08.014

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N. Singh et al. / Inorganic Chemistry Communications 13 (2010) 1451–1454
Scheme 1. Synthesis of Complexes.
A perceptible lowfield shift observed for the palladium and platinum
complexes indicates the greater strengths of Pt–P and Pd–P bonds
compared to Ni–P bonds. The expected downfield shift in the phenyl
proton of the dppe ligand involved in the C–H⋯Ni rare anagostic
interactions as revealed by X-ray crystallography (vide infra) could
not be detected because of the presence of the phenyl proton signals
of the ligand p-tolylsulfonyl dithiocarbimate in the same region.
Hence, the persistence of the anagostic interactions in solution cannot
be unequivocally confirmed.
The immediate coordination geometry about the metal atom in
Ni(dppe)L 1, Pd(dppe)L 2 and Pt(dppe)L 3 are defined by the two
phosphorus atoms of dppe and the two sulfur atoms S(1) and S(2) of L
in which the metal atom lies at the center of a distorted square planar
coordination geometry [23] (Figs. 1, 2 and S1 in the ESI). The bond
lengths and angles are listed in Table 1. In 1, the P(1)–Ni–S(1) angle at
98.57(7)° is more distorted from ideal than the P(2)–Ni–S(2) angle at
95.47(7)° but in 2 and 3 the reverse is the case with P(1)–M–S(1)
angles of 94.98(2) and 95.24(6)° and P(2)–M–S(2) angles of 103.82
(2) and 103.47(6)°. The P(1)–M–P(2) angles, part of a five-membered
chelate ring are as expected much closer to the ideal 90° [87.01(6),
85.75(2), and 86.17(6)°] than the S(1)–M–S(2) angles part of a four-
membered chelate ring [79.19(6), 75.42(2), and 75.11(6)°] in the
three complexes 1, 2 and 3 respectively. The root mean square (r.m.s.)
deviations of M, S(1), S(2), P(1) and P(2) from the least square planes
are 0.0656, 0.0424, and 0.046 Å in 1, 2 and 3 respectively, thus
showing very little deviation from planarity. The M–S(1) and M–S(2)
distances 2.1836(15) and 2.2040(16) Å differ significantly in 1, but are
more similar in 2 and 3 at 2.3229(5); 2.3379(6) Å and 2.3395(18);
2.3454(18) Å respectively. On the contrary, no significant differences
are observed in the M–P(1) and M–P(2) distances of 2.1684(16);
2.1728(15) Å in 1. M–P distances in 2 at 2.2567(5); 2.2803(5) Å and 3
at 2.2433(17); 2.2585(18) Å also show barely significant differences.
Another feature showing the difference between 1 on one hand and 2
and 3 on the other is the trans angles. In 1, the P(2)–Ni–S(1) and P(1)–
Ni–S(2) angles are similar at 173.95(7) and 174.43(8)° while in 2 and
3 the former angle at 179.22(2) and 178.59(2)° is far larger than the
latter at 169.42(2) and 169.30(2). As will be discussed later the
difference can be related to the Ni⋯H interactions. In all three
structures the S(1)–C(1)–N(1)–S(3) torsion angles are close to zero
(−1.6(8), 4.3(4), and 3.0(10)°) showing significant planarity. The
average C–S and C–N bond lengths in 1, 2 and 3 respectively are well
in the range of carbon–sulfur single bond and carbon–nitrogen double
bond length in [20–22] accordance with the importance of the
resonance form I in the complexes (Scheme 1 in the ESI). A
comparison of the structural data shows the trend NibPdbPt for M–
S and NibPdNPt for M–P bond distances. The bite angles S(1)–M–S(2)
and P(1)–M–P(2) are observed in the order NiNPdNPt. As expected the
Fig. 1. ORTEP diagram of 1 with 30% probability, together with the atom numbering.
Table 1
Selected bond lengths [Ǻ] and angles [°] in complexes 1, 2 and 3.
1
2
3
Bond lengths/Å
M–S(1)
M–S(2)
M–P(1)
M–P(2)
C(1)–S(1)
C(1)–S(2)
C(1)–N(1)
2.1837(16)
2.2043(16)
2.1680(16)
2.1728(16)
1.734(5)
2.3229(6)
2.3377(6)
2.2568(6)
2.2803(6)
1.731(2)
1.747(2)
1.292(3)
2.3375(18)
2.3465(18)
2.2437(17)
2.2564(18)
1.769(6)
1.735(6)
1.305(6)
1.740(8)
1.262(9)
Bond angles/°
S(1)–M–S(2)
P(1)–M–P(2)
P(2)–M–S(2)
P(1)–M–S(1)
P(2)–M–S(1)
P(1)–M–S(2)
79.19(6)
87.01(6)
95.47(7)
98.57(7)
173.95(7)
174.43(8)
75.42(2)
85.75(2)
103.82(2)
94.98(2)
179.22(2)
169.42(2)
75.11(6)
86.17(6)
103.47(6)
95.24(6)
178.59(6)
169.30(6)
Fig. 2. ORTEP diagram of 2 with 30% probability, together with the atom numbering.

N. Singh et al. / Inorganic Chemistry Communications 13 (2010) 1451–1454
1453
radii. The significant interaction parameters along with the van der
Waals radii are listed in Table S1 in the ESI.
The occurrence of some common multiple absorptions (Fig. 4) in
⁎
the range 246–400 nm are mainly the ligand centered π–π , ILCT
transitions [12,27]. In the case of the nickel complex the weak broad
absorptions at 428 and 493 nm assignable to Ni←S, MLCT and d–d
transitions respectively are consistent with square planar geometry
[12,19,20] about the metal center. For palladium and platinum
complexes these absorptions are expected to appear at relatively
higher energies which are probably obscured by the ILCT transitions.
Unlike 1 and 2, which show weak luminescence emissions (Fig. 4)
near 350 nm upon excitation at 313 and 237 nm respectively, the
platinum complex 3, when excited at 260 nm, displays a strong
emission at 375 nm which arises from the ILCT transitions [12]. It is
worth mentioning that the lone pairs of the phosphorus atom are not
involved in the π-conjugation as compared to the nitrogen lone pairs
[28,29]. Thus upon coordination to metal centers the phosphine
ligands do not cause remarkable spectral wavelength shifts in the
photoluminescence emissions [29].
Fig. 3. View of the C–H⋯Ni anagostic interactions in complex 1.
In conclusion three new heteroleptic complexes Ni(L)(dppe) 1,
Pd(L)(dppe) 2 and Pt(L)(dppe) 3 [L = p-tolylsulfonyl dithiocarbi-
mate] have been prepared and fully characterized. All three structures
show intramolecular M⋯H interactions but that on 1 is the strongest.
Complex 1 is a rare example with MP2S2 coordination sphere having
the anagostic interaction. The platinum complex 3 showed intense
photoluminescence emission near visible region in solution.
Supplementary materials related to this article can be found online
at doi:10.1016/j.inoche.2010.08.014.
differences between nickel and palladium complexes are greater than
those between palladium and platinum complexes.
As a result of packing effects together with the steric and electronic
restrictions of both bulky ligands and the d8 electronic configuration,
one of the phenyl groups on the atom P(1) in 1 is tilted more towards
the P(1) and S(1) atoms (P(1)–C–C angle 106.96°) as compared to
atom P(2) towards P(2) and S(2) atoms (P(2)–C–C angle 107.16°)
facilitating rare intramolecular C–H⋯Ni anagostic or preagostic
interaction [24,25] via an ortho phenyl proton of the ligand dppe
(H⋯Ni distance 2.76 Å and C–H⋯Ni angle 121.25°) (Fig. 3). The
hydrogen is in an approximately axial position to the metal. Similar
but rather less pronounced C–H⋯M interactions with distances H(20)
⋯Pd 2.95 Å and H(20)⋯Pt 2.99 Å are also apparent in the palladium(II)
and platinum(II) complexes. Thus all three structures show M⋯H
interaction but that on 1 is the strongest [24,25]. As far as we are
aware, except for the heteronuclear cluster, [{Ni(L)2}2(CuI)6] [L =
dithiolate] where the ortho protons of the phenyl rings of the
dithioligand are involved in the less common anagostic interactions
[26], 1 is the first example showing this type of interactions in a
mixed-ligand dppe–dithioligand complex.
Acknowledgements
We acknowledge the CSIR, New Delhi for funding (Project No. 01
(2290)/09/EMR-II, New Delhi) and Dr. A. K. Mishra, Department of
Chemistry, B.H.U. for fluorescence spectra.
Appendix A. Supplementary material
The resonating structure of ligand together with details of the
syntheses, characterization data, figures and tables of the crystal
structures are provided. CCDC reference numbers 757820, 757821 and
757822 contain the supplementary crystallographic data for 1, 2 and 3.
These data can be obtained free of charge via http://www.ccdc.cam.ac.
uk/conts/retrieving.html.
Complexes 2 and 3 display weak intermolecular C–H⋯π centroid
interactions (Fig. S2 in the ESI). Also, in all three complexes distances
involving C–H⋯S, C–H⋯O and C–H⋯N intermolecular interactions (Figs.
S3 and S4 in the ESI) are smaller than the sum of the van der Waals
Fig. 4. Electronic absorption and fluorescence spectra of 1, 2 and 3.

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N. Singh et al. / Inorganic Chemistry Communications 13 (2010) 1451–1454
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