Unprecedented coordination of dithiocarbimate in multinuclear and heteroleptic complexes

Article abstract of DOI:10.1039/c0dt00582g

An uncommon coordination protocol induced by the p-tolylsulfonyl dithiocarbimate ligand (L) [L = p-CH₃C₆H ₄SO₂NCS₂^2-] in conjunction with PPh₃ allowed the formation of novel homodimetallic, Cu ₂(PPh₃)₄L (1), trinuclear heterometallic Cu₂Ni(L)₂(PPh₃)₄ (2) and heteroleptic complexes of general formula cis-[M(PPh₃)₂L] [M = Pd(ii) (3), Pt(ii) (4)]. The complexes have been characterized by microanalysis, mass spectrometry, IR, ¹H, ¹³C and ³¹P NMR and electronic absorption spectra and single-crystal X-ray crystallography. 2 uniquely consists of square planar, trigonal planar and tetrahedral coordination spheres within the same molecule. In both heteroleptic complexes 3 and 4 the orientation of aromatic protons of PPh₃ ligand towards the Pd(ii) and Pt(ii) center reveals C-H...Pd and C-H...Pt rare intramolecular anagostic or preagostic interactions. These complexes exhibit photoluminescent properties in solution at room temperature arising mainly from intraligand charge transfer (ILCT) transitions. The assignment of electronic absorption bands has been corroborated by time dependent density functional theory (TD-DFT) calculations. Complexes 1 and 2 with σ_rt values ～ 10^-6 S cm^-1 show semi-conductor properties in the temperature range 313-403 K whereas 3 and 4 exhibit insulating behaviour.

Full text of DOI:10.1039/c0dt00582g

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PAPER
Unprecedented coordination of dithiocarbimate in multinuclear and
heteroleptic complexes†
Bandana Singh,a Michael G. B. Drew,‡b Gabriele Kociok-Kohn,c Kieran C. Molloy‡c and Nanhai Singh*§a
Received 1st June 2010, Accepted 14th October 2010
DOI: 10.1039/c0dt00582g
An uncommon coordination protocol induced by the p-tolylsulfonyl dithiocarbimate ligand (L) [L =
p-CH3C6H4SO2N CS22-] in conjunction with PPh3 allowed the formation of novel homodimetallic,
Cu2(PPh3)4L (1), trinuclear heterometallic Cu2Ni(L)2(PPh3)4 (2) and heteroleptic complexes of general
formula cis-[M(PPh3)2L] [M = Pd(II) (3), Pt(II) (4)]. The complexes have been characterized by
microanalysis, mass spectrometry, IR, 1H, 13C and 31P NMR and electronic absorption spectra and
single-crystal X-ray crystallography. 2 uniquely consists of square planar, trigonal planar and
tetrahedral coordination spheres within the same molecule. In both heteroleptic complexes 3 and 4 the
orientation of aromatic protons of PPh3 ligand towards the Pd(II) and Pt(II) center reveals C–H ◊ ◊ ◊ Pd
and C–H ◊ ◊ ◊ Pt rare intramolecular anagostic or preagostic interactions. These complexes exhibit
photoluminescent properties in solution at room temperature arising mainly from intraligand charge
transfer (ILCT) transitions. The assignment of electronic absorption bands has been corroborated by
time dependent density functional theory (TD-DFT) calculations. Complexes 1 and 2 with srt values ~
10-6 S cm-1 show semi-conductor properties in the temperature range 313–403 K whereas 3 and 4
exhibit insulating behaviour.
electrochemical responses, luminescent based sensors, biological
Introduction
imaging probes and catalytic activities.1–3 The dianionic dithio-
The coordination chemistry of transition metal complexes with
carbimates are virtually akin to dithiocarbamates, except for a
dithioligands represents a very active area of research because of
variation in anionic charge. To the best of our knowledge the
their exciting conducting, magnetic, photophysical, properties and
multi-metallic complexes of the aromatic sulfonyldithiocarbimate
industrial applications.1 The majority of studies on the homo- and
ligands are still unexplored. Furthermore, this ligand has three
heterometallic complexes of 1,1- and 1,2-dithioligands including
important features (i) it shows greater electron delocalization
dithiocarbimates showed that coordination to metals usually oc-
beyond the MS2 bonds through the C–S, C N bonds and
curred solely through thiolate sulfur atoms with the nitrogen rarely
aromatic SO2 group (ii) it possesses multiple coordination sites
bonded, leaving the remaining donor atoms uncoordinated.1,2 The
such as (S,S), N and O atoms and (iii) it is similar in some
construction of mono- and multi-metallic Cu(I), Ni(II), Pd(II)
respects to both monoanionic dithiocarbamate and dianionic 1,1-
and Pt(II) complexes that support metal fragments in distinct
coordination environments achieved by multifunctional ligands
dithioligands such as i-mnt2- (i-mnt2- = isomaleonitriledithiolate)
which places it as intermediate between these two types of
and sterically demanding phosphines as ancillary ligands have
ligand, which make huge differences in the structure, binding and
received much attention owing to their significant luminescence
properties of its complexes.
properties with possible applications in solar energy conversion,
Surprisingly, despite their synthetic versatility and practical
utility as compared to the dithiocarbamates and related dithio
aDepartment of Chemistry, Faculty of Science, Banaras Hindu University,
Varanasi, 221005, India. E-mail: nsingh@bhu.ac.in; Fax: +91 542 2368127;
Tel: +91 542 2307321*108
ligand complexes, complexes with dithiocarbimates have gained
less attention.2 Recently, the coordination chemistry and possible
applications of transition metal aromatic sulfonyl dithiocarbimate
complexes have been exploited.4,5 Inspired by these observations
and considering the steric and energetic restrictions caused by the
ligand triphenylphosphine and aromatic sulfonyldithiocarbimate,
we have studied the unusual coordinative abilities of the dithiocar-
bimates in the organization of new multi-metallic and heteroleptic
complexes of Cu(I), Ni(II), Pd(II) and Pt(II) and their photolumi-
nescent and conducting properties and report the results here.
bDepartment of Chemistry, University of Reading, Whiteknights, Reading,
UK RG6 6AD
cDepartment of Chemistry, University of Bath, Bath, UK BA2 7AY
† Electronic supplementary information (ESI) available: Molecular pack-
ing and weak interaction diagrams. CCDC reference numbers 745652 (1),
745653(2), 745654 (3) and 745655 (4). For ESI and crystallographic data
in CIF or other electronic format see DOI: 10.1039/c0dt00582g
‡ For crystallographic correspondence.
§ For general correspondence.
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The absorptions below 400 cm-1 are assigned to u(M–S) vibrations
Results and discussion
in the complexes.
1
All the complexes display H and 13C NMR signals charac-
General aspects
teristic of the functional groups of the coordinated ligands and
integrate well to the corresponding hydrogens. The anticipated
downfield shift in the 1H NMR spectra for the ortho-proton of the
phenyl groups of the ligand PPh3 involved in the intramolecular
C–H ◊ ◊ ◊ M [Pd(II), Pt(II)] anagostic or preagostic interactions as
revealed by X- ray crystallography (vide supra) could not be
confirmed unambiguously as being retained in solution because of
the overlapping of observed aromatic signals of the p-tolylsulfonyl
dithiocarbimate ligand in the same region. However, upon cooling
the samples down to -60 ◦C in CDCl3, the resonances in the range
d 7.22–7.36 ppm begin to merge and eventually two to three broad
peaks are observed which may in part, be attributed to the presence
of weak anagostic interactions in solution. A noticeable shift of
d 10–13 ppm for the NCS2 carbon in the 13C NMR spectra of all
complexes compared to the uncoordinated dithiocarbimate ligand
indicates M–S bonding in the complexes. The 31P NMR spectrum
of 1 in CDCl3 displays a single resonance at d -1.29 ppm due
to the fluxional behaviour of the ligand PPh3 which causes signal
overlap at room temperature. On cooling the sample down to 0 ◦C
it shows two distinct signals at d -1.13 and 5.28 ppm associated
with the Cu(1) and Cu(2) centers, respectively. On further cooling
up to -60 ◦C the signal at d -1.13 ppm starts broadening and splits
into two broad peaks at d -0.04 and -0.88 ppm corresponding to
two PPh3 ligands because of the change in the environment i.e. N,S
coordination of dithiocarbimate ligand about the Cu(1) center. A
single strong peak observed at d 9 ppm is due to identical S,S
coordination of the dithiocarbimate about the Cu(2) center. The
compound, 2 displays three distinct 31P NMR signals at d 21.57,
4.61 and -0.11 ppm due to the square planar nickel(II), tetrahedral
copper(I) and trigonal planar copper(I) centers, respectively, thus
The homodimetallic complex Cu2(PPh3)4L (1) was prepared
by treating a methanolic solution of the ligand K2L and
dichloromethane solution of Cu(PPh3)2NO3 in 1 : 2 molar ratio.
Attempts to synthesise the trinuclear heterometallic complexes
Cu2M(L)2(PPh3)4 [M = Ni(II), Pd(II), Pt(II)] by treating two
equivalent of CH2Cl2 solution of Cu(PPh3)2NO3 with an in situ
generated aqueous solution of K2[M(L)2] [M = Ni(II), Pd(II), Pt(II)]
were only successful for M = Ni(II) 2. With M = Pd(II) 3 and Pt(II)
4 are formed due to PPh3 ligand transfer from Cu(PPh3)2NO3
to palladium(II) or platinum(II) meeting the steric and geometric
requirements of the system. Alternatively, 3 and 4 could also be
prepared by the reaction of an aqueous-methanolic solution of
K2MCl4 with K2L and the ligand PPh3 in appropriate molar ratio
(Scheme 1).
1
showing that the structure is retained in solution. In the 31P { H}
Scheme 1 Synthesis of the complexes.
NMR spectra of complex 3 a single resonance at d 30.94 ppm and
in 4 a well defined sharp singlet at d18.97 ppm flanked by 195Pt
satellites [J(195Pt–31P) = 3112.10 Hz] are in the range of analogous
dithiocomplexes.2g An appreciable low-field shift observed for the
palladium complex suggests greater strength of the Pt–P bond
compared to Pd–P bonds.
All four complexes are air stable solids and melt with decom-
position in the temperature range of 114–195 ◦C. They have been
1
characterized by mass spectrometry, IR, UV-vis, H, 13C and 31P
NMR and single crystal X-ray analyses and their solid phase
conducting and solution photoluminescence properties studied.
The electronic absorption bands have been assigned by employing
time dependent density functional theory.
Crystal structure
Single crystals of complexes 1 and 2 were obtained by slow
diffusion of CH3OH in CH2Cl2 and ether in CH2Cl2 solution,
respectively, those of 3 and 4 were grown by slow evaporation
of CH2Cl2 : CH3CN solvent. The crystallographic details are
provided in Table 1. The structures of 1, 2, 3 and 4 are presented
in Fig. 1–4 and selected bond distances and angles are listed in
Tables 2, 3 and 4.
The structure of 1 contains the Cu2(PPh3)4L complex together
with five solvent methanol molecules (Fig. 1). Cu2(PPh3)4L is a
dinuclear complex in which ligand L, p-tolylsulfonyl dithiocarbi-
mate, acts as a bridging ligand between two Cu(PPh3)2 units. Both
copper atoms have distorted tetrahedral environments, Cu(2) is
bonded to two triphenylphosphine ligands and both sulfur atoms
of the ligand, (p-CH3C6H4SO2N CS2) in a chelating manner. The
nitrogen atom N(1) of the ligand and one of the chelating sulfur
atoms, S(2) is linked to the second metal Cu(1) the latter atom
Spectroscopy
In the ESI-MS spectra, the intense peaks at m/z 875.8 and 965
for 3 and 4 are consistent with the expected molecular ion peaks
at 876.33 and 964.99 respectively. The IR spectra of compounds
4,5
1–4 show diagnostic absorptions
near 1384–1473, 1300, 1145
and 990 cm-1 arising from u(C N), uasym(SO2), usym(SO2), and
asym(CS2) modes, respectively; the appearance of u(C N) at
u
higher stretching frequency compared to the free ligand L is
consistent with the domination of the resonance form I (Scheme 2).
Scheme
2
Resonance structures of the ligand p-tolylsulfonyl
dithiocarbimate.
624 | Dalton Trans., 2011, 40, 623–631
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Table 1 Crystallographic data and structure refinements for complexes
Compound
1·5CH3OH
2·CH2Cl2
3
4
Empirical formula
Formula weight
T/K
C85H87Cu2NO7P4S3
1581.80
293(2)
Monoclinic
P21/c
0.23 ¥ 0.22 ¥ 0.18
19.785(2)
16.651(2)
24.213(3)
90
94.18(2)
90
7955.6(16), 4
1.321
51 499
19 704[0.0715]
1724
0.748
C91H80Cl6Cu2N2NiO4P4S6
1980.30
100(2)
PdC44H37NO2P2S3
876.27
150(2)
Orthorhombic
PtC44H37NO2P2S3
964.96
150(2)
Orthorhombic
Crystal system
Triclinic
¯
Space group
P1
Pbca
Pbca
Crystal size/mm
0.18 ¥ 0.12 ¥ 0.08
0.25 ¥ 0.25 ¥ 0.12
0.40 ¥ 0.15 ¥ 0.10
˚
a/A
13.144(5)
16.3447(2)
16.3309(10)
˚
b/A
13.801(5)
25.209(5)
85.998(5)
83.325(5)
81.990(5)
4491(3), 2
1.464
29 778
18.3512(2)
25.5480(3)
90
90
18.3563(2)
25.5226(2)
90
90
˚
c/A
a/◦
b/◦
g /◦
90
90
3
˚
V/A , Z
7662.99(15), 8
1.519
114 928
8754 [0.0919]
3584
0.771
7651.09(11), 8
1.675
117 355
8720 [0.0854]
3840
3.955
D
calcd/Mg M-3
Reflection collected
Independent reflections [Rint
F(000)
]
21 371[0.0441]
2032
1.118
m/mm-1
GOF on F2
1.072
1.092
1.020
1.031
Final indices [I > 2s(I)]
R1 = 0.0709, wR2 = 0.1691
R1 = 0.1319, wR2 = 0.2209
1.344 and -0.908
R1 = 0.0883, wR2 = 0.2294
R1 = 0.1531, wR2 = 0.3193
2.343 and -1.394
R1 = 0.0399, wR2 = 0.0952
R1 = 0.0685, wR2 = 0.1095
0.898 and -0.639
R1 = 0.0289, wR2 = 0.0601
R1 = 0.0521, wR2 = 0.0679
0.957 and -1.268
R indices (all data)
Largest diffraction peak and
-3
˚
hole/e A
◦
˚
Table 2 Selected bond lengths (A) and angles ( ) for 1
˚
Bond lengths/A
Cu(1)–N(1)
Cu(1)–S(2)
Cu(1)–P(1)
Cu(1)–P(2)
Cu(2)–S(1)
Cu(2)–S(2)
2.154(4)
Cu(2)–P(3)
Cu(2)–P(4)
C(8)–N(1)
C(8)–S(1)
C(8)–S(2)
2.244(12)
2.241(12)
1.346(5)
1.703(4)
1.718(5)
2.447(12)
2.239(13)
2.239(13)
2.389(12)
2.442(12)
Bond angles/◦
P(1)–Cu(1)–N(1)
P(2)–Cu(1)–N(1)
P(1)–Cu(1)–S(2)
P(2)–Cu(1)–S(2)
P(3)–Cu(2)–S(1)
P(3)–Cu(2)–S(2)
P(4)–Cu(2)–S(2)
P(4)–Cu(2)–S(1)
N(1)–Cu(1)–S(2)
118.50(11)
111.48(11)
110.63(4)
111.92(4)
111.33(5)
113.01(4)
108.06(4)
118.79(4)
67.27(10)
S(1)–Cu(2)–S(2)
P(1)–Cu(1)–P(2)
P(3)–Cu(2)–P(4)
S(3)–N(1)–Cu(1)
S(1)–C(8)–S(2)
O(1)–S(3)–O(2)
O(1)–S(3)–N(1)
O(2)–S(3)–N(1)
74.74(4)
123.36(5)
121.30(5)
136.2(2)
118.0(3)
116.8(2)
104.8(2)
111.8(2)
˚
˚
2.447(12) A than that to the chelating S(1) at 2.389(12) A. The
˚
Cu(1)–N(1) bond length at 2.154(4) A is as expected for a Cu(1)–
N bond.
The structure of 2 contains the complex Cu2NiL2(PPh3)4
together with
3 molecules of dichloromethane (Fig. 2).
Cu2NiL2(PPh3)4 contains one Ni(II) and two Cu(I) centers in
different coordination environments i.e. square planar for Ni(II),
tetrahedral for Cu(1), and the rare three-coordinate trigonal
planar for Cu(2). Here, one of the dithiocarbimates chelates
Cu(1) through S(1), S(2) and additionally bridges Ni(1) via its
free nitrogen donor N(2) and Cu(2) via the coordinated sulfur
S(1) while the other dithiocarbimate chelates Ni(1) via S(3), S(4)
and one of its chelated sulfur atoms, S(3) bridges Cu(2) overall
constructing a strained six-membered ring composed of nickel,
copper, carbon, nitrogen and two sulfur atoms. Thus, this unusual
heterometallic complex has one dithiocarbimate ligand acting as
Fig. 1 ORTEP diagram of 1 with thermal ellipsoids set to 30% probability
level. Solvent molecules and hydrogen atoms are omitted for clarity.
thus bridging Cu(1) and Cu(2). Two triphenylphosphine ligands
are also attached to Cu(1) to complete the tetrahedral coordination
˚
sphere. The Cu–P distances are in the range 2.239(13)–2.244(12) A.
The bond lengths to the bridging sulfur atom S(2) are longer at
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◦
˚
Table 3 Selected bond lengths (A) and angles ( ) in 2
˚
Bond lengths/A
Ni(1)–N(2)
Ni(1)–P(3)
Ni(1)–S(4)
Ni(1)–S(3)
Cu(1)–P(1)
Cu(1)–P(2)
Cu(1)–S(1)
Cu(1)–S(2)
Cu(2)–S(1)
1.959(5)
2.213(2)
2.174(2)
2.234(2)
2.256(2)
2.259(2)
2.430(19)
2.396(2)
2.219(2)
Cu(2)–S(3)
Cu(2)–P(4)
C(44)–N(2)
C(63)–N(1)
C(44)–S(1)
C(44)–S(2)
C(63)–S(3)
C(63)–S(4)
2.260(2)
2.204(2)
1.356(9)
1.275(9)
1.757(7)
1.691(7)
1.765(7)
1.748(8)
Fig. 2 ORTEP diagram of 2 with thermal ellipsoids set to 30% probability
level. Solvent molecules and hydrogen atoms are omitted for clarity.
Bond angles/◦
S(4)–Ni(1)–S(3)
S(4) –Ni(1)–P(3)
P(3)–Ni(1)–N(2)
S(3) –Ni(1)–N(2)
S(4)–Ni(1)–P(3)
S(3) –Ni(1)–P(3)
S(4)–Ni(1)–N(2)
S(2)–Cu(1)–S(1)
P(1)–Cu(1)–P(2)
P(2)–Cu(1)–S(2)
P(1)–Cu(1)–S(2)
78.34(8)
89.17(8)
97.6(2)
P(1)–Cu(1)–S(1)
P(2)–Cu(1)–S(1)
P(4)–Cu(2)–S(1)
P(4)–Cu(2)–S(3)
S(1)–Cu(2)–S(3)
O(1)–S(5)–O(2)
O(1)–S(5)–N(1)
O(2)–S(5)–N(1)
O(3)–S(6)–O(4)
O(3)–S(6)–N(2)
O(4)–S(6)–N(2)
115.29(7)
110.44(7)
119.05(8)
130.65(8)
110.08(7)
119.5(4)
113.1(3)
104.1(3)
119.3(3)
111.5(3)
101.6(3)
95.2(2)
89.17(8)
166.41(8)
172.5(2)
73.53(6)
124.51(7)
109.31(7)
112.36(8)
Fig. 3 ORTEP diagram of 3 with 30% probability, together with the atom
numbering scheme. Only one component of the disordered phenyl group
attached to P1 is also shown for clarity.
◦
˚
Table 4 Selected bond lengths (A) and angles ( ) in complex 3 and 4
Complex 3
Bond angles/◦
˚
Bond lengths/A
Pd–S(1)
Pd–S(2)
Pd–P(1)
Pd–P(2)
C(1)–N
C(1)–S(1)
C(1)–S(2)
S(3)–O(1)
S(3)–O(2)
2.306(8)
2.347(8)
2.309(8)
2.326(9)
1.298(4)
1.746(3)
1.747(3)
1.437(2)
1.439(2)
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)
S(2)–Pd–P(2)
O(1)–S(3)–O(2)
O(1)–S(3)–N
O(2)–S(3)–N
75.20(3)
97.88(3)
92.30(3)
168.85(3)
166.00(3)
95.13(3)
117.89(15)
104.62(14)
111.20(14)
Complex 4
Fig. 4 ORTEP diagram of 4 with 30% probability, together with the atom
numbering. Only one component of the disordered phenyl group attached
to P1 is also shown for clarity.
Bond angles/◦
˚
Bond lengths/A
Pt–S(1)
Pt–S(2)
Pt–P(1)
Pt–P(2)
2.321(9)
2.354(9)
2.283(9)
2.295(9)
1.301(4)
1.747(4)
1.751(4)
1.436(3)
1.439(3)
S(1)–Pt–S(2)
P(1)–Pt–P(2)
S(1)–Pt–P(1)
S(1)–Pt–P(2)
S(2)–Pt–P(1)
S(2)–Pt–P(2)
O(1)–S(3)–O(2)
O(1)–S(3)–N
O(2)–S(3)–N
74.85(3)
97.82(3)
92.90(3)
168.47(3)
166.35(3)
94.89(3)
117.98(17)
104.69(16)
111.03(16)
Cu(2) and Cu(1) shows an increased bond length when compared
˚
to the Cu–S bonds to the terminal sulfur, by 0.041 and 0.034 A,
C(1)–N
respectively. The nickel atom Ni(1) has a four-coordinate square
planar environment with bond lengths Ni(1)–N(2) 1.959(5), Ni(1)–
C(1)–S(1)
C(1)–S(2)
S(3)–O(1)
S(3)–O(2)
˚
P(3) 2.213(2), Ni(1)–S(3) 2.234(2), Ni(1)–S(4) 2.174(2) A. As in the
two copper coordination spheres, the bond to the bridging sulfur
˚
is longer than that to the terminal sulfur, here by 0.060 A. The
3
3
˚
m-(k N,S,S) and the other as m3-(k S,S). As far as we are aware these
variations in the ligating mode of the dithioligands and resulting
formation of the multi-metallic complexes are unique; indeed 2
is the first crystallographically established system in the area of
dithiolate chemistry featuring three distinct geometries. The bonds
around the trigonal planar Cu(2), namely Cu(2)–S(1) 2.219(2),
four donor atoms are planar with a r. m. s. deviation of 0.081 A
with the nickel atom 0.015(1) A from the plane. The intermetallic
˚
˚
Ni(1) ◊ ◊ ◊ Cu(2) distance of 2.879 A is shorter than the sum of
˚
the van der Waals radii of Cu and Ni atom i.e. 3.03 A. The
remaining coordination sites around the metal ions are occupied
by the triphenylphosphine ligand. The angles around the Cu(2) in
2 vary substantially (110.08(8)–130.65(8)◦) but their sum is close
to 360◦ (359.8◦). This places the copper atom in the plane of the
three donor atoms within experimental error. The main source of
distortion from the ideal geometries around the three metals arises
from the small bite of the dithiocarbimate.
˚
Cu(2)–S(3) 2.260(2), Cu(2)–P(4) 2.204(2) A are shorter than
those around the tetrahedral Cu(1), Cu(2)–P 2.256(2), 2.259(2) A,
Cu(1)–S(1) 2.430(2), Cu(1)–S(2) 2.396(2) A. The distances around
Cu(1) are equivalent to those found in 1 for Cu(2) which has an
equivalent environment. In 2 the bridging sulfur atom around both
˚
˚
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˚
The C–N bond distances 1.346(5) A for 1 and 1.356(9) and
show that the hydrogen atoms are directed towards approximately
vacant axial positions in the metal coordination spheres. It appears
that such interactions in these complexes are favored due to
the steric and electronic demands of the bulky ligand PPh3 and
p-tolylsulfonyl substituent of the dithiocarbimate moiety and the
d8 configuration of the metal ions. Such type of interactions
via ortho protons of the phenyl rings are unusual but have
been reported in a [Ni(L2)] [L = dithiolate] moiety present in
a heteronuclear cluster7 [{Ni(L)2}2(CuI)6]. To the best of our
knowledge this is the first example of anagostic interactions in
bis-triphenylphosphine metal dithiocarbimate complexes.
A closer inspection of the crystal structures of all com-
plexes reveals a number of weaker intermolecular non-covalent
C–H ◊ ◊ ◊ O, C–H ◊ ◊ ◊ S, C–H ◊ ◊ ◊ N and C–H ◊ ◊ ◊ Cl interactions (Ta-
ble S1 see ESI).† Molecular packing diagrams for 1 and 2 are given
in (Fig. S1 see ESI).† The lattice solvent molecules, methanol
in 1 and dichloromethane in 2, are located in cavities of 1 but
form a channel-like motif in 2 thus generating three dimensional
supramolecular networks.
˚
1.275(9) A for 2, respectively, clearly indicate that the former has
approximately the same length reported for the complex anion
[Ni(4-CH3C6H4SO2N CS2)2]2- whereas the C–N bond length
is intermediate between double and single bond lengths (1.27,
2c
˚
1.40 A) showing sufficient delocalization of p-electrons over
NCS2 unit. In 2 one of the C–N bond lengths is close to that
observed in complex 1 containing only Cu metal centres while
the other associated with the nickel center is well in the range
of C N double bond lengths observed2e in the neutral bis-
triphenylphosphine nickel(II) dithiocarbimate.
The structures of 3 and 4 are presented in Fig. 3 and 4,
respectively. For both complexes one of the phenyl ring carbon
atoms C(10), C(11), C(13) and C(14) of the PPh3 ligand are
disordered over two positions with an occupancy ratio of 51 : 49. In
both complexes, the central metal has a distorted square-planar
cis-MP2S2 coordination sphere. In 3 and 4, P(1)–M–S(1), P(2)–
M–S(2), P(1)–M–P(2) angles are all near 90◦, while the bite angle
S(1)–M–S(2) deviates somewhat [74.85(3)◦,75.20(3)◦, respectively,
atoms M, S(1), S(2), P(1) and P(2) are approximately planar show-
˚
ing a maximum deviation of 0.112 A. The M–P and M–S distances
Electronic absorption and photoluminescence spectra
in 3 and 4, respectively, are compatible with analogous Pt(II) and
Pd(II) dithiocomplexes.2g,h,4 In both 3 the Pd–S(1) and Pd–S(2)
The electronic absorption and emission spectra of all complexes
1–4 in CH2Cl2 solution are presented in Fig. 6.
˚
distances are similar at [2.306(8), 2.347(8) A] while in 4 the corre-
˚
sponding Pt–S distances are 2.321(9), 2.354(9) A similar to values
found in the reported4 anionic complex [Pt(C6H5SO2N CS2)2]2-.
The two M–P(1) and M–P(2) bond lengths are identical within
experimental error at 2.309(8), 2.326(9) for M Pd in 3 and
˚
˚
2.283(9), 2.295(9) A for M Pt in 4. The intraligand S ◊ ◊ ◊ S
˚
separations 2.840 A and 2.842 A in 3 and 4 respectively are
substantially shorter than the sum of the van der Waals radii of
˚
two sulfur atoms 3.60 A suggesting significant non-bonding S ◊ ◊ ◊ S
interaction.
˚
The C(1)–S(1,2) bond length [1.746(3)–1.751(4) A] are slightly
˚
shorter than the typical C–S single bond length (1.81 A) due to
Fig. 6 Electronic absorption of complexes 1–4 in CH2Cl2 solution at
room temperature.
the partial p-conjugation in the S–C–S group. The C(1)–N bond
length 1.298(4) A for 3 and 1.301(4) A for 4 exhibit significant
˚
˚
amounts of double bond character.
The most important feature in the crystal structures of 3 and
4 is that one phenyl group each from two different PPh3 in 4
and one phenyl group of one PPh3 ligand in 3 are oriented
such that the ortho proton of the phenyl rings are directed
The observed electronic absorption bands of 1, 3 and 4 have been
interpreted with the help of TD-DFT calculations. The electronic
absorption spectra of the complexes show some common bands
between 250–350 nm due to multiple ligand centered transitions.3,4
Calculations indicate that in 1 the lower energy band calculated at
349 nm with oscillator strength (f ) 0.0087 is due to the charge
transfer transition from sulfur atom coordinated to only one
copper center to the aromatic ring of the triphenylphosphine
group with some admixture of d-orbitals of both copper atoms
(Fig. 7). The next higher energy band at 305 nm having oscillator
strength (f ) 0.0421 is also attributed to ligand to ligand charge
transfer (LLCT) from the sulfur atom coordinated to both the
metal center to another aromatic ring of the triphenylphosphine
group (Fig. 7). The other transitions are also of the LLCT type.
Calculated excitation energies, wavelength, oscillator strength and
major contribution are given in Table 5.
˚
tow◦ards the metal(II) [3: C(16)–H(16) ◊ ◊ ◊ Pd 2.79 A; ∠C–H–Pd:
˚
124 ; 4: C(16)–H(16) ◊ ◊ ◊ Pt: 2.82; C(38)–H(38) ◊ ◊ ◊ Pt 2.89 A; ∠C–
H–Pt: 122, 123◦] resulting in unusual anagostic or preagostic
interactions.6 These interactions are illustrated in Fig. 5 and
Additionally, 2 exhibits a very weak band at 440 nm due to
Ni ← S (dithiocarbimate) MLCT transition; an absorption band
at 560 nm in the solid as Nujol mull (Fig. S2 see ESI)† of this
compound is ascribed to d-d transition for square planar geometry
about nickel(II).4
Fig. 5 View of the C–H ◊ ◊ ◊ Pd (left) and C–H ◊ ◊ ◊ Pt (right) anagostic
interactions in complex 3 and 4.
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Table 5 Calculated wavelength l/nm, excitation energies E/eV and
oscillator strength (f ) for 1, 3 and 4
Complex
l/nm
E/eV
f
Transition type
1
355
349
347
305
304
430
368
332
294
249
332
302
248
3.4890
3.5550
3.5779
4.0594
4.0744
2.8857
3.3714
3.7345
4.2188
4.9793
3.7345
4.1114
4.9932
0.0730
0.0087
0.0420
0.0421
0.0183
0.0026
0.0068
0.0200
0.1388
0.0125
0.0015
0.0225
0.0177
na → p*
na → p*
na → p*
na → p*
na → p*
n → P atom
n → p*
n → p*
LMCT
n → p*
n → p*
p → p*
p → p*
3
4
Fig. 8 Selected orbital transitions for palladium complex 3 (orbital
contour value is 0.05).
the dithiocarbimate ligand with slight intermingling of the metal
d-electrons to the aromatic ring of the triphenylphosphine. The rest
of the lower energy bands calculated at 302 and 248 nm having
oscillator strengths (f ) 0.225 and 0.0177, respectively, arise from
ligand to ligand (LLCT) and intraligand (ILCT) charge transfers
(Fig. 9). The calculated and observed bands are in good agreement
for both the complexes.
Fig. 7 Selected orbital transitions for the complex (orbital contour value
0.05).
The palladium complex 3 exhibits five bands at 419, 351, 325,
294 and 248 nm. TD-DFT calculations indicate that the low
energy band (calculated at 430 nm with oscillator strength (f )
0.0026) is due to HOMO → LUMO electron excitation and is
attributed to electron transfer from the coordinated sulfur atom
of the ligand to the phosphorus atom with slight intermixing of
the metal d-orbital (Fig. 8). The next two bands calculated at
368 nm and 332 nm with oscillator strengths (f ) 0.0068 and 0.0200,
respectively, are assigned to the charge transfer transitions from
the coordinated sulfur atoms and p-electron clouds of the aromatic
ring of the sulfonamide ring to the phosphorus and metal d-
orbital. Additionally, the absorptions calculated at 294 and 249 nm
with oscillator strengths (f ) 0.1338 and 0.0125, respectively, are
ascribed to ligand to-metal (LMCT) and intraligand (ILCT)
charge transfer transitions (Fig. 8).
Fig. 9 Selected orbital transitions for platinum complex 4 (orbital
contour value is 0.05).
When excited at 262 nm, 1 shows luminescence emission at
around 475 nm whereas upon excitation at 250 nm the emission
intensity of 2 is significantly decreased. In the light of previous
reports on the copper(I) phosphine complexes the emissive states
for the observed emissions may be ascribed principally to the
perturbed ligand centered p–p* transitions together with some
admixture of copper d-orbitals.3 The decrease in the luminescence
intensity of 2 is due to the presence of a nickel(II) centre, d8
electronic configuration which exhibits low energy absorptions
in the visible region and acts as a quencher. Upon excitation at
242 and 298 nm, 3 shows an intense emission band at 360 nm
which arises from intraligand (ILCT) and ligand to metal (MLCT)
charge transfer transitions. Likewise upon excitation at 235 and
302 nm, 4 displays a strong luminescent emission near visible
Likewise, in the case of platinum complex 4 the electronic
absorption spectrum recorded in CH2Cl2 solution displayed three
bands at 335, 296 and 248 nm. Quantum chemical calculations
reveal that the first lower energy band calculated at 332 nm with
oscillator strength (f ) 0.0015 can be assigned to the HOMO →
LUMO + 2 electron transfer from the coordinated sulfur atoms of
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1
region at 350 nm arising from the p → p* (ILCT) intraligand
characterized by IR, H and 13C NMR spectra. The precursor
Cu(PPh3)2NO3 was prepared by a method reported elsewhere.12
The melting point of the complexes were determined in an open
capillary using a Gallenkamps apparatus. Elemental analyses (C,
H, N, S) were performed on a Model CE–440 CHN analyzer. IR
transitions (Fig. 10).7,8
as KBr pellet and H, 13C and 31P NMR spectra in CDCl3 were
1
recorded on a Varian 3100 FTIR and JEOL AL 300 FTNMR
spectrophotometers respectively. Chemical shifts were reported
1
in parts per million using TMS as internal standard for H and
13C NMR and PCl3 as external standard (d 220 ppm) for 31P
NMR spectra. The electronic absorption and emission spectra
were obtained in CH2Cl2 solution at room temperature from Shi-
madzu UV–1700 Pharma Spec UV-Vis and Varian Cary Eclipse
Fluorescence spectrophotometers, respectively. Compressed pellet
electrical conductivities of the complexes were measured on a
Keithley 236 Source Measure Unit employing conventional two-
probe technique in the 313–403 K temperature range. The pellet
surfaces were coated with silver paint to make the electrical
contact. The electrospray ionization-mass spectra (ESI-MS) were
obtained in CH3OH on a Micromass Quattro II spectrometer.
Fig. 10 Fluorescence spectra of 1–4 in CH2Cl2 solution at room
temperature.
Upon coordination to a metal, the phosphine ligands do not
give rise to a dramatic spectral wavelength shift8 as compared to
nitrogen ligands because the phosphorus lone pairs are relatively
less involved in p- conjugation when compared to nitrogen lone
pairs.9,10
Conductivity
Synthesis of Cu2(PPh3)4L (1)
Pressed pellet conductivity, srt ~ 10-6 S cm-1 for both 1 and 2
(Fig. 11) shows their weakly conducting property because of the
very weak S ◊ ◊ ◊ S/M ◊ ◊ ◊ S intermolecular stacking. They exhibit
semiconductor behaviour as their conductivity progressively in-
creases with temperature and decreases ideally with temperature
in the range 403 K to 313 K with a band gap of 0.183–0.186 eV. The
heteroleptic complexes 3 and 4 show insulating behaviour because
of, the absence of S ◊ ◊ ◊ S/M ◊ ◊ ◊ S intermolecular stacking.
To a stirred 25 mL CH2Cl2 solution of Cu(PPh3)2(NO3) (1.3 g,
2 mmol) was added gradually 15 mL methanolic solution of the
ligand K2L·2H2O (0.360 g, 1 mmol). The yellow solid formed by
stirring the reaction mixture for about 4 h was filtered off and
washed with water followed by methanol and dried in vacuo over
CaCl2.
Yield: (1.04 g, 66%), m.p. 114–116◦ (dec.). Calcd for
C85H87Cu2NO7P4S3. C 64.54, H 5.54, N 0.89, S 6.08, Cu 8.03%.
Found: C 64.40, H 5.46, N 0.86, S 6.00, Cu 8.00%. IR (KBr, cm-1):
1384 n(C N), 1301 nasym (SO2), 1143 nsym(SO2), 995 nasym(CS2). 1H
NMR (300.40 MHz, CDCl3, ppm): d 7.47 (d, J = 9.0 Hz, 2 H, H2
and H6), 6.86 (d, J = 9.0 Hz, 2 H, H3 and H5), 2.33 (s, 3 H, CH3),
7.25 (m, 60 H, PPh3). 13C (75.45 MHz,, CDCl3, ppm): d 208.24
(N CS2), 142.76 (C4), 132.33 (C1), 132.02 (C3 and C5), 128.56
(C2 and C6), 21.46 (CH3). Triphenylphosphine signals: 133.93
(C1¢), 132.16 (C2¢ and C6¢), 129.15 (C3¢ and C5¢), 128.29 (C4¢).
31P NMR (121.50 MHz, CDCl3): d -1.29 ppm. UV-vis. (CH2Cl2,
l
max/nm, e/M-1cm-1): 351 (1.2 ¥ 104), 305 (2.9 ¥ 104), 253 (2.04 ¥
104). srt = 2.76 ¥10-6 S cm-1, Ea = 0.183 eV.
Fig. 11 Temperature dependent electrical conductivities of 1 and 2.
Synthesis of Cu2Ni(L)2(PPh3)4 (2)
Experimental
To a 15 mL aqueous solution of the ligand K2L·2H2O (0.720 g,
2 mmol) was added solid NiCl2·6H2O (0.237 g, 1 mmol), which
after stirring generated a clear green solution of complex salt
K2[NiL2]. Reaction of 20 mL CH2Cl2 solution of Cu(PPh3)2NO3
(1.3 g, 2 mmol) with one equivalent of in situ generated complex
salt K2[Ni(L)2] resulted in the formation of dark brown colored
solution after overnight stirring. The dark brown solid was
collected by the removal of the solvent and dried in vacuo over
CaCl2.
General procedure
All reactions were carried out in open atmosphere at ambi-
ent temperature. The solvents such as dichloromethane, diethyl
ether, methanol, dimethylformamide (DMF) and carbon disulfide
were purchased from Merck and where necessary were purified
by standard procedures prior to their use. NiCl2·6H2O and
Cu(NO3)2·3H2O both SDS, p-methylphenylsulfonamide (Spec-
trochem), K2PtCl4, K2PdCl4, KOH and triphenylphosphine (all
Sigma–Aldrich) were used as received. The dipotassium salt of p-
tolylsulfonyl dithiocarbimate (p-CH3C6H4SO2N CS2K2·2H2O)
ligand was prepared by reaction of p-tolylsulfonamide, KOH
and carbon disulfide according to literature procedure11 and
Yield: (1.34 g, 68%), m.p. 155–158◦ (dec.). Calcd for
C91H80Cl6Cu2N2NiO4P4S6: C 55.19, H 4.07, N 1.41, S 9.71, Ni
2.96, Cu 6.42%. Found: C 55.10, H 4.03, N 1.32, S 9.38, Ni
2.89, Cu 6.35%. IR (KBr, cm-1): 1473 n(C N); 1306 nasym(SO2);
1
1149 nsym(SO2); 987 nasym(CS2). H NMR (300.40 MHz, CDCl3,
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ppm): d 7.98 (d, J = 6.0 Hz, 4 H, H2 and H6), 6.82 (d, J =
6.0 Hz, 4 H, H3 and H5), 2.26 (s, 6 H, CH3), 7.58 (m, 60 H,
PPh3). 13C (75.45 MHz, CDCl3, ppm): d 208.10 (N CS2); 142.04
(C4), 133.88 (C1), 132.16 (C3 and C5), 128.56 (C2 and C6), 21.47
(CH3). Triphenylphosphine signals: 135.01 (C1¢), 133.81(C2¢ and
C6¢), 129.80 (C3¢ and C5¢), 127.81(C4¢). 31P NMR (121.50 MHz,
CDCl3): d 21.57, 4.61 and -0.11 ppm. UV-vis. (CH2Cl2, lmax/nm,
Crystallography
Single-crystal X-ray data and the space group, unit cell dimensions
and intensity data for the complexes were collected on Bruker
Smart Apex (1, 2) and Nonius Kappa CCD (3, 4) diffractometer
˚
using graphite monochromated Mo-Ka radiation (l = 0.71073 A
for 1, 3, 4 and 0.71069 for 2). The crystals were mounted on
a glass fiber. The structures were solved by the direct method
using SHELXS-9713 for 1 and SHELXTL14 for 2 and refined
anisotropically for non-hydrogen atoms by full matrix least-
squares technique using SHELXL–9715 programme package. All
the hydrogen atoms were geometrically fixed and allowed to refine
using a riding, Ref U and constr model. PLATON16 was used
for analyzing the weak interactions, bond distances and angles.
Figure for 1, 2, 3 and 4 were prepared using ORTEP17 In complex
3 and 4, which are isomorphous one phenyl ring was found to be
disordered. Refinement of the disorder showed it to be 49 : 51, so
final refinements were carried out with 1 : 1 disorder.
e/M-1cm-1): 440 (5.5 ¥ 103), 350 (3.7 ¥ 104), 263 (3.9 ¥ 104). srt
1.24 ¥ 10-6 (S cm-1), Ea = 0.186 eV.
=
Synthesis of Pd(PPh3)2L (3)
Reaction of 20 mL CH2Cl2 solution of Cu(PPh3)2NO3 (1.3 g,
2 mmol) with one equivalent of in situ generated complex salt
[K2Pd(L)2] adopting exactly the same procedure as for 2 but using
K2PdCl4 (0.326 g, 1 mmol) led to the formation of yellowish-
brown powder. The dissolution of the powdered compound in
CH2Cl2 yielded yellow crystals in good yield.
Alternatively, 3 could be prepared by the reaction of methanol
solution (25 mL) of triphenylphosphine (0.524 g, 2 mmol) with
an aqueous-methanol (40 : 60) solution (15 mL) of K2L·2H2O
(0.360 g, 1 mmol) producing a clear solution. Solid K2PdCl4
(0.326 g, 1 mmol) was added to the above reaction mixture which
resulted in the formation of yellow solid product after continuous
stirring for about 24 h. The compound thus formed was filtered
off, washed twice with water, followed by diethyl ether and dried
in vacuo over anhydrous calcium chloride.
Computational details
Optimized molecular geometries were calculated using the
B3LYP18 exchange–correlation functional. The spin restricted
DFT method was employed to model the closed-shell species.
The LANL2DZ (d, p) basis set for Pd and Pt atoms, 6-31G**
for C, H, O, N, S and P atoms while 3-21G** for all atoms for
1 was used. The optimized structures of the complex were used
for molecular orbital analyses and time-dependent DFT (TD-
DFT) calculations at the same level of theory with polarized
continuum model (PCM).19 The solvent parameters were those
of the dichloromethane. The energies and intensities of 40 for
1 and 60 for 3 and 4, lowest-energy spin allowed electronic
excitations respectively were calculated using the TD-DFT. All the
calculations were performed using the Gaussian 03 programme.20
The molecular orbital plots were constructed with the MOLDEN
program.21
Yield (0.727 g, 83%), m.p. 190–192◦ (dec.), Anal. calcd for:
C44H37NO2P2PdS3: C 60.31, H 4.26, N 1.60, S 10.98%. Found: C
60.29, H 4.20, N 1.54, S 10.92%. IR (KBr, cm-1): 1438 n(C N),
1301 nasym(SO2), 1142 nsym(SO2), 919 nsym(CS2), 381 n(Pd–S).1H
NMR (300.40 MHz, CDCl3, ppm): d 7.78 (d, J = 6.0 Hz, 2 H,
H2 and H6), 7.36–7.11 (m, 32 H, H3, H5, and PPh3), 2.36 (s,
3 H, CH3). 13C (75.45 MHz, CDCl3, ppm): d 205.38 (N CS2);
141.80 (C4); 134.32 (C1), 130.86 (C3 and C5); 128.61 (C2 and C6);
21.53 (CH3). Triphenylphosphine signals: 134.24 (C1¢), 134.16 (C2¢
1
and C6¢), 128.50 (C3¢ and C5¢), 127.87(C4¢) ppm. 31P{ H} NMR
(121.50 MHz, CDCl3, 20 ◦C): d 30.94 ppm. UV-vis. (CH2Cl2,
max/nm, e/M-1cm-1): 419 (1.4 ¥ 104), 351(3.35 ¥ 104), 325 (3.55 ¥
Conclusion
l
104), 294 (3.53 ¥ 104), 248 (3.8 ¥ 104). ES-MS: m/z = 875.8 [M+].
In conclusion, we have shown three different modes of coor-
dination of the ligand p-tolylsufonyl dithiocarbimate in combi-
nation with PPh3 within the same molecule which resulted in
the formation of unique homodi-, trinuclear heterometallic and
heteroleptic complexes. The trinuclear heterometallic complex 2
has three distinct-geometries in a single entity. Preparation of the
analogous trinuclear heterometallic complexes with soft metal ions
palladium(II) and platinum(II), instead yielded the mononuclear
complex M(PPh3)2(dithiocarbimate) via PPh3 transfer because
of the greater propensity of these metals to adopt square pla-
narity compared to nickel(II). In the heteroleptic complexes of
palladium(II) and platinum(II) rare intramolecular C–H ◊ ◊ ◊ M,
anagostic interactions were identified in the crystal structures.
These are unique examples with MP2S2 chromophore involving
ortho phenyl protons of the PPh3 ligand. All complexes exhibit
photoluminescence emission in solution at room temperature. The
TD-DFT calculations show that the intra ligand charge transfer
transitions are primarily responsible for their photoluminescent
emissions. The di- and trinuclear heterometallic complexes show
Synthesis of Pt(PPh3)2(L) (4)
This colourless complex was prepared in good yield adopting
exactly similar procedures for 3 using K2PtCl4 (0.415 g, 1 mmol).
Yield (0.753 g, 78%), m.p. 192–195◦ (dec.), Anal. calcd for
C44H37NO2P2PtS3: C 54.77, H 3.86, N 1.45, S 9.97%. Found: C
54.65, H 3.80, N 1.43, S 9.94%. IR (KBr, cm-1): 1453 n(C N);
1305 nasym(SO2); 1145 nsym(SO2); 997 nasym(CS2); 348 n(Pt–S).1H
NMR (340.40 MHz, CDCl3, ppm): d 7.76 (d, J = 9.0 Hz, 2 H,
H2 and H6), 7.38–7.11 (m, 32 H, H3, H5 and PPh3), 2.37 (s,
3 H, CH3). 13C (75.45 MHz, CDCl3, ppm): d 210.67 (N CS2);
141.94 (C4); 134.38 (C1), 130.98 (C3 and C5); 128.65 (C2 and C6);
21.54 (CH3). Triphenylphosphine signals: 134.36 (C1¢); 134.23 (C2¢
and C6¢); 128.60 (C3¢ and C5¢); 127.86 (C4¢) ppm. 31P{ H} NMR
1
(121.50 MHz, CDCl3, 20 ◦C): d 18.97 ppm, J195
= 3112.10 Hz.
31
Pt–
P
UV-vis. (CH2Cl2, lmax/nm): 335 (3.67 ¥ 104), 296 (3.74 ¥ 104), 248
(3.98 ¥ 104). ESI-MS: m/z = 965 [M+].
630 | Dalton Trans., 2011, 40, 623–631
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semiconductor behaviour whereas the heteroleptic complexes are
insulators.
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Acknowledgements
We acknowledge the council of scientific and industrial research
(CSIR) for funding (project no. 01(2290)/09/EMR-II, New
Delhi), Dr A. Mishra, for fluorescence spectra and Dr Abhinav
Kumar, Lucknow University for theoretical calculation assistance.
We thank EPSRC (UK) and the University of Reading for funds
for the diffractometer.
8 (a) S. P. Kaiwar, A. Vodacek, N. V. Blough and R. S. Pilato, J. Am.
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