Polyhedron 52 (2013) 900–908

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Polyhedron

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Photoluminescent Mo(IV) and W(IV) bis-dithiolene complexes with bidentatephosphonodithioato ligand derived from Lawesson’s reagent

Golam Moula, Moumita Bose, Harashit Datta, Sabyasachi Sarkar ⇑Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur-208016, India

a r t i c l e i n f o a b s t r a c t

Article history:Available online 20 July 2012

Dedicated to Alfred Werner on the 100thAnniversary of his Nobel prize in Chemistryin 1913.

Keywords:DithioleneLawesson’s reagentPhosphonodithioatoPhotoluminescentOxygen atom transferDFT

0277-5387/$ - see front matter � 2012 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.poly.2012.07.024

⇑ Corresponding author.E-mail address: abya@iitk.ac.in (S. Sarkar).

Synthesis of phosphonodithioato complexes of Mo(IV) and W(IV) bis- dithiolene have been reported.These complexes are characterized by elemental analysis, X-ray crystallography, IR, UV–Vis, 31P NMR,and photoluminescence spectroscopy, electrochemical studies and these results are corroborated byDFT level of calculations. Phosphonodithioato ligands is generated in situ from the reaction of Lawesson’sreagent with mono-oxo Mo/W bis dithiolenes complexes resulting its chelation coupled with oxo transferreaction from M(IV) bound oxo to {P=S} moiety forming (P=O} group. The new complexes are photolumi-nescent at room temperature.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

The oxygen atom transfer (OAT) chemistry of Mo and W com-plexes are extensively studied to model Mo and W oxotransferases[1]. The function of these enzymes are very crucial to maintain dif-ferent forms of life and in turn by controlling the global bio-geo-chemical cycles of nitrogen, carbon, sulfur and arsenic [2–4]. Anumber of Mo and W oxo sulfide complexes found applicationsin catalysis also [5–7]. All oxo transfer molybdoenzymes such assulfite oxidase, nitrate reductase, dimethyl sulfoxide reductaseetc. are ligated with pyranopterin ene dithiolate (Mo-cofactor)through sulfur atoms [8]. Compare to Mo, OAT reaction is less com-mon with W but are exclusive in the hyperthermophilic metallo-proteins of archaeal origin [9–13].

Amongst model molybdoenzymes oxo molybdenum complexesare common but for xanthine oxidase or dehydrogenase type of en-zymes instead of dioxo [MoVI(O2)] core, [MoVI(OS)] core exists [8].Several methodologies were tried to convert bound oxo group tosulfido form and in this aspect the conversion of {M = O}(M = Mo, W) to {M = S} has been shown by Holm and co-workers[14] using Lawesson’s reagent (Fig. 1). This is very similar to theuse of Lawesson’s reagent for the conversion of carbonyl group tothio-carbonyl [15].

Chemistry of Lawesson’s reagent has been studied for manyyears [15]. Reactions of this reagent with organic substrates are

ll rights reserved.

well known but with transition metals less investigation has beenmade. So far the mode of reaction of Lawesson’s reagent to a tran-sition metal showed different mode of its coordination [16] (Fig. 2).

In a reaction of Lawesson’s reagent with transition metals, itmay undergo two types of cleavage – (i) symmetrical and (ii)unsymmetrical [17] (Fig. 3).

Phosphonodithioate complexes are known to possess biologi-cally relevant properties [18]. Phosphonodithioate is one of theS-donor ligands families which include phosphorodithioates andphosphinodithioates (Fig. 4). These types of ligands can be derivedfrom monoprotic acids as mono-negative anions or from diproticacids as di-negative anions (Fig. 4) [19].

Metal complexes with phosphodithioates as ligand have manycommercial applications. These are used as floatation reagentsfor the recovery of metals from their solutions, additives to lubri-cant oils, pesticides and for also chemical warfare [20]. An interest-ing use of this ligand to form liquid transition metal complexesspecifically of Pt for the use in the preparation of thin layer bychemical vapor deposition (CVD) or by creating polymer–inorganicnanocomposites [21]. Tin diphenyldithiophosphinato complexesexhibit considerable antiproliferation activity towards certain leu-kaemia cells [22].

Synthesis, chemistry and structural studies of phosphorodithio-ates and phosphinodithioates complexes are widely spread in theliterature [19,21–31] compared to phosphonodithioate complexesbecause of the difficulty in its synthesis [32]. Few structurally char-acterized uni-negative phosphonodithioate [33–35] and dinegativephosphonodithioate complexes [36–42] are known and the

Fig. 2. Coordination motifs of fragment derived from Lawesson’s reagent. Mindicates the metal.

Fig. 1. Lawesson’s reagent {(p-methoxyphenyl) thionophosphine sulfide}.

G. Moula et al. / Polyhedron 52 (2013) 900–908 901

formation of dinegative phosphonodithioate bound Ni, Pd and Ptcomplexes in solution have been made by IR and 31P NMR [43].

We were interested to convert mono-oxo Mo (and W)bis(dithiolene) complex into the corresponding sulfido analogusing this reagent to mimic the reduced DMSO reductase model[44]. We were hopeful that the proposed reaction should have fol-lowed a similar pathway as described by Holm and co-workers[14] but instead we could isolate phosphonodithioate bound bis(dithiolene) trigonal prismatic complexes. Here we report the syn-thesis and chemistry of molybdenum and tungsten complexes ofthe dinegative phosphonodithioate ligand which has been derivedin situ from the cleavage of Lawesson’s reagent. This work shows adifferent type of oxygen atom transfer reaction by Lawesson’sreagent toward Mo and W mono oxo complex where a part of

Fig. 3. Symmetrical and unsymmetrica

the reagent is ligated to Mo or W, and the oxygen atom of{Mo=O} or {W=O} moiety is transferred to phosphorus of theLawesson’s reagent through a reaction that necessarily involvethe well known Wittig reaction (Fig. 5). Here the driving force ofthis reaction is due to the formation of a stable P=O double bond.

2. Experimental

2.1. Materials

All reactions and manipulations were performed underambient conditions. Reagents and solvents were purchased fromcommercial sources and used as received. Na2mnt (mnt2� =S2C2(CN)2

2� = 1,2-dicyanoethylenedithiolate) was prepared by themethod of Stiefel et al. [45] [Bu4N]2[MoIVO(mnt)2] (1) [46] and[Et4N]2[WIVO(mnt)2] (2) [47] were prepared following the processreported earlier.

2.2. Physical measurements

Elemental analyses for carbon, hydrogen, nitrogen and sulfurwere performed with a Perkin-Elmer 2400 microanalyser. Infraredspectra were recorded on a Bruker Vertex 70, FT-IR Spectropho-tometer as pressed KBr disks. Electronic spectra were recordedon Lambda 35 UV/VIS Spectrometer (Perkin-Elmer) with PCB150/PTP-6 Peltier System. The photoluminescence (PL) emissionsand excitations were recorded in Perkin Elmer LS55 fluorescencespectrometer by using quartz cells of 10 mm path length for exci-tation slit 15 nm and emission slit 10 nm. Cyclic voltammetricmeasurements were made with a BASi Epsilon-EC BioanalyticalSystems, Inc. instrument. Cyclic voltammograms of 10�3 M solu-tion of the compounds were recorded with a glassy carbon elec-trode as working electrode, 0.2 M Bu4NClO4 as supportingelectrolyte, Ag/AgCl electrode as reference electrode, and a plati-num auxiliary electrode. All electrochemical experiments weredone under argon atmosphere at 298 K. Potentials are referenced

l cleavage of Lawesson’s reagent.

Fig. 4. Different types of phosphodithioate ligands.

Fig. 5. Diverse reactivity of Lawesson’s reagent with {M=O} moiety.

902 G. Moula et al. / Polyhedron 52 (2013) 900–908

against internal ferrocene (Fc) and are reported relative to the Ag/AgCl electrode (E1/2(Fc+/Fc) 0.459 V versus Ag/AgCl electrode). 31P

NMR in dichloromethane were recorded by a JEOL JNM – LA 500,FT-NMR spectrometer.

G. Moula et al. / Polyhedron 52 (2013) 900–908 903

2.3. Synthesis

2.3.1. Synthesis of [Bu4N]2[MoIV(mnt)2{S2P(O)C6H4(OCH3)}]�Et2O (3)To a solution of 0.088 g (0.1 mmol) of [Bu4N]2[MoO(mnt)2] in

10 mL acetonitrile, 0.04 g (0.1 mmol) of Lawesson’s reagent wasadded with constant stirring. The starting green colored solutionchanged into light brown and finally to deep-violet. Stirring wascontinued for 2 h. To this violet solution, �35 mL diethyl etherwas added and it was allowed to stand at 4 �C for 2 days. Deep-vio-let colored block shaped diffraction quality crystals appeared. Thecrystals were filtered, washed with diethyl ether and dried at roomtemperature. Yield: 0.087 g (81%). Required for C51H89MoN6O3PS6:C, 53.10; H, 7.78; N, 7.29; S, 16.68. Found: C, 53.23; H, 7.81; N,7.44; S, 16.57%. IR (KBr pellet): m1479 (C=C), 2200 (C�N), 1239(P=O), 2874, 2962 (CH stretching), 737 (CH bending) cm�1. kmax

(eM in M�1 cm�1) in acetonitrile: 341 (10127), 384 (6150), 416(sh) and 535 (7530) nm.

2.3.2. Synthesis of [Bu4N]2[WIV(mnt)2{S2P(O)C6H4(OCH3)}] .Et2O (4)To a solution of 0.074 g (0.1 mmol) of [Et4N]2[WO(mnt)2] in

10 mL acetonitrile 0.04 g (0.1 mmol) of Lawesson’s reagent wasadded with constant stirring. The starting pink colored solutionchanged to orange red. Stirring was continued for 2 h followedby addition of 0.2 g (0.5 mmol) of tetrabutyl ammonium bromide.Then the mixture was stirred for another 1 h. To this orange redsolution, �35 mL diethyl ether was added and it was allowed tostand at 4 �C for 2 days. Deep-brown colored block shaped diffrac-tion quality crystals are separated out. These crystals were filtered,washed with diethyl ether and dried at room temperature. Yield:0.094 g (76%). Required for C51H89WN6O3PS6: C, 49.34; H, 7.23;N, 6.77; S, 15.50. Found: C, 49.23; H, 7.34; N, 6.85; S, 15.47%. IR(KBr pellet): m 1486 (C=C), 2199 (C�N), 1240 (P=O), 2874, 2962(CH stretching), 737 (CH bending) cm�1. kmax (eM in M�1 cm�1) inacetonitrile: 354 (6270), 367 (sh), 445 (6230) and 509 (3060) nm.

2.4. X-ray crystallography

Suitable diffraction quality crystal of complex 3 (and of 4) wasglued to glass fiber and mounted on a BRUKER SMART APEX dif-fractometer. The instrument was equipped with a CCD area detec-tor, and data were collected using graphite-monochromated MoKa radiation (k = 0.71069 Å) at low temperature (100 K). Cell con-stants were obtained from the least-squares refinement of threedimensional centroids through the use of CCD recording of narrowx rotation frames, completing almost all-reciprocal space in thestated h range. All data were collected with SMART 5.628 (BRUKER,2003), and were integrated with the BRUKER SAINT program [48].The structure was solved using SIR 97 [49] and refined usingSHELXL-97 [50]. Crystal structures were viewed using ORTEP [51].The space group of the compounds was determined on the basisof systematic absence and intensity statistics. Full-matrix least

Scheme 1. Schematic representation

squares/difference Fourier cycles were performed which locatedthe remaining non-hydrogen atoms. All non-hydrogen atoms wererefined with anisotropic displacement parameters.

2.5. Computational details

All calculations were performed using the Gaussian 03 (Revi-sion B.04) package [52] on an IBM PC platform. Gas phase geome-try optimization and population analysis of the molecular orbitalswere carried out at DFT level. The method used was Becke’s threeparameter hybrid exchange functional [53], the non-local correla-tion provided by the Lee, Yang and Parr expression [54] (ROB3LYP).6-31G⁄+ basis set [55] was used for C, H, N, S, O and P atoms. TheLANL2DZ basis set [56] and LANL2DZ pseudo potentials of Hay andWadt [57,58] were used for the Mo and W atoms. The optimizedminima were characterized by harmonic-vibration-frequency cal-culation with the same method and basis set in which the mini-mum has no imaginary frequency. For geometry optimization,initial coordinates were taken from the corresponding crystalstructure data of complexes 3 and 4. Gas phase single point calcu-lations and population analysis of molecular orbital were carriedout by taking xyz coordinates of optimized geometries. Molecularorbitals were visualized using ‘Gauss View’. The assignment ofthe type of each MO was made on the basis of its compositionand by visual inspection of its localized orbital.

3. Results and discussion

3.1. Synthesis

Reaction of [MIVO(mnt)2]2� (M=Mo, W) with Lawesson’s re-agent, yielded phosphonodithioate bound trigonal prismatic com-plex (Scheme 1).

The high yield of this reaction showed that it is a neat reaction.The phosphonodithioate ligand is generated in situ through a thia-oxaphosphetane intermediate (Fig. 5). The driving force of thisreaction is the formation of a stable {P=O} bond. Such transferhas the similarity with the well known Wittig reaction. Holmand co-workers when used this reagent to convert {Mo=O} to{Mo=S} the Mo complex used has been with hexa coordinationand the product was also hexa coordinated [14]. Interestingly inthe present case the starting complex was penta coordinated andthere was a room for coordination expansion. The in situ generatedphosphonodithioate ligand being bidentate did chelate the metalreadily thus adding extra stability.

3.2. Description of structures

The crystal structures of the anionic complexes of 3, and 4 areshown in Figs. 6 and S1, respectively. The leading structural

for the synthesis of complexes.

Fig. 6. Structure (ORTEP view) of the anion of [Bu4N]2[MoIV(mnt)2{S2P(O)-C6H4(OCH3)}] (3) showing 50% probability thermal ellipsoids with selected atomlabeling scheme.

Table 2Selected bond distances (Å) for complexes 3.and 4.

Distances (Å) Complex 3 Complex 4

M(1)–S(1) 2.359(19) 2.359(18)M(1)–S(2) 2.358(17) 2.358(19)M(1)–S(3) 2.381(18) 2.376(18)M(1)–S(4) 2.373(18) 2.374(19)M(1)–S(5) 2.429(2) 2.424(19)M(1)–S(6) 2.443(18) 2.435(19)P(1)–O(1) 1.493(4) 1.493(5)P(1)–S(5) 2.058(2) 2.064(3)P(1)–S(6) 2.057(2) 2.065(2)

Table 3Selected angles (�) for complexes 3.and 4.

Angles (�) Complex 3 Complex 4

O(1)–P(1)–C(9) 108.8(3) 109.2(3)O(1)–P(1)–S(6) 117.23(19) 117.3(2)O(1)–P(1)–S(5) 117.7(2) 117.7(2)C(9)–P(1)–S(6) 108.7(2) 108.8(2)C(9)–P(1)–S(5) 108.0(2) 108.2(2)S(6)–P(1)–S(5) 95.40(9) 94.56(10)P(1)–S(5)–M(1) 93.53(7) 93.99(9)P(1)–S(6)–M(1) 93.18(7) 93.66(8)S(2)–M(1)–S(4) 84.68(6) 142.15(6)S(1)–M(1)–S(4) 142.34(7) 84.16(7)S(2)–M(1)–S(3) 131.02(6) 81.06(7)S(4)–M(1)–S(3) 81.41(6) 81.65(7)S(5)–M(1)–S(6) 77.32(5) 77.27(6)S(3)–M(1)–S(6) 141.58(6) 140.70(6)S(4)–M(1)–S(6) 82.97(6) 82.87(6)S(2)–M(1)–S(6) 81.76(6) 129.70(6)S(1)–M(1)–S(6) 129.38(6) 81.96(6)

904 G. Moula et al. / Polyhedron 52 (2013) 900–908

parameters are collected in Table 1 and the selected bond distancesand angles are listed in Tables 2 and 3.

The presence of two counter mono-cations suggest an overall2(�) charge on the anion of the complexes 3 and 4 that is consis-tent with the assignment of the formal oxidation state of boththe metal as IV. The metal atom(s) are in trigonal prismatic geom-etry. The phosphorus atoms reside in a pseudo-tetrahedral envi-ronment with the 4-methoxyphenyl and oxo groups transdisposed with respect to the coordination plane defined by theP(1), S(5) and S(6) atoms (Fig. 7).

Mo atom is 0.872 ÅA0

above from the dithiolene sulfur basalplane, (Fig. 8(b)) whereas W atom is 0.868 ÅA

0

above from the dithio-lene sulfur basal plane. P–S bond distances (Table 2) indicate singlebond [59] character suggesting the phosphonodithioate ligand is indi- anionic state in these complexes. Both the molecules have a

Table 1Crystallographic dataa for complexes 3 and 4.

Complexes 3 4

Formula C51H79MoN6O3PS6 C51H89WN6O3PS6

Formula weight 1143.47 1241.46Crystal system triclinic triclinicSpace group P�1 P�1T (K) 100 100Z 2 2a (Å) 10.863 (5) 10.908 (5)b (Å) 12.417 (5) 12.499 (5)c (Å) 24.839 (5) 24.807 (5)a (�) 99.246 (5) 76.568 (5)b (�) 95.158 (5) 85.041 (5)c (�) 115.459 (5) 64.300 (5)V (Å3) 2937.9 (19) 2963.8 (19)dcalc (g/cm3) 1.293 1.391l (mm�1) 0.507 2.231h range (�) 1.69–27.00 2.11–26.00GOF (F2) 1.149 1.013R1

b (wR2c) 0.0721 (0.2438) 0.0534 (0.611)

a Mo Ka radiation.b R1 =

P||F0| � |Fc||/

P|F0|.

c wR2 = {P

[w(F02 � Fc

2)2]/P

[w(F02)2]}1/2.

Fig. 7. Plane showing oxo and 4-methoxy-phenyl groups are trans with respect topseudo tetrahedral phosphorus.

pseudo-point group in the solid state as the plane containingO–P–M (Fig. 8(a)) is bisecting the molecule into two halves.

3.3. Infra-red spectra

The characteristic m(Mo=O) at 928 cm�1 present in the staringmono-oxo molybdenum complex [46] (Fig. S3) disappeared incomplex 3 (Fig. S5). Similarly m(W=O) at 934 cm�1 of the starting

Fig. 8. (a) Plane containing O–P–Mo is bisecting the molecule which reveals themolecule has pseudo-point group in the solid state. (b) Mo atom is 0.872 Å abovefrom the dithiolene sulfur basal plane.

G. Moula et al. / Polyhedron 52 (2013) 900–908 905

tungsten complex [47] (Fig. S4) disappeared in the IR spectrum of 4(Fig. S6). The presence of {P=O} moiety is confirmed on the basis ofthe appearance of a strong band around �1240 cm�1. Interestinglythe band at 687 cm�1 which is present in the Lawesson’s reagent(Fig. S2) due to m(P=S) is now absent in 3 and 4 suggesting theoxo transfer reaction complimentary to the presence of {P=O}bond.

3.4. UV–Vis spectroscopic measurements

Complexes 3 and 4 are stable in acetonitrile solvent. The elec-tronic spectrum of 3 consists of four bands with kmax (eM) = 341(10127), 384 (6150), 416 (sh) and 535 (7530) nm as shown inFig. 9. Similarly, the electronic spectrum of 4 also consists of fourbands with kmax (eM) = 354 (6270), 367 (sh), 445 (6230) and 509

Fig. 9. UV–Vis absorption spectrum (10�4 M in acetonitrile) of complex (3) (black)and complex (4) (red). (Color online.)

(3060) nm (Fig. 9). Band around 340–385 nm is associated withthe internal transition of the dithiolene ligand mixed with internaltransition from phosphonodithioate while the intense bands thatextend into the visible region correspond to charge transfertransition.

3.5. Electrochemistry

The electrochemical properties of these complexes were inves-tigated by both oxidative and reductive scans in cyclic voltamme-try (Fig. 10). Complex 3 exhibited two irreversible oxidation steps.Both of the oxidation wave at Epa = 0.61 V and Epa = 1.04 V are dueto the oxidation of the coordinated sulfur of the coordinated male-onitriledithiolene ligand. Such oxidation is common in other male-onitriledithiolene coordinated complexes. In addition, it exhibitsone reversible reduction at E1/2 = �1.17 V which may be metal cen-tered reduction. The third reduction at Epc = �1.92 V is due to thereduction of coordinated maleonitriledithiolene ligand (mnt2�).For complex 4, the first reversible reduction at E1/2 = �1.45 V andirreversible oxidation at Epa = 0.44 V both have been consideredas metal centered, as its HOMO and LUMO contain metal orbital(see Fig. 13). One almost merged oxidation around Epa = 0.54 V(for coordinated mnt2� ligand oxidation)along with the oxidationwave at Epa = 0.44 V has been observed .The second reduction atEpc = �1.92 V and second oxidation Epa = 1.04 V are associated withligand mnt2� as both the complexes show this peaks roughly at thesame potential. For the reductive scan one additional wave atEpa = 0.14 V arises for complex 4 which is because of the oxidationof reduced species formed during reduction.

3.6. Photoluminescence

Both of the complexes 3 and 4 are luminescence active becauseof the presence of phosphodithioate ligand (Figs. 11 and 12). Trisdithiolene complexes are reported to be luminescence inactive[60]. Upon excitation with either 341 or 384 nm light complex 3shows photoluminescence in the blue region with peak maxima445 nm in acetonitrile. When acetonitrile solution of complex 4was excited with either 354 or 367 nm light, blue luminescencewith a maximum at 420 nm is observed. Both the complexes areluminescence inactive with other absorptions present in electronicspectra. As tris dithiolene complexes do not show such lumines-cence it is expected that the absorption bands at 341 and 384 nmin 3 or 354 and 367 nm in 4 are strongly involved with phosphodi-thioate ligand.

3.7. 31P NMR spectra

The proton decoupled 31P NMR measurements are carried out indichloromethane solution for free Lawesson’s reagent, complex 3and complex 4, respectively. The 31P NMR peak signal in unboundLawesson’s reagent is observed at d = 17.49 ppm (Fig. S7). The 31PNMR peak in complex 3 appeared at d = 103.54 ppm (Fig. S8) andthat for complex 4 at d = 127.52 ppm (Fig. S9), respectively (phos-phoric acid as reference). Such drastic shift in d values arise be-cause the phosphonodithiato ligand is bound to molybdenum(IV)and tungsten(IV), respectively.

4. Density functional theory

The stability and electrochemical behavior of these complexescan be compared in the light of relative energy levels of theirmolecular orbitals at least in a qualitative sense in the gas phase.

Stability of the complex 3, in comparison to the stability of thecomplex 4 is in agreement with the relatively lower energy HOMO

Fig. 10. Cyclic voltammetric traces (scan rate = 100 mV/s) (a) for complex (3) and (c) for complex (4) in acetonitrile; oxidative scan (black solid line) and reductive scan (reddotted line). Reversible redox couple (b) at E1/2 = �1.17 V for complex (3) and (d) E1/2 = �1.45 V for complex (4) at different scan rates, 50, 100, 200, 300, 400, 500 to 600 mV/s.(Color online.)

Fig. 11. Excitation (left dotted line) and photo-luminescence spectra of complex(3).

Fig. 12. Excitation (left dotted line) and photo-luminescence spectra of complex(4).

906 G. Moula et al. / Polyhedron 52 (2013) 900–908

(Fig. 13) in the case of 3 (�0.18 eV). The HOMO of the complex 3 ispredominantly ligand centered whereas HOMO of the complex 4 is

predominantly metal centered. The orbitals present in HOMO andHOMO-1 in the molybdenum complex 3 are essentially inter-

Fig. 13. Relative energies of HOMOs and LUMOs of complex anions 3 and 4.

G. Moula et al. / Polyhedron 52 (2013) 900–908 907

changed in the tungsten complex 4. Further the HOMO of 3 and theHOMO-1 of complex 4 have nearly the same stabilization energy.

The subtle changes in the order of HOMO’s in 3 and 4 can be ob-served in the electrochemical study. An oxidation at Epa = �0.6 V inthe case of 3 is attributed due to its low lying ligand centeredHOMO. An oxidation at Epa = 0.44 V in the case of 4 (Fig. 10) isdue to its metal centered HOMO. A nearly merged oxidation pro-cess at Epa = �0.6 V in the case of 4 is observed. This is becauseHOMO-1 for complex 4 and HOMO of complex 3 are both ligandcentered. The LUMOs and LUMO-1 orbitals are metal centered forboth of molybdenum and tungsten complexes.

5. Conclusions

Reacting Lawesson’s reagent directly with the coordinativelyunsaturated M(IV)-oxo complex (M = Mo, W), phosphonodithioatometal complexes can be synthesized as the sole product. Metal trisdithiolene complexes are not photoluminescent, but for the coordi-nation of phosphonodithioato type of ligand, this complexes withthree bidentate ligand’s coordination showed photoluminescence.The detailed photoluminescence properties of this type of com-plexes could be of interest and such study is under progress.

Acknowledgments

G. M. and M. B. thank the Council of Scientific and Industrial Re-search (CSIR), New Delhi for the award of doctoral fellowships. H.D. thanks S. S. for allowing a part of this work as his M. Sc. projectunder his guidance. S. S. thanks the Department of Science andTechnology (DST), New Delhi for funding.

Appendix A. Supplementary data

Structure (ORTEP view) of the anion of complex 4, Infra-redspectra, 31P NMR spectra of all the complexes including Lawesson’sreagent are available. Crystallographic data (including structurefactors) for the two crystals for complexes 3 and 4 have beendeposited in the Cambridge Crystallographic Data Centre. CCDC873768 and 873767 contains the supplementary crystallographicdata for complexes 3 and 4, respectively. Copies of the data canbe obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Cen-tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data asso-ciated with this article can be found, in the online version, athttp://dx.doi.org/10.1016/j.poly.2012.07.024.

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