Indian Journal of Chemistry Vol. 42A, September 2003, pp. 2344-2351

Synthesis, characterization and structural studies of metal complexes based on dmit, dmt and tbs ligands. Crystal structure of [PPNHAu(dmith].CH3CN

Kochurani', K Kandasamy', H B Singh*" & Babu Vargheseb

"Department of Chemistry, Indian Institute of Technology Bombay, Pow ai, Mumbai 400 076, India

bRSIC, Indian Institute of Technology Madras, Chennai 600 036, India

Received 2 January 2003

Dichalcogenene complexes of the formula [cationln[M(dmithr, [cationln[M(dmthln- and [cationln[M(tbshl"­[M = Ni, Cu, Pd, Pt; Au, n = 0-2; dmit = 4,5-dimercapto-l.3-dithiole-2-thione. dmt = 4.5-dimercapto-l,2-dithiole-3-thione and tbs = thiobenezeneselenolate. cation = trimethyltelluronium, (CH3hTe+. bis(triphenylphosphine)iminium, PPN+, tetrabutylammonium. BU4N+, and trimethylammonium. Me3NH+l have been prepared. The spectroscopic and electrochemical behaviour have been studied and compared with the related complexes. Oxidation reactions of these complexes with iodine afforded partially oxidized derivatives which exhibit compressed electrical conductivites of > 10--6 S cm-1 at room temperature. The [PPN)[Au(drnithl complex has been structurally characterized by X-ray crystallography and its structure is compared with the structure of previously reported complexes [(CH3hTe][Au(dmithl and [PPN][Ni( dmith].

Introduction Currently there is much interest in the study of

planar metal complexes of dichalcogenene and mixed chalcogenene ligands because of their metallic and superconducting properties l

-9. Several of their charge­

transfer salts in this category exhibit superconducting properties. These include (NMe4)0.5[Ni(dmith]10, ~-(NMe4)O.5[Pd(dmit)2]11, (NMe2Et2)o.5[Pd(dmit)2]12 contammg closed-shell cations and (TTF)-[Ni(dmit)2h13

, a-a'-(TTF)-[Pd(dmithh 14, a-(EDT­TTF)[Ni(dmithl 15 containing open-shell cations. Highly conducting Langmuir-Blodgett films based on Au(dmit)z16, and Ni(dmit)z17 anions have also been reported. In addition, these metal complexes find applications in non-linear optics 18 and in the preparation of polymeric materials exhibiting photorefracti vi ty!9.

Recent detailed studies have shown that the change of central metal ions or cations affect their conducting properties. The synthesis and characterization of [M(dmithl and [M(dmthl (where M = Sell and Tell ) type complexes with ClhTe+ along with other cations have reported earlier2o. These complexes were expected to behave as excellent electrical conductors because of the greater polarizability and size of Se & Te than sulphur which can have very effective secondary interactions with anions to give multi­dimensional structures. However, attempts to partially oxidize these complexes led to complete oxidation of the complexes to insulating materials.

This paper reports the synthesis of [M(dmithl"-, [M(dmthr and [M(tbshr (M = Au. Cu, Ni, Pd and Pt) complexes with trimethyltelluronium cation and other cations. ESR studies have been carried out extensively to explain their interesting magnetic properties. A single crystal X-ray structure of [PPN] [Au(dmithl is described and compared with the reported structures of [(CH3hTe] [Au(dmit)z]21 and [PPN] [Ni(dmit)z] 22. Also there is relatively little chemistry reported for the mixed S-Se, S-Te and Se­Te analogues23, while much of the recent work has been focussed on the synthesis of metal complexes with dichalcogenenes. Therefore, we have synthesized [M(tbshr (tbs = thiobenzeneselenolato) complexes with various cations and characterized by spectroscopic and electrochemical techniques in order to compare their properties with their SUlphur bdt (benezenedithiolene) and bds (benezenediselenolene) analogues. OUf convenient synthetic approach to tbs2

-

has also proved useful for the synthesis of variety of organo-sulphur-selenium heterocyc1es24

•

Materials and Methods Reagents used for the research work were selenium

powder (Fluka), tetrabutylammonium bromide (Fluka), NiClz6H20, ZnClz, CuCI2, PdClz (E. Merck, India). KAuC4, K2PtCl4 (Aldrich). trimethylammonium chloride (Fluka), n-butyllithium (E. Merck). All solvents were obtained from commercial sources and were purified25 . In general,

KOCHURANI et al.: CRYSTAL STRUCTURE OF [PPN][Au(dmith].CH)CN 2345

all solvents were distilled prior to use and stored over molecular sieves. All the reactions were carried out under argon with standard Schlenk techniques unless otherwise stated. The dmit ligand was obtained in large quantities as the main product by chemical reduction of carbon disulphide in DMF and was stored as its dibenzoyl salt26. Isomerisation of dmit at 1400 in DMF gave the disodium salt of dmt in solution. This was isolated as its zinc salt and converted to the benzoyl ester by reacting with benzoyl chloride in acetone27. Trimethyltellurium iodide was prepared by literature method2s. The iodide was converted to the chloride by reacting with sil ver chloride29.

[M(dmith] complexes of Ni, Cu, Pd Pt and Au with trimethyltelluronium cation were prepared following a general procedure and a typical example is given below.

Synthesis of [(CH3hTeh[Ni(dmithl 1 The benzoyl ester of the ligand dmit (2 mmol ) was

mixed with sodium methoxide solution (2 ml, 2M) and stirred for 10 min. NiCb6H20 (1 mmol) in methanol (50 ml) was added to this and stirred for another 10 min . To this solution trimethyltelluronium chloride (2 mmol) in methanol (20 ml) was added and the stirring was continued. After 1 h the black solid, which precipitated out, was filtered, washed with methanol and dried under vacuum. This solid was recrystallized from 1: 1 acetone-isopropanol mixture to give a black crystalline solid; yield, 69%. Anal. Found: C, 17.17; H, 2.27; Calcd. for CI2HISTe2NiSJO: C, 18.09; H, 2.28. IR (KBr pellet) vs(C=C) 1460, vs(C=S) 1060 and 1040, vs(C-S) 930 em-I. UV/vis Amax (nm) 585, 402 and 314.

[(CH3hTeI2[Cu(dmithl 2; yield, 62%. Anal. Found: C, 18.07; H, 2.03; Calcd. for CI2HISTe2CuSIO: C, 17.98; H, 2.26. IR (KBr pellet) vs(C=C) 1430, vs(C=S) 1070 and 1040, vsCC-S) 910 em-I. UV/vis Amax (nm) 523, 386 and 303.

[(CH3hTej[Pdf.dmithl 3; yield, 69%. Anal. Found: C, 16.23; H, 1.43; Calcd. for C9H9TePdS JO: C, 16.09; H, 1.35. IR (KBr pellet) vsCC=C) 1360, vs(C=S) 1050 and 1040, vs(C-S) 940 em-I. UV/vis Amax (nm) 490, 384 and 274.

[(CH3hTej[Au{dmithl 5; yield, 62%. Anal. Found: C, 13.85; H, 1.24; Calcd. for C9H9TeAuSJO: C, 14.18; H, 1.19. IR (KBr pellet) vs(C=C) 1360, vsCC=S) 1060 and 1040, vs(C-S) 920 em-I. UV/vis Amax (nm) 463, 346 and 289.

Synthesis of [(CH3hTeh[Pt(dmithl 4 The benzoyl ester of the ligand (2 mmol) was

dissolved in sodium methoxide (7 ml, 2M) to give a red coloured solution. An aqueous solution of potassium tetrachloroplatinate (1 mmol, 20 ml water) was added and stirring continued for half an hour. Trimethyltelluronium chloride (2 mmol) dissolved in methanol (20 rnI) was added to the reaction mixture. The black precipitate was collected by filtration after 1 h. The black solid was recrystallized from 1: I acetone-isopropanol mixture; yield, 71 %. Anal. Found: C, 16.08; H, 1.93; Calcd. for CI2HISTe2PtSIO: C, 15.44; H, 1.94. IR (KBr pellet) vs(C=C) 1430, vs(C=S) 1050 and 1030, vs(C-S) 910 em-I . UV/vis Amax (nm) 422, 269 and 320.

Synthesis of [PPNh[[Cu(dmithl 6 The dibenzoyl ester of the ligand (2 mmol) was

treated with sodium methoxide solution (7 mI, 2M) and stirred for 10 min. CuCh (1 mmol) in methanol (50 rnI) was added to this followed by bis(triphenylphosphine)iminium chloride (2 mmol) in methanol (20 rnI) . The reaction mixture was stirred for 30 min. The dark coloured solid, which precipitated out, was filtered, washed with propanol and dried under vacuum. The product was recrystallized from 1: 1 acetone-isopropanol mixture to give crystals of [PPNh[Cu(dmith]; yield, 73%. Anal. Found: C, 60.65; H, 3.94; N, 1.73; Calcd. for C78H60P4N2CuSJO: C,61.09; H, 3.94; N, 1.83. IR (KBr pellet) vs(C=C) 1445, vs(C=S) 1060 and 1035, vs(C-S) 910 em-I. UV/vis Amax (nm) 456,385 and 308.

Synthesis of [PPNj[Au(dmithl 7 The [PPN][Au(dmit)2] was prepared following the

above procedure with methanolic solution of KAuCI4 ;

yield, 78%. Anal. Found: C, 45.01; H, 3.01; N, 1.61 ; Calcd. for C42H30P2NAuSIO: C, 44.71; H, 2.68; N, 1.24. IR (KBr pellet): vs(C=C) 1380, vs(C=S) 1060 and 1020, vsCC-S) 920 em-I. UV Ivis Amax (nm) 465, 350 and 290.

Synthesis of [(CH3hTej[Ni(dmithl 8 [(CH3hTeh[Ni(dmit)2] (1 mmo!) was dissolved in

acetone (60 ml) and air was bubbled through the solution for one hour. The volume was then reduced to 30-35 ml by evaporation under reduced pressure. To this solution, was added methanol (30 ml) to give a black precipitate. The precipitate was filtered and washed with methanol. Drying under vacuo for one hour gave crystalline [(CH3hTe][Ni(dmith] ; yield, 71%. Anal. Found: C, 16.91; H, 2.1 ; Calcd. for

2346 INDIAN J CHEM, SEC A, SEPTEMBER 2003

C9H9TeNiS\O: C, 17.32; H, 1.45. IR (KBr pellet): vs(C=C) 1350, vs(C=S) 1060 and 1040, v.(C-S) 900 em-I. UV/vis Amax (nm) 463,346 and 289.

Synthesis of [(CH3hTeJ[Ni(dmthl 9 . The benzoyl ester of the ligand (2 mmol) was

reacted with sodium methoxide solution (7 ml, 2M). NiCh.6H20 (1 mmol in 20 ml methanol) was added to the above solution. After stirring for 30 min a methanolic solution of trimethyltelluronium chloride (2 mmol) was added. The black solid was removed by filtration, washed with methanol and dried under vacuum. The compound was recrystallised from 1: 1 acetone-isopropanol mixture; yield, 71 %. Anal. Found: C, 16.9; H, 1.19; Ca1cd. for C9H9TeNiS\O: C, 17.32; H, 1.45. IR (KBr pellet) vs(C=C) 1370, vs(C=S) 1050, vs(C-S) 950 em-I. UV/vis Amax (nm) 605,410 and 330.

The complexes of Cu and Pd were prepared following the same procedure using the appropriate chlorides. In the case of Pt, aqueous solution of potassium tetrachloroplatinate was used.

[(CH3hTeh[Cu(dmthl 10; yield, 74%. Anal. Found: C, 17.02; H, 1.81; Ca1cd. for C12HISTe2CuS\O: C, 17.98; H, 2.26. IR (KBr pellet) vs(C=C) 1370, vsCC=S) 1060, vs(C-S) 950 em-I. UV/vis Amax (nm) 489,408 and 323.

[(CH3hTeJ[Pd(dmthl 11; yield, 80%. Anal. Found: C, 16.74; H, 1.40; Ca1cd. for C9H9TePdS\O: C, 16.09; H, 1.35. IR (KBr pellet) vs(C=C) 1370, vs(C=S) 1040, vs(C-S) 940 em-I. UY/vis Amax (om) 410, 330 and 244.

[(CH3hTeJ[Pt(dmthl 12; yield, 68%. Anal. Found: C, 13 .70; H, 1.40; Calcd. for C9H9TePtS\O: C, 14.33; H, 1.19. IR (KBr pellet) vs(C=C) 1370, vs(C=S) 1060, vs(C-S) 970 em-I . UV/vis Amax (nm) 380, 362 and 320.

Synthesis of [Au( dmthl 13 The benzoyl ester of the ligand (1 mmol) was

dissolved in sodium ethoxide solution (7 ml, 2M) to give a deep red solution. After stirring for 10 min KAuCl4 (1 mmol in 20 ml methanol) was added. A brown solid precipitated out immediately. After filtration, the solid was washed with methanol and dried under vacuum. Recrystallization was from 1: 1 of acetone isopropanol mixture; yield 72%. Anal. Found C, 11.99; Ca1cd. for C6AuS\O: C, 12.22%. IR (KBr pellet) vs(C=C) 1420, vs(C=S) 1050, vs(C-S) 940 em-I. UV/vis Amax (nm) 445,386 and 300.

Synthesis of [PPNlo.dAu(dmithll 14 [PPN] [Au(dmit)Zl (7)(1 mmol) was dissolved in

acetonitrile (25 ml). To this was added an acetonitrile

solution of iodine (1 mmol). The solution was kept overnight in the fridge to get a black precipitate of [PPNlo.1[Au(dmit)z 11; yield 22%. Anal. Found: C, 15.04; H, 0.56; N, 0.28; Calcd.: C, 14.96; H, 0.38; N, 0.18% .

Complexes 15, 16, 17 and 18 were synthesized following the above procedure with appropriate starting materials.

[(CH3hTelo.2[Ni(dmithll 15: yield, 48%. Found: C, 13.36; H, 0.32; Calcd. C, 12.98; H, 0.29%.

[(CH3hTelo.2[Ni(dmthll 16: (yield, 51 %. Found: C, 13.05; H, 0.62; Ca1cd. C, 12.93; H, 0.29%.

[(CH3hTelo.2[Pd(dmthll 17: yield, 58%. Found: C, 12.80; H, 0.52; Ca1cd. C, 12.10; H, 0.27%.

[(CH3hTelo.dAu(dmithll 18: yield, 58%. Found: C, 10.38; H, 0.28; Ca1cd. C, 10.32; H, 0.12%.

Synthesis of o-thiobenzeneselenolate (tbi-) ligand 19 The o-thiobenzeneselenolato (tbs2-) ligand was

conveniently prepared from benzenethiol and elemental selenium. Benzenethiol was lithiated with n-butyllithium in the presence of TMEDA in hexane. Elemental selenium was added to the dilithiated species to give the ligand as an orange slurry24.

Synthesis of [(CH3hTeJ[Ni(tbshl 20 A methanolic solution of trimethyltelluronium

chloride (1 mmol in 30 rnl of methanol) was added to a solution of 1-lithioseleno-2-lithiothiobenzene (1 mmol) dissolved in methanol (10 ml) and stined for 2 h. A solution of NiCh6H20 (0.5 mmol in methanol 20 ml) was added to the above solution and stirred for additional 1 h. A precipitate which formed was collected by filtration and dried under vacuo; yield, 48%. Anal. Found: C, 29.88; H, 2.88; Calcd. for CIsH17TeNiS2Se2: C, 29.75; H, 2.83%. IR (KBr pellet) v(cm-I) 3010, 2980, 2960, 1520, 1490, 1380, 1240, 1160, 1090, 1040, 760, 690 and 660. UV/vis Amax

(nm) 379, 326 and 250. Complexes 21-27 were prepared by using the

procedure described above. [(CH3hTel[Cu(tbshl 21; yield, 58%. Anal. Found:

C, 29.88; H, 2.00; Ca1cd. for CIsH17TeCuS2Se2: C, 29.51; H, 2.81 %. IR (KBr pellet) v(cm-I) 3020,2980, 1580, 1550, 1480, 1330, 1310, 1200, 1160, 1090, 1040, 1010, 810, 760, 710, 700 and 660. UV/vis Amax

(nm) 406, 360 and 240. [(CH3hTeJ[Au(tbshl 22; yield, 61 %. Anal. Found:

C, 24.2; H, 2.28. Calcd. for CIsH17TeAuS2Se2: C, 24.22; H, 2.30. IR (KBr pellet) v(cm-I) 3020, 2980. 2900, 1660, 1480, 1430, 1380, 1310, 1250, )180,

KOCHURANI et al.: CRYSTAL STRUCTURE OF [PPN][Au(dmith].CH3CN 2347

1160, 1090, 1040, 890, 830, 760, and 670. UV/vis Amax (nm) 420, 310., and 231.

[(Bu,IV][Ni(tbsh123; yield, 53%. Anal. Found: C, 49.65; H, 7.26; N, 2.03%; Calcd. for C2sRwNNiS2Se2: C, 49.77; H, 6.56; N, 2.07%. IR (KBr pellet) v(cm-1) 3010, 2970, 2940, 1470, 1445, 1410, 1290, 1240, 1165, 1145, 1090, 1040, 955, 760 and 665. UV/vis Amax (nm) 377, 323 and 246.

[(Bu,IV)][Cu(tbsh124; yield, 55%. Anal. Found: C, 48.86; H, 6.83;N, 2.83; Calcd. for C2sRwNCuS2Se2: C, 49.44; H, 6.52; N, 2.06%. IR (KBr pellet) v(cm-1) 3020, 2985, 1575, ' 1550, 1485, 1460, 1325, 1200, 1160, 1085, 1040, 1010,815, 760, 710, 705 and 665.

[(Bu,IV)][Au(tbsh125; yield, 53%. Anal. Found: C, 41.37; H, 5.41; N, 1.72; Calcd. for C2sRwNAuS2Se2: C, 41.33; H, 5.45; N, 1.72%. IR (KBr pellet) v(cm-1) 3020, 2980, 2960, 1490, 1440, 1390, 1300, 1250, 1190, 1170, 1100, 1040, 900, 820, 770 and 670. UV/vis Amax (nm) 420,304 and 258.

[(Me3NH)][Ni(tbsh126; yield, 52%. Anal. Found: C, 36.89; H, 3.70;N, 2.88; Calcd. for ClsH1SNNiS2Se2: C, 36.69;H, 3.70; N, 2.85%. IR (KBr pellet) v(cm-1) 3010, 2980, 2940, 1480, 1440, 1410, 1290, 1240, 1160, 1140, 1090, 1040, 950, 760 and 660.UV/vis Am •• (nm) 379, 326 and 250.

[(Me3NH)][Au(tbshl 27; yield, 38%. Anal. Found: C, 28.93; H, 2.89;N, 2.25; Calcd. for CJSHISNAuS2Se2: C, 28.62; H, 2.88; N, 2.22%. IR (KEr pellet) v(cm-I) 3020, 2980, 2880, 1710, 1080, 1490, 1420, 1390, 1300, 1240, 1190, 1160, 1090, 1030, 890, 820, 760 and 660. UV/vis Amax (nm) 420, 350 and 243.

Physical measurements Elemental analysis was carried out using a Carlo

Erba 1106 analyzer. Infrared spectra in the range of 4000-600 cm-J were recorded on a Perkin-Elmer grating spectrometer model 681. The solid samples were examined as KBr pellets. UV -Vis spectra in acetonitrile solution was recorded with a Schimadzu UV -260 spectrometer. Cyclic voltammetric studies were performed on an EGG Princeton Applied Research potentiostat model 273. Measurements were carried out in acetonitrile containing tetrabutylammonium perchlorate as a supporting electrolyte, using a conventional cell consisting of two platinum wires as working and counter electrodes and an Ag/ AgCl electrode as a reference. ESR spectra were recorded on a Varian E-112 spectrometer. Electrical conduction measurements were made using a two-probe measurement technique on compressed pellets26.

Data collection for X-ray crystallography A single crystal was mounted on a glass fibre on an

Enraf-Nonius CAD-4 diffractometer, equipped with graphite monochromated Mo-Ka radiation (A = 0.71073 A), <.0-28 scans. The structures were solved by Patterson method followed by weighted Fourier synthesis and refined by full-matrix least-square method. Structure determination package Enraf­Nonius3o on a V AX 11/750 computer was used for all calculations and PLUTO drawings31.

X-ray crystal structure determination of [PPNl [Au( dmith]. CH3CN

Crystal structure formula C44H33AuN2P2S 10, M = 1169.33, crystallizes as black plate-like crystals from acetonitrile by slow evaporation, triclinic space group, PI, a = 12.3859(10) A, b = 13.4097(10) A, c =

15.7789(10) A, a = 108.269(1)°, ~ = 97.15(1)°, Y = 99.82(1)°, V = 2407.6(3) A3, T = 293(2) K, Z = 2, Jl = 3.585 mm-1, 6377 unique reflections collected with 2.08<8<24.98°, R(int) = 0.0484. Refinement method: Full-matrix least-squres on F2, Final R indices [I>2cr(I)]: Rl = 0.0497, wR2 = 0.1170, R (all data): R, = 0.0484, WR2 = 0.1169.

Results and Discussion The synthetic pathways for the compounds in this .

study are presented in Scheme 1.

{

I. M= Ni, n&2, 1. M=Cu, n - 2} 3.M-Pd,n= I, 4.M=Pt.n"2 Cation"" 5.M~Au.n.:c 1 Mc)Te

(,.M=Cu.n=-2 ,.M - AU,D - I} Cation-PPN

• . S 5

/ S l.M" / "" /

[ 5] )X.'~' [ ~"'l. )X./".X>

s·

CX 1.M"

I 2. (Cotion)' # . Mctbmol

9. M - Ni. n-l, 10. M-Cu. n - 2 1l.M'"'Pd.o " I, 11. M-Pt,n-1

[lcc3.M:n-:"" /SoY'tll

[ ~ion 1 I # So/M""sNJ 10. M = Ni, 11. M::z Cu,21. M-Au. Cat.= Me3Te 13. M-Ni, 14. M - Cu.lS. :\i= Au, Cat"" Ilu .. N

16. M = Ni, 27. M - Au, Cat - Mc3NH

Scheme I-Synthetic routes for the preparation of the metal complexes

2348 INDIAN J CHEM, SEC A, SEPTEMBER 2003

Synthesis and characterization of {M(dmit hr-complexes

Disodium salt of dmit ligand was treated with metal chlorides (M = Ni, Pd, Pt, Cu, and Au) followed by the addition of a methanolic solution of (CH3)3Te+Cr or PPN+Cr yielded the new metal complexes (1-7). Ni, Pt and Cu complexes form dianionic salts, whereas Au and Pd complexes form monoanionic salts. Complex 8 was prepared from 1 by aerial oxidation of its acetone solution.

X-ray crystal structure of {PPN]{Au(dmithl.MeCN (7)

The molecular structure of [PPN][Au(dmith].MeCN (7) was confirmed from its single X-ray crystal structure. The PLUTON view of the molecular structure of complex (7) is shown in Fig. 1. The pertinent bond lengths and bond angles are presented in Table 1. The geometry around the Au is square planar. The complex [PPN][Au(dmith] crystallizes along with highly disordered solvent molecule in the triclinic space group PI. The packing of the anion is in the form of dimers with ap

interplanar distances of 6.129 A with the PPN+ cation on either side of the dimeric packing and none between the Au(dmith dimers (Fig. 2). Au ... S distance are in the range of 2.319(2)-2.327(2) A and are in good agreement with the previously reported bis(dithiolato)gold(IIl) complexes in (PCIPh3][Au[(S2C2(CF,hh] [2.288 A]32, [AU(S2CNBu"2hh(Au[S2C2(CNhh][2.309 A]33, [NBu"4][Au(S2C6H3Meh][2.322 A]34 and [NBu"4][Au(C3S5)2][2.322 A]35. The S-Au-S angles

~~::it, , ", . ........ - - rl :

I\1 J.:

Fig. I-PLUTON view of [PPNJ[Au(dmith] 7

91.6(8)° and 88.69(8)° are also close to the values reported for the related complexes. The packing between the two anions is very loose as interplanar distance between the two layer is 6.219 A. The cation PPN+ is not linear and exists in a bend configuration with a P-N-P angle of 138.9(5)°.

The packing of the anions in [PPN][Au(dmith] is in the form of dimers with interplanar distances of 6.129 A whereas in [(CH3hTe][Au(dmith]21, anions form a layer structure with an interplanar distance of 3.498 A. The shortest Au-S distance of [(CH3hTe][Au(dmith] is 2.309 A but for 7 the shortest Au-S distance is 2.319 A. The maximum deviation S-Au-S from ideal value is 1.32° for 7 and 1.9° for [(CH3h Te][Au(dmit)2]. The intermolecular S ... S distances change significantly with the increase in the size of the cation. The shortest intermolecular S ... S contact observed for 7 is 3.3333 A. In the case

Table I-Important bond lengths (A) and bond angles (0) of [PPN][Au(dmith] 7

Au(J)-S(I) 2.323(2) Au(I)-S(5) 2.327(2)

Au(1)-S(6) 2.320(2) Au( I)-S(l 0) 2.319(2)

P(l)-N(l) 1.576(8) P(2)-N(l) 1.589(7)

S( IO)-Au( 1)-S(6) 91.26(8) S(lO)-Au(l)-S(l ) 88.69(8)

S(6)-Au(l)-S(5) 88.68(8) S(I)-Au(l)-S(5) 91.38(8)

S(6)-Au(l)-S(I) 179.44(9) S(l O)-Au(l )-S(5) 178.96(9)

P( J )-N(l )-P(2) 138.9(5)

Fig. 2-Packing diagram of [PPN][Au(dmith] 7

KOCHURANI et al.: CRYSTAL STRUCTURE OF [PPN][Au(dmith].CH3CN 2349

of [(CH3hTeHAu(dmit)2] the shortest S ... S contact is 3.217 A. However, there are no considerable intermolecular S . .. S contacts in the complex [PPN][Au(dmit)2]. The cation PPN+ in both the complexes [PPN][Au(dmith] and [PPNHNi(dmithf2

are not linear and exist in a bent configuration. However, P~N-P bond angle of [PPN][Au(dmit)2] is much deviated from the nickel complex. The P-N-P bond angle for [PPN][Au(dmit)2] is 138.9(5)°, whereas for [PPN)[Ni(dmit)2] is 155.2(4)°.

Electronic spectra of dmit complexes were recorded in acetonitrile. M( dmit)2 n- complexes generally exhibit three well separated bands in the UV -Vis spectrum, the highest energy and lowest energy bands are due to 1t-1t* transitions of the ligand and the M f- S charge transfer (CT) transitions occur at the center35. In case of complex 7, CT transition was accompanied by a shoulder at lower energy due to a second CT transition.

For Ni and Au complexes, cyclic voltammograms showed two peaks each vs AgI AgCI that correspond to the following redox processes.

E1I2 = 0.25 V E1I2 = -0.1 V

+e- +e-. -2 [Au(dmith]O ~[Au(dmithrl~ [Au(dInlt)2]

-e- -e

E1I2 = 0.28 V EI/2 = -0.68V

In both complexes one peak is reversible and that corresponds to the [M(dmithrI/M(dmithr2 redox couple and second one, quasi-reversible that corresponds to the [M(dmithrIIM(dmith]o redox couple. The cyclic voltammogram of [PPNHCu(dmith] consists of two irreversible peaks whereas [(CH3hTe] [Pd(dmith] showed only one reversible peak.

Powder ESR studies were performed at room temperature and 77 K. The dianionic complexes except that of Cu and Au showed an isotropic signal at g = 2.02 due to the presence of free electron located on the thiolate ligand. [(CH3hTeHPt(dmit)2] gave an anisotropic signal accompanied by satellites at higher fields due to hyperfine splitting e95pt coupling). The principle 'g' values determined for the powder ESR · spectrum are found to be gl = 2.16, g2 = 2.06, g3 = 1.89 with hyperfine coupling constants are Al = 85

gauss and A2 = 90 gauss. The partially oxidized complexes showed stronger ESR signals compared to the monoanionic complexes. The 'g' values of both dmt and dmit complexes were around 2.01 - 2.04. The signals were due to the oxidized (C3Sd- species which occur around 2.01 - 2.04.

Synthesis and characterization of [M(dmthr­complexes

Similar reactions of benzoyl ester of dmt with metal chlorides (M = Ni, Pd, Pt, and Cu) in methanol followed by the addition of trimethyltelluronium chloride yielded products 9 to 12. All these chelates were dianionic in nature. Recrystallisation from hot acetone-isopropanol mixture changed the stoichiometry of dianionic salts and only Cu gave a dianionic species after recrystallization. This is probably due to aerial oxidation of the dianionic complexes to the monoanionic complexes during recrystallization. Surprisingly, the reaction of salt of dmt with KAuC4 gave a neutral species (13).

Electronic spectra of dmt complexes were recorded in acetonitrile. As expected, dmt complexes showed three well separated peaks.

While the [Au(dmthr1/[Au(dmthr2 redox process is observed as essentially a redox wave at -0.64 V vs Ag/AgCI, the [Au(dmth]ol [Au(dmthr1 process occurs irreversibly. Both the redox processes of [Au(dmth] species were observed at lower potential than that of [Au(dmithr species.

Oxidation of mono anionic complexes of dmit and dmt with iodine in acetonitrile gave the partially oxidized salts 14 to 18.

Synthesis and characterization of [M( tbs h],,-complexes

The o-thiobenzeneselenolate (tbs2-) ligand (19) is conveniently prepared by 'one pot' synthesis by following the procedure reported previously by our group24. Although several other methods are available to prepare tbs2- ligand36, our method takes the advantage of direct route. The methanolic solution of tbs2

- ligand was further reacted with the chlorides of nickel, copper and gold to obtain the corresponding complexes. The complexes 20 to 27 crystallized in good yields as tetrabutylammonium, trimethyl­ammonium and trimethyltelluronium salts.

The complexes exhibit complex electronic spectra which agree reasonably well with those of the corresponding bis(dithiolates) and bis(diselenol­ates)23c.38. The complexes generally show three

2350 INDIAN] CHEM, SEC A, SEPTEMBER 2003

absorption bands in UV spectra. The salient features of the absorption spectrum of [Me3NH][Ni(tbs)21 are as follows: The bands observemd at 379 nm and 250 nm are due to the intra ligand transitions. The band observed at 326 nm may be due to the LMCT transition. For [Me3Te][Ni(tbshl, the bands were observed at 380,323 and 248 nm respectively. Au and Cu complexes also showed a similar pattern. For the Au complex, first ligand transition was observed at 420 nm. As observed in the case of dithiolene37, most of the monoanionic complexes of tbs do not show appreciable ligand interaction, as judged by the consistency of their electronic spectra in a variety of solvents. The electronic spectra are almost unaltered when solvent is changed from dichlormethane to DMForDMSO.

As observed by Pleschner et al.23d , the cyclic voltammogram of [Ni(tbs)21 complexes showed two peaks. The first one is reversible and corresponds to the [Ni(tbshrl/[Ni(tbshr2 redox couple. The second one is irreversible and corresponds to the [Ni(tbshlo/[Ni(tbshr' redox couple. For tetrabutylammonium and trimethylarnmonium salts of [Ni(tbshl, [Ni(tbshr' I[Ni(tbshr2 process is observed at -0.52 V and -0.53 V vs SCE respectively. Cyclic voltammogram of [Bu4N][Cu(tbshl consists of two peaks, both [Cu(tbs)2r'/[Cu(tbshr2 (-0.86 V vs SCE) and [Cu(tbshlo/[Cu(tbshr' processes were irreversible. In the case of [Au(tbshrl complex the [Au(tbshrl/[Au(tbshr2 process was irreversible and [Au(tbshlo/[Au(tbs)X I process was quasi-reversible.

Electron Spin Resonance Spectra of [Me3NH][Ni(tbs)1 was recorded at 77 K in dimethylformamide-chloroform 'glass'. Fig. 3 shows three well separated principle g values: gl = 2.02, 82 = 2.07, g3 = 2.21 and <g> = 2.10. For [Ni(bdthr: g I = 2.02, g2 = 2.10, g3 = 2.12 and <g> = 2.08 and [Ni(bdshl-: gl = 2.07, g2 = 2.17, 83 = 2.17 and <g> = 2.1438. The increase in g-tensor anisotropy by substituting sulphur by selenium, apparently results from the greater spin-orbit coupling of the heavier donor atoms. Hyperfine splitting due to natural abundance of 77Se (7.5%, I = Vl) is observed on the high field resonance with a hyperfine coupling constant Al = 60 gauss. The low field resonance indicates the possible presence of unresolved 77Se hyperfine structure. However, since the hyperfine splitting was apparently not observed in the Ni[Se2C2(CF3hh - spectrum39, it is possible that both cis- and trans-isomers of [Ni(tbs)2r exist in the 'glass' with only g3 differing very significantly

-1 o 2 H-

Fig. 3-ESR spectrum of [Me3NH][Ni(tbs)2] (26) in 'DMF­CHCI3 Glass ' .

Table 2-Room temperature conductivity of the complexes

Complex

[PPN]ol[Au(dmit)2I] 14

[(CH3)3 Te]dNi(dmith I] 15

[(CH3hTe]O.1[Au(dmith lJ 18

[(CH3hTe]o.2[Ni(dmt)2 lJ 16

[(CH3)3Te]O.2[Pd(dmth lJ 17

Room temperature conductivity (0 Scm- I)

. 1.20x lO-3

6.80xlO-2

8.90x lO-4

1.24x lO-5

l.30x lO-5

between the two isomers. The resonance observed at the lowest field may be assigned to the cis-isomer, g:; (cis) = 2.22 (greater the distortions in the molecule. greater will be the anisotropy of the ESR spectrum); g3 (trans) was found to be 2.21. Ratios of the cis- and trans-isomers in the mixture were calculated from the intensities of the signals and were found to be 45.83% and 54.17% respectively.

The electrical conductivities of all complexes . were measured for a compacted pellet at room temperature. Only partially oxidized complexes showed noticeable room temperature conductivity (Table 2).

Conclusion The synthesis and characterization of several metal

complexes with various cations has been reported here and also three of them structurally characterized. The crystallographic studies prove that the change of central metal ions and the size of the cations play a crucial role in determining the crystal structure and

KOCHURANI et al.: CRYSTAL STRUCTURE OF [PPN][Au(dmith],CH3CN 2351

hence the physical properties. For example, the packing of the anions in [PPN][Au(dmith] is in the form of loose dimers with interplanar distances of 6.129 A whereas in [(CH3hTe][Au(dmith]21, anions form a layer structure with an interplanar distances of 3.498 A, where the cations are different. The P-N-P bond angle for [PPN][Au(dmith] is 138.9(5)°, whereas for [PPN][Ni(dmith] is 155.2(4)° where the metal atoms are different. All the monoionic and dianionic complexes were insulators. The partially oxidized complexes, however, showed much higher conductivities. Trimethyltelluronium salts of [Au(dmith] and [Ni(dmit)21 were found to be better conducting than the corresponding PPN analogues. Similarly, dmit complexes showed better conductivity than the corresponding dmt analogues.

Acknowledgement We are very thankful to Prof. P T Manoharan for

helpful discussions. Also thanks are due to DST and BRNS for financial support.

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