SYNTHESIS AND CHARACTERIZATION OF TETRAETHYLAMMONIUM AND 1,4-DIMETHYLPYRIDINIUM ANTIMONY(III) BIS-DMIT COMPLEXES

The synthesis and characterisation of two novel antimony (III) bis-dmi t complexes are reported [H-2-dmit = 4,5-dimercapto-1, 3-dithiole-2-th ione]. Compounds [Y][Sb(dmit)(2)] [Y = Et(4)N (1) and Y = C7H10N (1,4- dimethylpyridinium) (2)] are the first main group dmit complexes to sh ow significant metal-sulfur interanionic interaction in the solid stat e. The [Sb(dmit)(2)](-) anions in both complexes contain strong Sb-S p rimary bonds arranged to give pseudo trigonal bipyramidal antimony ato ms (lone pair of electrons in equatorial site; axial (Sb-S) mean 2.67 Angstrom and equatorial (Sb-S) mean = 2.50 Angstrom). Secondary Sb- - -S interanionic interactions have been revealed by X-ray crystallograp hy. Details of the crystal structures are as follows 1, monoclinic, C2 /c, a = 12.391(7) Angstrom, b = 13.090(7) Angstrom, c 15.587(8) Angstr om, beta = 102.7(1)degrees, V = 2466.3 Angstrom(3), Z = 4; for 2, tric linic, P (1) over bar, a = 8.986(5) Angstrom, b = 10.983(6) Angstrom, c = 11.365(6) Angstrom, alpha = 87.1(1)degrees, beta = 74.3(2)degrees, gamma = 88.0(1)degrees, V = 1245.2 Angstrom(3), Z = 2. The crystal st ructure of 1 consists of a polymeric two dimensional network formed by the bridging of Sb atoms and terminal S atoms of adjacent molecules. In contrast, the crystal structure of 2 consists of anionic dimers, al though this structure also involves bridging between Sb atoms and term inal S atoms. In both cases the Sb- - -S interanionic distances are ab out 3.3 Angstrom, which is 0.6 Angstrom shorter than the sum of the va n der Waals radii of Sb and S. Cyclic voltammetry studies of 1 in dime thylformamide show an oxidation wave and an associated reduction wave. The large separation, 0.7 V, between these is indicative of an interv ening chemical reaction.