SYNTHESIS, MOLECULAR-STRUCTURE AND ELECTROCHEMICAL INVESTIGATION OF THE 1,2,5-THIADIAZOLE-3,4-DITHIOLATE-SUBSTITUTED COMPLEX CP-ASTERISK-RU(NO)(TDAS) - EVIDENCE FOR NITROSYL BENDING DURING REDUCTION

Treatment of disodium 1,2,5-thiadiazole-3,4-dithiol (Na(2)tdas) with t he cyclopentadienyl complex CpRu(NO)Cl-2 in MeOH gives the correspond ing 1,2,5-thiadiazole-3,4-dithiolate-substituted complex CpRu(NO)(tda s) in 61% yield. The product has been characterized in solution by IR and NMR (H-1 and C-13) spectroscopies, and the molecular structure of CpRu(NO)(tdas) has been established by X-ray diffraction analysis. Cp Ru(NO)(tdas) crystallizes in the monoclinic space group P2(1)/c with a=26.204(2), b=8.4915(6), c=14.2339(9) Angstrom, beta=90.739(5)degrees , V=3166.9(3) Angstrom(3) and Z=8. Full-matrix least-squares refinemen t yielded R=0.0338 for 3151 (I>3 sigma(I)) reflections. The redox prop erties of CpRu(NO)(tdas) were examined by cyclic and rotating disk el ectrode voltammetric techniques. Two electrochemical responses were ob served and assigned to 0/+1 and 0/-1 redox couples. Both of these redo x couples are quasi-reversible. It is suggested that the stability of the 0/-1 redox couple is modulated by an EC scheme, whereby the initia l reduction product [CpRu(NO)(tdas)](.-) undergoes a bending of the n itrosyl ligand. The nitrosyl bending is observable at low temperature in THF solvent. The nature of the HOMO and LUMO levels in CpRu(NO)(td as) has been determined by extended Huckel molecular orbital calculati ons, the results of which are discussed with respect to the electroche mical data.