Ruthenium dithiophosphates: synthesis, X-ray crystal structure, spectroscopic and electrochemical properties

The reactions of ammonium salts of dialkyldithiophosphate ligands, (RO)(2)P S2-NH4+ (R = Me/Et), with (RuCl3)-Cl-III . 3H(2)O in methanol solvent and u nder N-2 atmosphere result in one-electron paramagnetic tris complexes {(RO )(2)PS2}(3)Ru-III (1) in the solid state. The molecular structures of both complexes were determined by single-crystal X-ray diffraction. This shows t he expected pseudo-octahedral geometry with reasonable strain due to the pr esence of a four-membered chelate ring. The reflectance spectra of the soli d complexes display two bands in the range 596-476 nm and in the solid stat e the complexes exhibit one isotropic EPR signal at 77 K. Although the comp lexes 1 are stable in the solid state, in solution the complexes are transf ormed selectively into the diamagnetic and electrically non-conducting sulf ur-bridged dimetallic species [{(RO)(2)PS2}(2)RUIV (mu-S)(2)RUIV{S2P(OR)(2) }(2)]. The formation of dimeric species in the solution state is authentica ted by the electrospray mass spectrum of one representative complex where R = Et (1b). In dichloromethane solution the complexes show two moderately s trong sulfur to ruthenium charge-transfer transitions in the range 514-419 nm, and two strong ligand based transitions in the UV region. The complexes exhibit two successive reversible reductions in the ranges 1.01 --> 0.91 V and -0.44 --> -0.49 V versus SCE corresponding to Ru-IV-Ru-IV/Ru(III)Ru(II I)and (RuRuRuRuII)-Ru-III-Ru-III-Ru-II couples respectively. Electrochemica lly or chemically generated first step reduced complexes [{(RO)(2)PS2}(2)Ru -III (mu-S)(2)Ru-III{S2P(OR)(2)}(2)](2-) display two ligand to metal charge -transfer transitions in the visible region and in the complexes the two on e-electron paramagnetic metal centers (low-spin Ru-III, t(2g)(5),S = 1/2) a re antiferromagnetically coupled. The second step reduced species [{(RO)(2) PS2},Ru-II(mu-S)(2)Ru-II{S2P(OR)(2)}(2)](4-) are observed to be very unstab le. (C) 2000 Elsevier Science Ltd All rights reserved.