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

Abstract

The reactions of ammonium salts of dialkyldithiophosphate ligands, (RO)₂PS₂^-NH₄⁺ (R=Me/Et), with Ru^IIICl₃.3H₂O in methanol solvent and under N₂ atmosphere result in one-electron paramagnetic tris complexes {(RO)₂PS₂}₃Ru^III (1) in the solid state. The molecular structures of both complexes were determined by single-crystal X-ray diffraction. This shows the expected pseudo-octahedral geometry with reasonable strain due to the presence of a four-membered chelate ring. The reflectance spectra of the solid complexes display two bands in the range 596-476 nm and in the solid state the complexes exhibit one isotropic EPR signal at 77 K. Although the complexes 1 are stable in the solid state, in solution the complexes are transformed selectively into the diamagnetic and electrically non-conducting sulfur-bridged dimetallic species [{(RO)₂PS₂}₂Ru^IV(μ-S)₂Ru^IV{S₂P(OR)₂}₂]. The formation of dimeric species in the solution state is authenticated by the electrospray mass spectrum of one representative complex where R=Et (1b). In dichloromethane solution the complexes show two moderately strong 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^III and Ru^III-Ru^III/Ru^II-Ru^II couples respectively. Electrochemically or chemically generated first step reduced complexes [{(RO)₂PS₂}₂Ru^III(μ-S)₂Ru^III{S₂P(OR)₂}₂]^2- display two ligand to metal charge-transfer transitions in the visible region and in the complexes the two one-electron paramagnetic metal centers (low-spin Ru^III, t_2g⁵, S=½) are antiferromagnetically coupled. The second step reduced species [{(RO)₂PS₂}₂Ru^II(μ-S)₂Ru^II{S₂P(OR)₂}₂]^4- are observed to be very unstable.