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 RuIIICl3·3H2O in methanol solvent and under N2 atmosphere result in one-electron paramagnetic tris complexes {(RO)2PS2}3RuIII (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}2RuIV(μ-S)2RuIV{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 RuIV–RuIV/RuIII–RuIII and RuIII–RuIII/RuII–RuII couples respectively. Electrochemically or chemically generated first step reduced complexes [{(RO)2PS2}2RuIII(μ-S)2RuIII{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 RuIII, t2g5, S=1/2) are antiferromagnetically coupled. The second step reduced species [{(RO)2PS2}2RuII(μ-S)2RuII{S2P(OR)2}2]4− are observed to be very unstable.