Ruthenium in isomeric S₄P₂ co-ordination: metal redox and geometrical reorganisation

The redox behaviour of dithiocarbonato complexes cis-[RuII(ROCS2)2(PPh3)2](1) has been electrochemically examined. One-electron oxidation affords cis-[RuIII(ROCS2)2(PPh3)2]+, (1+), which rapidly isomerises to the trans form, (2+). Electroreduction of (2+) furnishes trans-[Ru(ROCS2)2(PPh3)2], (2), which isomerises at a measurable rate to (1) probably by a twist mechanism (ΔS‡≈–110 J K–1 mol–1). The formal potentials of the couples (1+)–(1) and (2+)–(2) are respectively ≈0.7 and ≈0.3 V vs. saturated calomel electrode. The equilibrium constants for the reactions (1+)⇌(2+), (2)⇌(1), and (1+)+(2)⇌(2+)+(1) are respectively > 102, > 102, and ≈106. The cis and trans S4P2 co-ordination spheres are thus specific for bi- and tri-valent ruthenium respectively. The species (2+)(low-spin d5) display rhombic e.s.r. spectra in frozen solution (77 K). The rhombic crystal-field component (≈2 000 cm–1) is relatively small compared to the axial component (≈ 80000cm–1). An optical transition within Kramers doublets is observed at ≈6000 cm–1. One (2+) complex (R = PhCH2) has been isolated in the pure state as its PF6– salt