Simulation of change in conproportionation constants of the windmill complex [Cp3Co3(S6C6)]n− in the mixed-valence states (n = 1,2) by addition of crown ethers to solutions of alkaline metal ions

Abstract

Counterion size effects on the conproportionation constants K c1 and K c2 of the windmill complex [Cp 3 Co 3 (S 6 C 6 )](1)(Cp = η 5 -C 5 H 5 ) in the mixed-valence states 1 − and 1 2− respectively have been investigated electrochemically in solutions of alkaline metal ions and crown ether. Addition of 18-crown-6 (18C6) or 15-crown-5 (15C5) to a solution of 1 in NaBPII 4 δ THF brings enormous increases in both K c1 and K c2 at a concentration similar to that of NaBP 4 , and the change of K c2 is more significant than that of K c1 . This behaviour can be simulated using the complexation constants of crown ether with a cation obtained by conductivity analysis and several equations concerning association, ion pairing equilibrium, conproportionation and charge balance assuming that most of 1 − , 1 2− and 1 3− exist in the form of ion pairs.