Cobalt(II) phosphine complexes stable in aqueous solution: spectroscopic and kinetic evidence for low-spin Co(II)P 6 and Co(II)P 3S 3 with tripodal 1,1,1-tris(dimethylphosphinomethyl)ethane

Abstract

Co(II) species produced by the controlled potential electrochemical reduction of Co(III)P 3S 3 and Co(III)P 6 complexes with 1,4,7-trithiacyclononane and tripodal 1,1,1-tris(dimethylphosphinomethyl)ethane in aqueous solution were characterized at ambient temperature by the EPR and spectrophotometric methods: the Co(II)P 6 and Co(II)P 3S 3 species are in the low-spin t 2g 6e g 1 state with large Jahn–Teller distortion. Kinetic studies of the redox reactions involving these Co(III)/(II) species revealed that the electron self-exchange reactions for the Co(III)/(II) couples are very fast ( k ex∼10 4 dm 3 mol −1 s −1), which is consistent with the results for other low-spin/low-spin Co(III)/(II) couples. It was concluded that the nephelauxetic effect of the P donor atom stabilizes the low-spin state in Co(II).