Cobalt(II) phosphine complexes stable in aqueous solution: spectroscopic and kinetic evidence for low-spin Co(II)P6 and Co(II)P3S3 with tripodal 1,1,1-tris(dimethylphosphinomethyl)ethane

Co(II) species produced by the controlled potential electrochemical reduction of Co(III)P3S3 and Co(III)P6 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)P6 and Co(II)P3S3 species are in the low-spin t2g6eg1 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 (kex∼104 dm3 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).