Divalent and trivalent gas-phase coordination complexes of californium: evaluating the stability of Cf(ii)†
The divalent oxidation state is increasingly stable relative to the trivalent state for the later actinide elements, with californium the first actinide to exhibit divalent chemistry under moderate conditions. Although there is evidence for divalent Cf in solution and solid compounds, there are no reports of discrete complexes in which CfII is coordinated by anionic ligands. Described here is the divalent Cf methanesulfinate coordination complex, CfII(CH3SO2)3−, prepared in the gas phase by reductive elimination of CH3SO2 from CfIII(CH3SO2)4−. Comparison with synthesis of the corresponding Sm and Cm complexes reveals reduction of CfIII and SmIII, and no evidence for reduction of CmIII. This reflects the comparative 3+/2+ reduction potentials: Cf3+ (−1.60 V) ≈ Sm3+ (−1.55 V) ≫ Cm3+ (−3.7 V). Association of O2 to the divalent complexes is attributed to formation of superoxides, with recovery of the trivalent oxidation state. The new gas-phase chemistry of californium, now the heaviest element to have been studied in this manner, provides evidence for CfII coordination complexes and similar chemistry of Cf and Sm.