First Hexanuclear UIV and ThIV Formate Complexes – Structure and Stability Range in Aqueous Solution

The actinide(IV) hexanuclear [M 6 (μ 3 ‐O) 4 (μ 3 ‐OH) 4 (HCOO) 12 (L T ) 6 ] complexes were prepared (L T = H 2 O or CH 3 OH). Their structures were investigated by single‐crystal X‐ray analysis and XAFS spectroscopy. HCOO – acts as a bridging ligand, which prevents the formation of polynuclear hydrolysis species like U IV hydrous oxide colloids at least up to pH = 3.25, and stabilizes the nanosized clusters in solution. The charge of the hexamer is balanced by the O/OH ratio of the μ 3 ‐bridges.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)