Functionalized cobalt bis(dicarbollide) ions as selective extraction reagents for removal of M2+ and M3+ cations from nuclear waste, crystal and molecular structures of the [8,8′-μ-CIP(O)(O)2(1,2-C2B9H10)2-3,3′-Co]HN(C2H5)3 and [8,8′-μ-Et2NP(O)(O)2(1,2-

New reliable synthetic methods leading to derivatives of the closo-[(1,2-C2B9H11)2-3,3′-Co]− (1) anion 1 with phosphorus containing substituents on the cage boron atoms have been successfully developed, starting from its 8-OH (2) and 8,8′-(OH)2 (3) hydroxyderivatives. Reactions of 2 with either Cl3PO or PhCl2PO followed by hydrolysis gave 8-(HO)2POO (4) and [(8-PhPO(OH)O)-1,2-C2B9H10)(1,2-C2B9H11)-3,3′-Co]− (5) phosphorylated species, respectively. Analogous reactions of Cl3PO with 3 provided a chlorine bearing bridged product [8,8′-μ-ClP(O)(O)2(1,2-C2B9H10)2-3,3′-Co]− (6) with surprisingly high hydrolytic stability. The anticipated anion [8,8′-μ-(HO)(O)-P(O)2(1,2-C2B9H10)2-3,3′-Co]− (7) with phosphoric acid as the bridging substituent was obtained after alkaline hydrolysis of compound 6. The related [8,8′-μ-Ph(O)P(O)2(1,2-C2B9H10)2-3,3′-Co]− (8) derivative was prepared by similar reaction of 3 with PhCl2PO and subsequent hydrolysis. Further developments starting from versatile precursor 6 led to synthesis of a derivative containing an asymmetric bridging diethylphosporamide moiety [8,8′-μ-(Et2N)P(O)(O)2(1,2-C2B9H10)2-3,3′-Co]− (9). A crystal of the compound 9 containing a pure enantiomer was selected, and its absolute configuration was determined by X-ray diffraction. Molecular structure of the compound 6 was also determined by X-ray diffraction analysis and the crystallographic results for both compounds are presented. Compounds 6 and 7 represent efficient Eu3+ extractants, enabling metal extraction even from highly acidic solutions (up to 1 M HNO3) to aromatic solvents. The novel compounds thus amalgamate in the single molecule good extraction properties of cobalta bis(dicarbollide) anion and the complexation ability of alkylphosphates.