Synthesis of functionalized cobaltacarboranes based on the closo-[(1,2-C2B9H11)2-3,3′-Co]− ion bearing polydentate ligands for separation of M3+ cations from nuclear waste solutions. Electrochemical and liquid–liquid extraction study of selective transfer of M3+ metal cations to an organic phase. Molecular structure of the closo-[(8-(2-CH3OC6H4O)-(CH2CH2O)2-1,2-C2B9H10)-(1′,2′-C2B9H11)-3,3′-Co]Na determined by X-ray diffraction analysis