Carbon-substituted derivatives of [3,3'-Co(1-CH3-2-(CH2)(3)OR-1,2-C2B9H9)(2)](-) incorporating lipophilic ether chains (5, R = -CH2CH3; 6, R = -(CH2)(2)OCH3; 7, R = -(CH2)(3)CH3) have been synthesized. A procedure involving the simultaneous partial degradation and the ether formation ;on 1-CH3-2-(CH2)(3)Cl-1,2-C2B10H10 (1) has been developed. Extraction tests have been carried out for Cs-137, Sr-90, and Eu-152. Complex H[7] proved to have the best efficiency in the transport of Cs-137 at pH = 3 and an excellent selectivity in the presence of Sr-90 and Eu-152.