Aromatic substituted metallacarboranes as extractants of 137Cs and 90Sr from nuclear wastes

Abstract

Phenyl- and 1,2-diphenyl-1,2-dicarba-closo-dodecaborane have been synthesized and deboronated to yield [7-C₆H₅-7,8-C₂B₉H₁₁]^– and [7,8-(C₆H₅)₂-7,8-C₂B₉H₁₀]^–. Reaction of the monophenyl with KOBu^t and CoCl₂ in 1,2-dimethoxyethane (dme) led to [3,3′-Co(1-C₆H₅-1,2-C₂B₉H₁₀)₂]^– 1^–. This has been fully characterized by X-ray analysis. A similar reaction with [7,8-(C₆H₅)₂-7,8-C₂B₉H₁₀]^– did not yield the expected sandwich compound. On the contrary, reaction of [7,9-(C₆H₅)₂-7,8-C₂B₉H₁₀]^– with KOBu^t and CoCl₂ in a mixture of dme and diethylene glycol dimethyl ether led to [3,3′-Co{1,7-(C₆H₅)₂-1,7-C₂B₉H₉}₂] 2^–. The two sandwich complexes were tested for liquid–liquid extraction and transport through supported liquid membranes of ¹³⁷Cs, ⁹⁰Sr and ¹⁵²Eu. Extractions for ¹³⁷Cs were very good at pH 3 but decreased considerably at pH 1 for H[1], while H[2] showed good efficiency even at this pH. The extraction of ⁹⁰Sr was performed with the incorporation of a synergistic linear polyether and was good at pH 3 and 1. For the extraction of ¹⁵²Eu, compound H[2] displayed good efficiency. Transport experiments of Cs using supported liquid membranes were performed with H[1] and H[2] and o-nitrophenyl hexyl ether as the membrane solvent. The permeability of ¹³⁷Cs for compound H[2] was 30.9 cm h^–1 while for H[1] it was 7.95 cm h^–1. These permeabilities are much higher than those of usual carriers under comparable conditions.