Synthesis and characterization of dicarboranylmethylammonium polyoxometallates

Abstract

The reaction of [C2B10H11CH2NH3]Cl (3) with [NH4]6[Mo7O24][H2O]4 in water instantly afforded a white precipitate: crystallization from acetone–hexane thence gave the hybrid dicarborane octamolybdate salt, [C2B10H11CH2NH3]2[C2B10H11CH2NH=CMe2]2[Mo8O26][Me2CO]4.5 (5), whereas crystallization from acetonitrile–ether gave three further salts: [C2B10H11CH2NH3]2[C2B10H11CH2NH2CHMe2]2[Mo8O26][MeCN]2 (6), [C2B10H11CH2NH3]4[Mo8O26][MeCN]2[Et2O]2 (7) and [C2B10H11CH2NH3]2[C2B10H11CH2NH2Et]2[Mo8O26][MeCN]2 (8). Similarly, treatment of an acidified solution of Na2WO4 with [C2B10H11CH2NH3]Cl (3) in water also yielded a white precipitate: crystallization from acetone–hexane afforded the salt [C2B10H11CH2NH=CHMe2]4[W10O32][H2O]2[Me2CO]4 (10), whereas crystallization from acetonitrile–ether gave the double salt [C2B10H11CH2NH3]2[C5H5NH]2[W10O32][MeCN]2-[Et2O] (11). All these ‘globule–globule’ salts 5, 6, 8, 10 and 11 have been characterized by single-crystal X-ray diffraction analyses. Crystal structures reveal the presence of various small solvate molecules, together with an extensive network of hydrogen bonds between ammonium groups and oxygen atoms of the isopolyoxometallates. The isopropyl substituent in one of the carborane cations of the salts 6 and the ethyl substituent in one of the carborane cations of salts 8 may result from occluded isopropanol and ethanol in the starting salt 3 with alkylations of the primary ammonium group being assisted by isopolymolybdate anions. The presence of the pyridinium cation in 11 is believed to arise from contamination during work-up the reaction mixture.