Crystal structures of uranyl complexes with isobutyrate and isovalerate anions.

Single crystals of Na[(UO2)(i-C3H7COO)3]·0.7H2O (I), Cs[(UO2)(i-C3H7COO)3] (II) and (NH4)[(UO2)(i-C4H9COO)3] (III) were obtained via isothermal evaporation and their structures were solved using X-ray diffraction techniques. Even though the ligands are branched, bulky and spatial, many carbon and hydrogen atoms are still disordered in these crystal structures at low temperature. A new type of Na coordination is observed for the first time for this family of compounds, proposing high sensitivity of compound I to humidity. Depolymerization of the metal-oxygen frameworks for the new compounds is compared with the known ones. Coordination sequences of sodium/cesium and uranyl complexes with aliphatic monocarboxylate ions are calculated to show different crystal-chemical function of crystallographically independent atoms. As there are analogous compounds to the title ones with straight-chain ligands, such groups of similar compounds with single varying parameters are very advantageous for establishing correlations between composition and crystal structure.