Unusual Heteronuclear Uranyl Clusters with Aliphatic Monocarboxylate Ligands and Coordination Modes of Crotonate, Butyrate, and Valerate Ions.

Two compounds with unusual architectures of uranyl complexes were synthesized and then studied by single‐crystal X‐ray diffraction and FTIR spectroscopy. Compound Ba2[UO2(C3H5COO)3]4·2C3H5COOH·7H2O (I) is constructed of neutral hexanuclear clusters {Ba2[UO2(C3H5COO)3]4(C3H5COOH)2(H2O)4} containing crotonate ions. Compound Sr(H2O)6{Na[UO2(i‐C3H7COO)3]3} (II) is constructed of anionic tetranuclear clusters {Na[UO2(i‐C3H7COO)3]3}2– containing isobutyrate ions. These and other examples of heteronuclear clusters imply that the alkali and alkaline‐earth metal atoms in these structures are not just charge‐balancing ions, but truly drive the formation of polynuclear units. The analysis of the coordination modes of crotonate, butyrate, and valerate ions in the crystal structures of all coordination compounds from the Cambridge Structural Database (CSD) allowed the identification of the structural role of these ligands. The results of the analysis show that the bridging function is in fact the most common function for crotonate, butyrate, and valerate ions in known crystal structures. Information on the possible and preferred coordination modes of ligands is extremely important for crystal structure prediction and crystal engineering. [ABSTRACT FROM AUTHOR]