Maleate ions as ligands in crystal structures of coordination compounds, including two uranyl complexes

Abstract

Synthetic techniques, FTIR spectra and the crystal structures of two new uranyl complexes with maleate ions are reported. The crystal structure of (NH4)2[UO2(C4H2O4)2] (I) is constructed of chains with the [UO2(C4H2O4)2]2− composition. Maleate ions in I have the tridentate bridging and chelating T11-4 coordination mode with the formation of 4-membered U-containing rings. The crystal structure of Cs2[(UO2)3(C4H2O4)4]·2H2O (II) is constructed of layers with the [(UO2)3(C4H2O4)4]2− composition. Half of the maleate ions in II have the bridging and chelating Q21-4 coordination mode, with the formation of 4-membered rings, while the other half have the Q21-7 coordination mode with the formation of 7-membered rings. The coordination modes of the maleate ions in all the crystal structures of coordination compounds from the CSD were analyzed. The non-planarity of the maleate ions is confirmed by calculation of different geometric parameters. Though in all crystal structures most of the maleate ions tend to realize coordination modes with the formation of 7-membered rings, geometrical difficulties of 7-membered ring formation are shown. The presented data on the coordination modes of the maleate ions in crystal structures are of particular interest for crystal engineering and crystal structure prediction.