Alkaline Metal Fluoroxalatouranylates: Structure and Some Properties

Crystal structure Na3[UO2(C2O4)F3] · 4H2O (I), K3[UO2(C2O4)F3] (II), K3[UO2(C2O4)2F] · 3H2O (III) and Cs[UO2(C2O4)F] · H2O (IV) first studied by X-ray diffraction. Uranium–containing structural units are complexes [UO2(C2O4)F3]3ˉ (for I and II), [UO2(C2O4)2F]3- (III) and [UO2(C2O4)F]- (IV), accordingly with crystal chemical formulas А(В01)M13, А(В01)2M1 and А(Q02)M1, where A = UO22+, B01 or Q02 = C2O42-, and M1 = F- . In all compounds U(VI) atoms implement pentagonal-bipyramidal coordination, at that in I—III uranyl complexes have single–core structure, and in IV crystals–chain structure which is similar for the well — known for [UO2(C2O4)(H2O)] · 2H2O. The obtained results suggest that a sharp increase in the solubility of uranyl oxalate trihydrate in aqueous solutions with the addition of fluorides is due to the well-known effect of structural depolymerization of coordination polymers of d- or f-metals in the presence of fluoride ions. Semi-empirical calculation and comparison of calculated and experimental oscillation frequencies in IR spectra II and IV are carried out.