SYNTHESIS AND SPECTROSCOPIC CHARACTERIZATION OF MIXED-FLUORO COMPLEXES OF UO22+ CONTAINING AMINO-ACIDS, ACETYLACETONATE OR ACETATE AS THE CO-LIGANDS AND THE 1ST REPORT ON THE HEPTAFLUORODIOXOURANATE(VI) COMPLEX [UO2F7]5-

The synthesis of mixed-ligand fluoro complexes of UO22+ of the types A3[UO2(GlyH)2F5].3H2O [A=K (1) or NH4+ (2)], K3[UO2(AlanH)2F5].2H2O (3), (NH4)5[UO2(CysH)2F5].2H2O (4), [UO2(acac)F(H2O)2].3H2O (6), K2[UO2(acac)F3] (8) and [UO2(CH3COO)F(H2O)2] (9) (GlyH = glycine, AlanH = alanine, CysH - = cysteinate and acac- = acetylacetonate) is described. The complexes have been characterized by a combination of chemical analyses, solution conductance measurements and spectroscopic studies. Vibrational spectroscopy has been used for their structural assessment. Laser Raman spectrum could be recorded only for K2[UO2(acac)F3] (8), while an extensive fluorescence foiled such attempts on the other complexes. Each of the three amino acid co-ligands acts in a unidentate manner, being coordinated to UO22+ through the caroxylate oxygen atom. While glycine and alanine occur in the zwitter-ionic form, cysteine seems to be present as a uninegative ligand. The reaction Of [UO2(acac)F(H2O)2].3H2O (6) with aqueous HF produced [UO2F2].3H2O (7). Treatment of K3[UO2(GlyH)2F5].3H2O (1) with water afforded the hitherto unreported potassium heptafluorodioxouranate(VI) dihydrate, K5[UO2F7].2H2O (5), in a high yield with satisfactory analysis and electrical conductance measurement (590 OMEGA-1 cm2 mol-1). IR and laser Raman spectra provide clear evidence for the presence of trans-linked O=U=O and coordinated flouride. The solution Raman spectrum of 5 is similar to that of its solid indicating that the structure in aqueous solution is the same as the solid. Scanning electron microscopy has been used to ascertain its homogeneity and crystalline nature.