MONONUCLEAR DIOXOURANIUM(VI) AND THORIUM(IV) COMPLEXES WITH POTENTIALTETRADENTATE BRIDGING CHELATORS

The bi-heterocycle, 2,2'-biimidazole (H-2Biim) forms mononuclear compl exes of the type UO2(H2Biim)X2 (X = Cl, NCS); UO2(H2BiiM)2X2 (X = I, N O3, CH3COO, 0.5SO4) and Th(H2Biim)2X4 (X = 1, CNS, NO3). Further, the mixed-ligand complexes UO2(H2acacen) (H2Biim)X2 (X = Cl, NCS) and the hetero-bimetallic complex UO2(H2Biim) HgCl4 were also obtained and cha racterized on the basis of IR, electronic and H-1 NMR spectral evidenc e and thermogravimetric studies. The H-1 NMR spectrum of the free liga nd shows that the ring protons are equivalent and give rise to a sharp singlet at delta 6.92 ppm and at 13.13 ppm for the imine proton (-NH) . In the complexes, the two singlets at ca 7.8 and 8.5 ppm clearly con firm the inequivalence of the ring protons due to coordination of the biimidazole. The coordination also results in an upfield shift of the imine proton (-NH) signal from 13.13 to 3.5 ppm in the complexes. Alth ough uranyl salts are known to fluoresce, in these complexes the fluor escence seems to be quenched, ruling out the involvement of H2Biim in the emission decay process.