Structural Variation withinHeterometallic UranylHybrids Based on Flexible Alkyldiphosphonate Ligands.

Five novel zinc uranyldiphosphonates have been hydrothermallysynthesized by using a series of flexible diphosphonate ligands, includingethane-1,2-diyldiphosphonic acid (H4EDP), propane-1,3-diyldiphosphonicacid (H4PDP), and butane-1,4-diyldiphosphonic acid (H4BDP). Compound Zn(H2tib)(UO2)2(EDP)(HEDP)(H2EDP)0.5·3H2O(EDP-ZnU1, tib = 1,3,5-tri(1H-imidazol-1-yl)benzene)comprises dimeric U2O12unit condensed by twoUO7pentagonal bipyramids, which are further connectedby Zn-centered polyhedra and EDP ligands resulting in a 3-dimensionalframework. Compound [Zn(bipy)(H2O)](UO2)(PDP)(PDP-ZnU1, bipy = 2,2′-bipyridine) also featuresU2O12dimers and Zn-centered polyhedra, buta layered arrangement is formed. Different from that in PDP-ZnU1, the uranium exists in the form of UO6tetragonal bipyramidand is surrounded by four PDP ligands to generate the layered structureof Zn(bipy)(UO2)(PDP) (PDP-ZnU2). ZnO2N2tetrahedra are connected on both sides of thelayers. Both Zn2(phen)4(UO2)3(BDP)(HBDP)2·4H2O (BDP-ZnU1, phen = 1,10-phenanthroline) and Zn2(bipy)2(UO2)3(HBDP)2(H2BDP)2(BDP-ZnU2) contain U2O12dimers and UO6tetragonal bipyramids. In BDP-ZnU1, uranyl centers are bridged by BDP to form a 2-dimensional structure,on which Zn(phen)2are decorated. Whereas in BDP-ZnU2, uranyl phosphonate layers are connected by bridging ZnO3N2to produce framework structure. All of these compoundshave been investigated by IR and photoluminescent spectroscopy. Theircharacteristic green light emissions have been attributed to transitionproperties of uranyl dications. [ABSTRACT FROM AUTHOR]