Heterobimetallic Copper(II) Uranyl Carboxyphenylphosphonates

The hydrothermal reactions of uranyl nitrate with diethyl(2-ethoxycarbonylphenyl)phosphonate, 3-carboxyphenylphosphonic acid, or diethyl(3-ethoxycarbonylphenyl)phosphonate with HF result in the formation of [Cu(H2O)]2Cu(H2O)2[(UO2)(PO3C6H4CO2H)(PO3C6H4CO2)]2 (UCuCPPE-1) and [H3O]2[Cu(H2O)]2[(UO2)3(PO3C6H4CO2)4]·3H2O (UCuCPPE-2). UCuCPPE-1 is constructed from the UO2 2+ moiety coordinated by four additional oxygen donor atoms from the phosphonate moiety, resulting in a tetragonal bipyramidal geometry. The phosphonate groups span between the uranyl cations to create chains that are in turn linked into sheets by square planar and square pyramidal Cu(II) units. The phenyl groups separate the sheets from one another. The structure of UCuCPPE-2 consists of a three-dimensional network of tetragonal bipyramidal and pentagonal bipyramidal U(VI) centers. These units form chains that the phosphonate groups link into sheets. The sheets are then joined together by square pyramidal CuO5 units to create the three-dimensional network. In UCuCPPE-1, the phosphonate group coordinates to both uranium and copper, while the carboxylate moiety binds exclusively to the copper(II) centers. In contrast, the oxygen atoms from the phosphonate and carboxylate moieties in UCuCPPE-2 coordinate exclusively to the uranium and copper centers, respectively. Despite the presence of Cu(II) ions in these compounds, they both fluoresce, showing characteristic vibronically coupled charge-transfer based emission.