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 UO22+ 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.硝酸铀酰与二乙基(2-乙氧羰基苯基)膦酸酯、3-羧基苯基膦酸，或二乙基(3-乙氧羰基苯基)膦酸酯在氢氟酸（HF）中进行水热反应，制备得到[Cu(H₂O)]₂Cu(H₂O)₂[(UO₂)(PO₃C₆H₄CO₂H)(PO₃C₆H₄CO₂)]₂（命名为UCuCPPE-1）与[H₃O]₂[Cu(H₂O)]₂[(UO₂)₃(PO₃C₆H₄CO₂)₄]·3H₂O（命名为UCuCPPE-2）。 UCuCPPE-1由铀酰阳离子(uranyl cation, UO₂²⁺)与来自膦酸根基团(phosphonate moiety)的四个额外氧供体原子配位构建，呈现四方双锥几何构型。膦酸根基团桥连铀酰阳离子形成链状结构，随后通过平面正方形与四方锥构型的铜(II)单元将链状结构互连为层状结构；苯基基团则实现各层之间的空间分隔。 UCuCPPE-2的结构由四方双锥与五角双锥构型的六价铀(U(VI))中心构成三维网络。这些铀中心先形成链状结构，再经膦酸根基团连接为层状结构；后续通过四方锥构型的CuO₅单元将层状结构拼接，最终形成完整的三维网络。 在UCuCPPE-1中，膦酸根基团同时与铀和铜中心配位，而羧酸根基团(carboxylate moiety)仅与铜(II)中心结合。与之相对，UCuCPPE-2中的膦酸根基团与羧酸根基团的氧原子分别仅与铀中心和铜中心配位。 尽管这两种化合物中均含有铜(II)离子，但二者均表现出荧光发射特性，展现出典型的振动耦合电荷转移(vibronically coupled charge-transfer)基发射行为。