Structural Variations of the First Family of Heterometallic Uranyl Carboxyphosphinate Assemblies by Synergy between Carboxyphosphinate and Imidazole Ligands

Hydrothermal reactions of uranyl acetate and a series of transition metal acetates with a carboxyphosphinate and auxiliary N-donor ligands gave rise to the formation of eight heterometallic uranyl-organic assemblies, namely, Co­(im)₂(UO₂)₃(L)₄ (1), Zn­(bpi)­(UO₂)­(L)₂ (2), Cd­(dib)­(UO₂)­(L)₂ (3), M­(dib)­(UO₂)₂(L)₃ (M = Cd (4), Mn (5)), and [M­(dib)₂(H₂O)₂]­[(UO₂)₃(L)₄]·nH₂O (M = Co (6, n = 2), Ni (7, n = 2), Cu (8, n = 0)) [H₂L = (2-carboxyethyl)­(phenyl)­phosphinic acid (CPP), im = imidazole, bpi =1-(biphenyl-4-yl)-1H-imidazole, dib =1,4-di­(1H-imidazol-1-yl)­benzene]. Single-crystal X-ray diffraction (XRD) analysis of 1 reveals a layered structure of UO₆, UO₇, and CoO₄N₂ units that are linked by the carboxyphosphinate ligands. Imidazole molecules modify the layer by coordinating to Co centers. Similarly, 2 is a mixed zinc-uranyl carboxyphosphinate with different topological two-dimensional structure and the decorated moiety is a bpi coligand. When in the presence of bridging dib coligands, the mixed cadmium–uranyl carboxyphosphinate sheets of 3 are pillared by dib forming a framework structure. The isostructures of 4 and 5 are also pillared frameworks constructed by a mixed heterometallic uranyl phosphinate layered subnet that is different from that of 3. The structures of 6–8 are isotype and very special in that they consist of distinct [M­(dib)₂(H₂O)₂]_n²ⁿ⁺ cationic and [(UO₂)₃(L)₄]_n^2n– anionic subnets. Such two sheets are packed alternatively and interact via hydrogen bond forming three-dimensional supramolecular structures.