Uranyl-Organic Coordination Polymers with trans-1,2-, trans-1,4-, and cis-1,4-Cyclohexanedicarboxylates: Effects of Bulky PPh4+ and PPh3Me+ Counterions

Three uranyl ion complexes with trans-1,2-cyclohexanedicarboxylic acid (t-1,2-chdcH(2)) and six with trans- or cis-1,4-cyclohexanedicarboxylic acid (t- or c-1,4-chdcH(2)) have been obtained under solvo-hydrothermal conditions in the presence of PPh4+ or PPh3Me+ counterions. The complex [PPh4][UO2(R-t-1,2-chdc)(HCOO)] (1) crystallized on use of the pure (1R,2R) enantiomer of the dicarboxylate ligand, while the isomorphous complex [PPh4][UO2(S-t-1,2-chdc)(HCOO)] (2), containing the (1S,2S) enantiomer, resulted from use of the racemic form through spontaneous resolution. Both contain the rare diaxial (aa) form of the ligand and are one-dimensional (1D) polymers. The complex [PPh3Me][H2NMe2](3)[(UO2)(4)(R-t-1,2-chdc)(6)].H2O (3), with the pure enantiomeric, diequatorial (ee) form of the ligand, is a two-dimensional (2D) species with hnb topology, which derives from the structure of tetranuclear clusters previously reported. Complexes [PPh4][UO2(t-1,4-chdc)(NO3)].2CH(3)CN (4) and [PPh4][UO2(c-1,4-chdc)(NO3)] (5) are 1D polymers, helical in the latter case due to the axial-equatorial (ae) form of the ligand. [PPh4](2)[(UO2)(2)(t-1,4-chdc)(3)].4H(2)O (6), [PPh3Me](2)[(UO2)(2)(t-1,4-chdc)(3)].2H(2)O (7), [PPh3Me](2)[(UO2)(2)(c-1,4-chdc)(3)].2H(2)O (8), and [PPh4](2)[(UO2)(2)(t-1,4-chdc)(2)(c-1,4-chdc)].3H(2)O (9) all crystallize as 2D networks with honeycomb topology, the shape of the rings and that of the layers varying due to the presence of trans isomers in both the ee and aa forms, and coexistence of cis and trans isomers in 9; in all complexes 6-9, large channels are formed, which contain the counterions. The uranyl emission spectra of compounds 1-4, 6, and 9 in the solid state are in agreement with those usually found for tris-chelated carboxylate complexes, while that of complex 8, containing a mixture of seven- and eight-coordinate uranium atoms, displays a superposition of ill-resolved maxima within a broad envelope. A quantum yield of 0.13 was measured for complex 6.