Isoreticular 2D uranyl coordination polymers based on the mixed oxalate-succinate linkers

Two new oxalate-succinate uranium (VI) compounds with the guanidinium cations were synthesized and studied by single crystal X-ray diffraction, IR spectroscopy, thermogravimetric, and differential thermal analysis. The compounds are (CN3H6)(2)[(UO2)(2)(oxal)(suc)(2)]center dot 4H(2)O (1) and (CN3H6)(2)[(UO2)(2)(oxal)(2)(suc)]center dot 2H(2)O (2), where oxal = oxalate ion, C2O42- and suc = succinate ion, C4H4O42-. Crystal structures of both phases include 2D [(UO2)(2)(L)(3)](2-) complexes (L - dicarboxylate ion) with the same 'graphite sheet' topological type. However, the coordination numbers of uranium in the sheets are different for the different oxalate: succinate ratio in formula (2:1 or 1:2). The coordination number preference (8 or 7) was found to depend on the oxalate: U(VI) ratio.