Structural and zeolitic features of a series of heterometallic supramolecular porous architectures based on tetrahedral {M(C2O4)4}4− primary building units

Abstract

The utilization of tetrahedral pre-formed coordination compounds {M(C₂O₄)₄}⁴⁻ (M = Zr^IV, U^IV; C₂O₄²⁻ = oxalate) permitted the efficient construction of rare examples of heteronuclear supramolecular nano-porous architectures. A series of metal–organic coordination frameworks prepared by association of these building units with either Mn²⁺, Cd²⁺, or Mg²⁺ have been structurally characterized and are described. Their 3-D chemical scaffold is based on the primary tetrahedral building unit but their pore sizes and topologies could be varied through the M²⁺ metal ion involved in the assembling process, and the anionic tetrahedral moiety. These structures display channels with apertures up to 12 Å × 8 Å which are emptied of solvates at mild temperatures without affecting the chemical scaffold, the integrity of which is maintained up to 250–300 °C. A certain degree of flexibility of the coordination polymers upon guest release is suggested by the temperature dependence of the powder X-ray patterns and N₂ sorption experiments, but reversible and selective sorption of small molecules has been observed substantiating that these open-frameworks behave like sponges.