Synthesis of two-dimensional metal–organic networks from 1,10-phenanthroline-chelated cadmium complex and polycarboxylate

The design of two 2D metal–organic frameworks using a 1,10-phenanthroline-chelated cadmium complex as precursor and a bridging polycarboxylate as linker is described. The reaction of Cd(NO3)2·4H2O with the chelating ligand 1,10-phenanthroline (phen) at room temperature gave [Cd(phen)(NO3)2] (1) in high yield. Treatment of the inorganic precursor 1 with the polycarboxylate bridge ligand, benzene-1,4-dicarboxylic acid (H2BDC) or benzene-1,2,4,5-tetracarboxylic acid (H4btec), under mild hydrothermal conditions led to the formation of two metal–organic networks {[Cd(BDC)(phen)]·DMF}n (2) and [Cd2(btec)(phen)2]n (3). Single-crystal X-ray diffraction analyses showed that both products have two-dimensional sheet architectures. Compound 2 was constructed via the use of [Cd2(O2C)4] unit and BDC linker, whereas compound 3 involved the use of [CdO4] core and btec bridge. The cadmium ions in compounds 2 and 3 are hepta- and hexa-coordinated, respectively. Thermogravimetric (TG) analyses showed that 2 and 3 are thermally stable (Tdecomp. > 360 °C). Photoluminescence studies revealed that compounds 1–3 displayed a strong fluorescent emission in the solid state at room temperature.