Thermal expansion behaviors of Mn(II)-pyridylbenzoate frameworks based on metal-carboxylate chains

Solvothermal reactions of MnCl2 with pyridylbenzoic acids gave three-dimensional metal-carboxylate frameworks (MCFs), named MCF-34, MCF-43, and MCF-44, based on one-dimensional Mn-carboxylate chains. The crystal structure, stability, porosity, and framework flexibility of the new compound MCF-44 were studied in detail and compared with its analogs. Depending on their shapes and the bridging angles of the ligands, these compounds possess different network connectivities and porosities. Considering the pyridylbenzote ligands and Mn(II) ions as, respectively, 3- and 6-connected nodes, they resemble either the anatase (ant) or rutile (rtl) polymorph of TiO2. Variable-temperature single-crystal X-ray diffraction studies revealed large thermal expansion coefficients for these compounds, which are probably related to the relatively flexible edge-sharing polyhedral structure of their Mn-carboxylate chains. Interestingly, the new compound MCF-44, with its highly porous rtl structure exhibits the largest thermal expansion coefficienct among the coordination polymers reported so far.