Manganese(II) Pyrimidine-4,6-dicarboxylates: Synthetic, Structural, Magnetic, and Adsorption Insights

A series of manganese(II) coordination polymers containing the bridging ligand pyrimidine-4,6-dicarboxylate (pmdc) have been prepared. The stoichiometries and structural features of these materials, which range from the one-dimensional (1D) chains in (Mn(mu-pmdc)(H2O)3.2H2O)n (1) and (Mn2(mu-pmdc)2(H2O)5.2H2O)n (2) to the two-dimensional layers in (Mn(mu3-pmdc)(H2O).H2O)n (3) or the three-dimensional porous network in (Mn(pmdc).2H2O)n (4), are extremely dependent on the synthetic conditions (i.e., temperature and solvent). In spite of the structural diversity of these systems, crystallographic studies revealed that the pmdc ligand typically displays a tetradentate mu-(kappaO,kappaN:kappaO'',kappaN') coordination mode with the carboxylate groups almost coplanar with the pyrimidine ring as in compounds 1 and 2 and compound 5 described below). In compound 3, the pmdc moiety adopts a pentadentate mu3-(kappaO,kappaN:kappaO'',kappaN':kappaO) coordination mode. The thermal, magnetic, and adsorption properties of these systems were also studied. The results showed that these compounds behave as antiferromagnets as a consequence of efficient magnetic exchange through the pmdc bridges. Compound 4 possesses permanent porosity, as proved by gas sorption data (N2 at 77 K and CO2 at 293 K). Finally, the heteronuclear iron(II)/manganese(II) compound (FeMn(mu-pmdc)2(H2O)5.2H2O)n (5), which is isomorphous to 2, was also prepared and fully characterized.