A manganese(II) coordination polymer with mixed pyrimidine-2-carboxylate and oxalate bridges: Synthesis, structure, and magnetism

A new two-dimensional (2D) coordination polymer with mixed pyrimidine-2-carboxylate (pymca) and oxalate (ox) bridges, [Mn ₂(pymca)₂(ox)(H₂O)₂]_n (1), was synthesized by a hydrothermal reaction involving the in situ formation of the pymca and ox ligands from 2-cyanopyrimidine (pymCN), and its structure and magnetic properties were characterized. The dianionic ox and monoanionic pymca ligands are both potentially bis(chelating) and have been used to construct anionic and cationic 2D honeycomb networks [(6,3) net], respectively. In the present compound, ox assumes the usual bis(chelating) bridging mode, but pymca serves as a tridentate bridge with one of the pyrimidyl nitrogens uncoordinated. The two different bridges collaborate to generate a highly undulated 2D layer with the (6,3) net topology, and the layers are closely packed in parallel through π-π interactions between pyrimidyl rings and hydrogen bonds involving coordinated water molecules, oxalate oxygens, and uncoordinated pyrimidyl nitrogens. Magnetic measurements reveal that the compound is a spin-canted antiferromagnet with weak ferromagnetic transition below T_c = 2.4 K.