Novel manganese(II) and cobalt(II) 3D polymers with mixed cyanate and carboxylate bridges: crystal structure and magnetic properties

Two isomorphous 3D Mn(II) and Co(II) coordination polymers with a dicarboxylate inner salt and cyanate as coligands were synthesized and structurally characterized, and their magnetic properties have been studied. In the compounds, [M(L)(NCO)]_n·nH₂O (M = Mn, Co, L = 1-carboxymethylpyridinium-4-carboxylate), neighboring metal ions are linked by the 3-fold bridges of an end-on cyanate and two syn–syn carboxylate bridges to give an anionic chain of [M(µ-NCO)(µ–COO)₂]_n, and each chain is interlinked to four other chains by the cationic 1-methylpyridinium spacers to generate a 3D structure with the 4²· 6³· 8 net topology. They are the first compounds with mixed cyanate and carboxylate bridges. Magnetic studies reveal that the 3-fold mixed bridge propagates antiferromagnetic coupling in the Mn(II) compound but ferromagnetic coupling in the Co(II) compound. The rather complex magnetic behaviors of the Co(II) compound are analyzed taking into account the first-order spin-orbital coupling and the intrachain ferromagnetic interactions.