Ferromagnetic interactions through triple hydrogen bonds in the coordination polymers of α,α′-dihydroxy-bibenzyl-4,4′- dicarboxylate

Three transition metal coordination polymers with α,α′- dihydroxy-bibenzyl-4,4′-dicarboxylate (L) were synthesized, and structurally and magnetically characterized. The three compounds, formulated as [M(L)(H₂O)₄]·2H₂O (M = Co(ii), Mn(ii) and Ni(ii)), are isomorphic and consist of one-dimensional coordination chains formed by the dicarboxylate ligand bridging the metal ions using monodentate carboxylate groups. Intriguingly, the [M(COO)₂(H₂O) ₄] spheres from different coordination chains are linked through triple O-H⋯O bridges to give the rare hydrogen bonded chains with [M(O-H⋯O)₃M] helicate motifs, which represent good systems suitable for investigating the exchange coupling through hydrogen bonding. Magnetic studies on Ni(ii) and Co(ii) compounds reveal that the triple hydrogen bonding bridge transmits ferromagnetic coupling, with J = 3.46 cm^-1 for the Ni(ii) compound and J = 1.12 cm^-1 for the Co(ii) compound.