Mn^II, Cu^II and Co^II coordination polymers showing antiferromagnetism, and the coexistence of spin frustration and long range magnetic ordering

Based on the ligand 1,2-H₂bdc (1,2-H₂bdc = 1,2-benzenedicarboxylic acid), three 2D coordination polymers [Mn(1,2-bdc)] _n (1), [Cu(1,2-bdc)]_n (2) and [Co₃(OH) ₂(1,2-bdc)₂]_n (3), have been prepared and characterized. In comparison with the mononuclear Mn unit of compound 1, paddle-wheel binuclear Cu₂(CO₂)₄ and trinuclear Co₃(OH) building units are observed in 2 and 3, respectively. Also, the bdc^2- ligands adopt different coordination modes in the three compounds. The resulting two frustrated lattices have been observed, such as the triangular lattice for 2 and the Kagomé lattice for 3, and thus, both complexes 2 and 3 show spin frustrated antiferromagnetic properties. In addition, the magnetic hysteresis loops reveal the existence of the long range ordering in 2 and 3. Comparatively, the magnetic measurements indicate that compound 1 exhibits a weak antiferromagnetic interaction, and the fit of the variable-temperature magnetic susceptibility data to the empirical equation leads to the following parameters: J = -0.80(1) cm^-1 and g = 2.02.