Synthesis, structures, and magnetic properties of three 3D coordination polymers based on M 4O 4 Cubanes (M = Mn II, Fe II, Co II)

Three new isostructural coordination polymers, namely, [M 4(μ 3-OMe) 4(nic) 4] n [M = Mn II (1), Fe II (2), and Co II (3); Hnic = nicotinic acid], have been solvothermally synthesized and magnetically characterized. Single-crystal X-ray diffraction study reveals that compounds 1-3 are three-dimensional frameworks, which are constructed through {M 4(μ 3-OMe) 4} cubane-like building blocks and bridging nic - anions. Variable-temperature magnetic susceptibility measurements indicate that they all show antiferromagnetic behavior with different intracubane coupling constants. Complex 1 exhibits spin-frustration behavior, and was fitted with a two-J model in the temperature range of 2-300 K, which gives J 1 = -0.92 and J 2 = -2.23 cm -1. Complexes 2 and 3 were fitted with the same model in the temperature range of 30-300 K and 40-300 K to give the exchange coupling constants J 1 = -2.49, J 2 = 4.84 cm -1 and J 1 = -4.18, J 2 = 5.44 cm -1, respectively. Three new isostructural coordination polymers constructed by M 4O 4 cubane cores (M = Mn II, Fe II, Co II) and nic - (Hnic = nicotinic acid) bridges have been synthesized and characterized. The manganese compound shows antiferromagnetic coupling between adjacent Mn II ions in the cubane, whereas the iron and cobalt compounds exhibit antiferromagnetic and ferromagnetic interactions within the cubanes. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.