Abstract

A kind of molecule-based magnets, metal-assembled complexes tend to possess low-dimensionalities for their magnetic lattices. Heat capacity calorimetry is a powerful tool for elucidation of the magnetic properties of metal-assembled complexes. Heat capacity measurements were carried out for the one-dimensional metal-assembled complexes Mn^IICu^II(obbz).nH₂O (obbz = oxamidobis(benzoato), n = 1, 5) and two-dimensional metal-assembled complexes NBu₄[M^IICr^III(ox)₃] (Bu = n-butyl; M = Cu, Fe; ox = oxalato) and PPh₄[Mn^IICr^III(ox)₃] (Ph = phenyl). Mn^IICu^II(obbz).5H₂O undergoes an antiferromagnetic phase transition at T_N = 2.18 K and have a heat capacity hump above T_N, which can be reproduced well by the spin quantum number S = 2 one-dimensional ferromagnetic Heisenberg model with the intrachain exchange interaction J/k_B = 0.75 K, where k_B is the Boltzmann constant. Partially dehydrated Mn^IICu^II(obbz)H₂O exhibits a ferrimagnetic phase transition at T_c = 17 K and shows a heat capacity tail above T_c, which can be reproduced rather by the S = 2 two-dimensional ferromagnetic Heisenberg models. NBu₄[Cu^IICr^III(ox)₃], NBu₄[Fe^IICr^III(ox)₃], and PPh₄[MnCr(ox)₃] indicate ferromagnetic phase transitions at T_C = 6.98 K, 12.0 K, and 5.85 K, respectively, and heat capacity tails above T_C, which can be reproduced well by the two-dimensional ferromagnetic Heisenberg models of honeycomb lattice with the intralayer exchange interactions J/k_B = 5.0 K, 2.5 K, and 0.95 K, respectively.

Keywords: Heat capacity, high-temperature series expansion, magnetic entropy, magnetic phase transition, metal-assembled complex, molecule-based magnet, low dimensionality, spin wave.

Graphical Abstract