Magnetic ordering in organic transition-metal compounds

The magnetic properties of metalorganic compounds attract much attention as their structural and electronic exchange dimensionality can vary between one and three. Here, we present data of representatives which exhibit magnetic ordering and have been recently investigated by means of magnetometry and calorimetry. In the quasi-cubic compound [Cu(HF₂)(pyz)₂]BF₄, we have observed an antiferromagnetic (AF) ordered phase occurring at T_N = 1.6K and a rich magnetic phase diagram up to 14 T as well. Above T_N, the specific heat of that compound is in reasonable agreement with the predictions of the model for a s = 1/2 2D square lattice quantum Heisenberg AF describing the in-plane exchange via the Cu−F −H−F −Cu bonds. In the quasi- 1D compound Mn(glycine)(H₂O)₂Cl₂ which is structurally arranged in helical chains, we have observed an unexpected 3D AF ordering at T_N = 0.84 K, both in the results of the heat capacity and ac susceptibility. Probably, the 3D exchange is mediated by hydrogen bonds between the chains in addition to Mn−O−Mn bonds along the chains.