Single-ion magnetism in seven-coordinate Yb^III complexes with distorted D_5h coordination geometry

Two seven-coordinate compounds with pentagonal bipyramidal Yb^III centers, namely, [Yb(H₃Bmshp)(DMF)₂Cl₂]·DMF·1.5H₂O (1) and [Yb(H₃Bmshp)(DMF)₂Cl₂]·H₄Bmshp (2) (H₄Bmshp = (2,6-bis[(3-methoxysalicylidene)hydrazinecarbonyl]-pyridine)) were synthesized by changing the molar ratio of reactants in DMF. The structures of compounds 1 and 2 are very similar, except for the existence of different lattice molecules: one DMF and one and a half water molecules in 1, and one neutral uncoordinated ligand in 2. The coordination geometries of both the pentagonal bipyramidal Yb^III centers (YbCl₂N₁O₄) in compounds 1 and 2 are also very similar with only slight differences. Magnetic data analyses revealed that the subtle structure variations result in remarkable different slow magnetic relaxation properties of compounds 1 and 2. To further understand their magnetic behaviors, ab initio calculations were performed for both compounds 1 and 2. The calculated results indicate that the magnetic anisotropies of compounds 1 and 2 are significantly different: easy-plane magnetic anisotropy for 1 and easy-axis magnetic anisotropy for 2. To the best of our knowledge, these compounds are the first Yb^III-based SIMs of pentagonal bipyramidal geometry.