A Series of Novel Pentagonal-Bipyramidal Erbium(III) Complexes with Acyclic Chelating N(3)O(2) Schiff-Base Ligands: Synthesis, Structure, and Magnetism

A series of six seven-coordinate pentagonal-bipyramidal (PBP) erbium complexes, with acyclic pentadentate [N(3)O(2)] Schiff-base ligands, 2,6-diacetylpyridine bis-(4-methoxybenzoylhydrazone) [H(2)DAPMBH], or 2,6-diacethylpyridine bis(salicylhydrazone) [H(4)DAPS], and various apical ligands in different charge states were synthesized: [Er(DAPMBH)(C(2)H(5)OH)Cl] (1); [Er(DAPMBH)(H(2)O)Cl]·2C(2)H(5)OH (2); [Er(DAPMBH)(CH(3)OH)Cl] (3); [Er(DAPMBH)(CH(3)OH)(N(3))] (4); [(Et(3)H)N](+)[Er(H(2)DAPS)Cl(2)](−) (5); and [(Et(3)H)N](+)[Y(0).(95)Er(0).(05)(H(2)DAPS)Cl(2)](−) (6). The physicochemical properties, crystal structures, and the DC and AC magnetic properties of 1–6 were studied. The AC magnetic measurements revealed that most of Compounds 1–6 are field-induced single-molecule magnets, with estimated magnetization energy barriers, U(eff) ≈ 16–28 K. The experimental study of the magnetic properties was complemented by theoretical analysis based on ab initio and crystal field calculations. An experimental and theoretical study of the magnetism of 1–6 shows the subtle impact of the type and charge state of the axial ligands on the SMM properties of these complexes.