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