Systematic studies of hexanuclear {M III4Ln III2} complexes (M = Fe, Ga; Ln = Er, Ho): structures, magnetic properties and SMM behavior

Abstract

Four isostructural M^III₄Ln^III₂ coordination clusters, [M₄Ln₂(μ₃-OH)₂(nbdea)₄(C₆H₅COO)₈]·MeCN (M = Fe, Ln = Er (1); M = Ga, Ln = Er (2); M = Fe, Ln = Ho (3); M = Ga, Ln = Ho (4)) have been synthesized and characterized. Single-crystal X-ray diffraction and X-ray powder diffraction studies revealed that all four compounds crystallize isomorphously to each other, and to the previously reported M^III₄Dy^III₂ (M = Fe or Ga) and Fe^III₄Y^III₂ analogues. DC magnetic susceptibility measurements for compounds 1–4, taken in combination with those for the Fe^III₄Y^III₂ analogue, indicated that the interactions between Er^III ions are weakly ferromagnetic and the Fe^III–Er^III interactions are very weakly antiferromagnetic, while the Ho^III–Ho^III and Fe^III–Ho^III interactions are both negligible. By comparison, for the Fe^III₄Dy^III₂ analogue, the Dy^III–Dy^III interactions are antiferromagnetic while the Fe^III–Dy^III are ferromagnetic. Both Er analogues 1 and 2 display single-molecule magnet (SMM) behavior with the effective energy barrier U_eff increasing from 12.8 K (for Fe₄Er₂1) to 53.5 K (for Ga₄Er₂2), indicating that the very weak 3d–4f interaction enhances the QTM effect.