LAUSR

Four isostructural MIII4LnIII2 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 MIII4DyIII2 (M = Fe or Ga) and FeIII4YIII2 analogues. DC magnetic susceptibility measurements for compounds 1–4, taken in combination with those for the FeIII4YIII2 analogue, indicated that the interactions between ErIII ions are weakly ferromagnetic and the FeIII–ErIII interactions are very weakly antiferromagnetic, while the HoIII–HoIII and FeIII–HoIII interactions are both negligible. By comparison, for the FeIII4DyIII2 analogue, the DyIII–DyIII interactions are antiferromagnetic while the FeIII–DyIII are ferromagnetic. Both Er analogues 1 and 2 display single-molecule magnet (SMM) behavior with the effective energy barrier Ueff 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.