Systematic studies of the structures and magnetic properties for a family of cubane complexes with the formula: [M2Ln2] (Ln = Dy, Gd; M = Ni, Zn) and [Ni2Y2]

Abstract

Studies of magnetic properties of a family of tetranuclear M^II₂Ln^III₂ (M = Ni, Zn; Ln = Dy, Gd and Y) complexes with hmp (anion of 2-hydroxymethylpyridine) and benzoate as ligands are reported. In these complexes, metal ions (M or Ln) occupy the four alternative corners of a distorted cubane with oxygen atoms from alkoxyl groups on the others. Complexes 1, 2 and 3 crystallized in P2₁/c and complexes 4 and 5 in C2/c space groups. Although in different space groups, complexes 1–5 have very similar structures which permit the magnetic interactions to be systematically compared with respect to metal ion pairs. In complex 3 (Ni₂Y₂), clear ferromagnetic coupling between Ni^II ions can be seen, with: g = 2.16, S = 2, D = −0.95 cm⁻¹, J = +3.77 cm⁻¹ (or g = 2.20, S = 2, D = +1.51 cm⁻¹). In complex 5 (Zn₂Gd₂), a very weak antiferromagnetic coupling between the Gd^III ions was observed: g = 2.08, J = −0.05 cm⁻¹. Based on these data, we concluded that the decrease in χ_MT − T upon cooling for complex 2 (Zn₂Dy₂) might be partly due to antiferromagnetic coupling between Dy^III ions. The data from complex 4 (Ni₂Gd₂) were analyzed based on the preceding results and gave moderate ferromagnetic coupling between Ni^II and Gd^III with J = 0.26 cm⁻¹. A detailed study of magnetic properties of complex 1 (Ni₂Dy₂) was not possible, because of its strong orbital contributions from Dy^III ions. In addition, frequency-dependent out-of-phase signals were clearly observed for both complexes 1 and 2 which can be attributed to magnetoanisotropy contributions from Dy^III ions.