Field-induced slow relaxation of magnetization in the S = 3/2 octahedral complexes trans-[Co{(OPPh2)(EPPh2)N}2(dmf)2], E = S, Se: effects of Co–Se vs. Co–S coordination

Abstract

The synthesis and the structural characterization of the octahedral trans-[Co{(OPPh₂)(EPPh₂)N}₂(dmf)₂], E = S (1), Se (2), complexes is described. These complexes are formed by crystallization of the corresponding tetrahedral [Co{(OPPh₂)(EPPh₂)N}₂] complexes in the presence of dimethylformamide (dmf) and are the first examples of intact octahedral Co(II) complexes bearing dichalcogenidoimidodiphosphinato ligands. X-ray crystallography studies revealed a trans-CoO₄E₂ first coordination sphere consisting of two chelating (OPPh₂)(EPPh₂)N⁻ ligands, as well as two dmf molecules coordinated via their O atoms. The isomorphous complexes 1 and 2 were studied by Direct Current magnetometry and shown to exhibit axial magnetic anisotropy. This finding was unequivocally confirmed by magnetic susceptibility measurements on an oriented crystal of complex 1, which clearly defined its easy axis of magnetization. Alternating Current magnetometry studies revealed field-induced slow relaxation of magnetization for both complexes, the characteristics of which are compared with those of other octahedral Co(II) complexes. The effects of the Se- vs. S-coordination on the magnetic anisotropy and relaxation properties of these and other 3d metal complexes are discussed.