A rational design by hydrothermal methods of a tetrazolate-bridged bimetallic spin-canted antiferromagnet. Synthesis, X-ray structure and magnetic properties of [CoNi(pmtz)4] (Hpmtz− = 5-(pyrimidyl)tetrazole)

Abstract

The bimetallic complex [CoNi(pmzt)₄] (pmtz⁻ = 5-(pyrimidyl)tetrazolate ligand) has been prepared by hydrothermal treatment of an equimolecular mixture of the mononuclear complexes[Co(pmtz)₂(H₂O)₂] and [Ni(pmtz)₂(H₂O)₂]. The structure of [CoNi(pmzt)₄] consists of (4,4) square-grid-like sheets, in which Co(II) and Ni(II) metal ions are connected by pmtz⁻ bridging ligands. This compound is a spin-canted antiferromagnet (weak ferromagnet) with T_c = 18 K. Although Co(II) and Ni(II) ions have different spin values, the spin-canted structure can be formed because of the accidental compensation of their magnetic moments. Both magnetic anisotropy and antisymmetric exchange interaction promote the spin canting of the compensated magnetic moments in the 3D antiferromagnetic phase. On passing from the homometallic complex, [Co₂(pmzt)₄], which is also a spin-canted antiferromagnet with T_c = 15 K, to the bimetallic complex, [CoNi(pmzt)₄], T_c increases and the hysteresis parameters, remnant magnetization (M_r) and critical field (H_c), decrease. The increase in T_c may be a consequence of the increase of the J_CoNi, whereas the decrease in M_r and H_c is probably due to the presence in [CoNi(pmzt)₄] of a lower content of the highly anisotropic Co(II) ion