Hepta-coordinated Ni(ii) assemblies – structure and magnetic studies

Abstract

Two mononuclear complexes [Ni(dapsc)(H₂O)₂]Cl(NO₃)·H₂O (1) and [Ni(dapsc)(NCS)₂] (2), and a bimetallic CN-bridged trinuclear molecule [Ni^II(dapsc)(H₂O)]₂[W^IV(CN)₈]·11H₂O (3) (dapsc = 2,6-diacetylpyridine-bis(semicarbazone)) were synthesised and characterised in terms of structure and magnetic properties. All three compounds contain Ni(II) ions in a pentagonal bipyramid coordination geometry afforded by the equatorial pentadentate ligand (dapsc) and two O- or N-donating axial ligands. The compounds differ in the relative arrangement of the complexes, intermolecular interactions and distortion from the ideal coordination geometry. The high-field EPR and magnetometric studies show large anisotropy of the Ni(II) centres with the D parameters in the range of −10.5 to −21.2 cm⁻¹ and negligible antiferromagnetic interactions. The easy-axis magnetic anisotropies of 1–3 were reproduced by ab initio CASSCF/NEVPT2 calculations. The ground states consist mainly of the |M_S〉 = |±1〉 states, which is consistent with the fact that no out-of-phase signal can be detected in the AC magnetic susceptibility measurements.