Theoretical studies on magnetic interactions and charge-dope effects in one-dimensional Ni5 and Ni7 complexes

Abstract

Abstract The magnetic interactions between Ni(II) ions in one-dimensional complexes; [Ni5(tpda)4Cl2] and [Ni7(teptra)4Cl2] were examined by using theoretical calculations. Obtained spin densities were localized on Ni ions of both ends, therefore Ni ions of both ends were open-shell (S = 1) and inner Ni ions were closed-shell (S = 0). The calculated effective exchange integrals (Jab) between Ni ions of both ends were −12.6 and −6.4 cm−1 on [Ni5(tpda)4Cl2] and [Ni7(teptra)4Cl2], respectively and they reproduced experimental results well. Natural orbitals and their occupation number analyses explained their weak anti-ferromagnetic couplings that depended on their chain length and species of axial ligands. Their magnetic orbitals were σ and δ orbitals. The δ orbitals had completely localized structure, while σ orbitals were delocalized to axial ligands, suggesting that the axial ligands strongly affected the spin–spin interaction of electrons in σ orbitals. Negative orbital energies of LUMO and many unoccupied orbitals suggested the high electron affinities of those complexes. The model complex; [Ni5(tpda)4Cl2]2− was actually stable than [Ni5(tpda)4Cl2] about 1.5 eV. The electrons that were doped into bridge-ligand orbital did not disorder anti-ferromagnetic coupling in the complex. From the results, one of the candidates for the magnetic conductor seemed to be ‘δ-spin and ligand-conductor’ type structures by using such one-dimensional complexes.