title: Magnetic anisotropy of mononuclear Ni(II) complexes: on the importance of structural diversity and the structural distortions.
abstract: Mononuclear Ni(II) complexes are particularly attractive in the area of single-molecule magnets as the axial zero-field splitting (D) for the Ni(II) complexes is in the range of -200 to +200 cm(-1) . Despite this advantage, very little is known on the origin of anisotropy across various coordination ligands, coordination numbers, and particularly what factors influence the D parameter in these complexes. To answer some of these questions, herein we have undertaken a detailed study of a series of mononuclear Ni(II) complexes with ab initio calculations. Our results demonstrate that three prominent spin-conserved low-lying d-d transitions contribute significantly to the D value. Variation in the sign and the magnitude of D values are found to correlate to the specific structural distortions. Apart from the metal-ligand bond lengths, two different parameters, namely, Δα and Δβ, which are correlated to the cis angles present in the coordination environment, are found to significantly influence the axial D values. Developed magneto-structural D correlations suggest that the D values can be enhanced significantly by fine tuning the structural distortion in the coordination environment. Calculations performed on a series of Ni(II) models with coordination numbers two to six unfold an interesting observation-the D parameter increases significantly upon a reduction in coordination number compared with a reference octahedral coordination. Besides, if high symmetry is maintained, even larger coordination numbers yield large D values.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay, Powai,Mumbai,Maharashtra,India-400 076, Fax: (+91) 22-2576-7152.
authors.forename: Saurabh Kumar
authors.initials: SK
authors.lastname: Singh
authors.forename: Tulika
authors.initials: T
authors.lastname: Gupta
authors.forename: Prashi
authors.initials: P
authors.lastname: Badkur
authors.forename: Gopalan
authors.initials: G
authors.lastname: Rajaraman
keywords: CASSCF calculations; magnetic anisotropy; magneto-structural correlations; nickel; zero-field splitting