Unraveling sigma and pi Effects on Magnetic Anisotropy in cis-NiA(4)B(2) Complexes: Magnetization, HF-HFEPR Studies, First-Principles Calculations, and Orbital Modeling

作者：Charron Gaelle; Malkin Elena; Rogez Guillaume; Batchelor Luke J; Mazerat Sandra; Guillot Regis; Guihery Nathalie; Barra Anne Laure; Mallah Talal^*; Bolvin Helene^*

来源：Chemistry - A European Journal, 2016, 22(47): 16848-16860.

DOI：10.1002/chem.201602837

• ab initio calculations
• EPR spectroscopy
• magnetic properties
• nickel
• quantum chemistry

By using complementary experimental techniques and first-principles theoretical calculations, magnetic anisotropy in a series of five hexacoordinated nickel(II) complexes possessing a symmetry close to C-2v, has been investigated. Four complexes have the general formula [Ni(bpy)X-2](n+) (bpy=2,2'-bipyridine; X-2=bpy (1), (NCS-)(2) (2), C2O42- (3), NO3- (4)). In the fifth complex, [Ni(HIM2-py)(2)(NO3)](+) (5; HIM2-py=2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-hydroxy), which was reported previously, the two bpy bidentate ligands were replaced by HIM2-py. Analysis of the high-field, high-frequency electronic paramagnetic resonance (HF-HFEPR) spectra and magnetization data leads to the determination of the spin Hamiltonian parameters. The D parameter, corresponding to the axial magnetic anisotropy, was negative (Ising type) for the five compounds and ranged from -1 to -10 cm(-1). First-principles SO-CASPT2 calculations have been performed to estimate these parameters and rationalize the experimental values. From calculations, the easy axis of magnetization is in two different directions for complexes 2 and 3, on one hand, and 4 and 5, on the other hand. A new method is proposed to calculate the g tensor for systems with S=1. The spin Hamiltonian parameters (D (axial), E (rhombic), and g(i)) are rationalized in terms of ordering of the 3d orbitals. According to this orbital model, it can be shown that 1) the large magnetic anisotropy of 4 and 5 arises from splitting of the e(g)-like orbitals and is due to the difference in the sigma-donor strength of NO3- and bpy or HIM2-py, whereas the difference in anisotropy between the two compounds is due to splitting of the t(2g)-like orbitals; and 2) the anisotropy of complexes 1-3 arises from the small splitting of the t(2g)-like orbitals. The direction of the anisotropy axis can be rationalized by the proposed orbital model.

• 出版日期2016-11