High-frequency and -field EPR and FDMRS study of the [Fe(H 2O) 6] 2+ ion in ferrous fluorosilicate

Abstract

The complex [Fe(H 2O) 6]SiF 6 is one of the most stable and best characterized high-spin Fe(II) salts and as such, is a paradigm for the study of this important transition metal ion. We describe high-frequency and -field electron paramagnetic resonance studies of both pure [Fe(H 2O) 6]SiF 6 and [Zn(H 2O) 6]SiF 6 doped with 8% of Fe(II). In addition, frequency domain magnetic resonance spectroscopy was applied to these samples. High signal-to-noise, high resolution spectra were recorded which allowed an accurate determination of spin Hamiltonian parameters for Fe(II) in each of these two, related, environments. For pure [Fe(H 2O) 6]SiF 6, the following parameters were obtained: D = +11.95(1) cm −1, E = 0.658(4) cm −1, g = [2.099(4), 2.151(5), 1.997(3)], along with fourth-order zero-field splitting parameters: B 4 0 = 17 ( 1 ) × 10 - 4 cm - 1 and B 4 4 = 18 ( 4 ) × 10 - 4 cm - 1 , which are rarely obtainable by any technique. For the doped complex, D = +13.42(1) cm −1, E = 0.05(1) cm −1, g = [2.25(1), 2.22(1), 2.23(1)]. These parameters are in good agreement with those obtained using other techniques. Ligand-field theory was used to analyze the electronic absorption data for [Fe(H 2O) 6]SiF 6 and suggests that the ground state is 5A 1, which allows successful use of a spin Hamiltonian model. Density functional theory and unrestricted Hartree–Fock calculations were performed which, in the case of latter, reproduced the spin Hamiltonian parameters very well for the doped complex.