Pseudooctahedral Complexes of Vanadium(III):  Electronic Structure Investigation by Magnetic and Electronic Spectroscopy

Abstract

A variety of physical methods has been used to probe the non-Kramers, S = 1, V(III) ion in two types of pseudooctahedral complexes: V(acac)(3), where acac = anion of 2,4-pentanedione, and VX(3)(thf)(3), where thf = tetrahydrofuran and X = Cl and Br. These methods include tunable frequency and high-field electron paramagnetic resonance (HFEPR) spectroscopy (using frequencies of approximately 95-700 GHz and fields up to 25 T) in conjunction with electronic absorption, magnetic circular dichroism (MCD), and variable-temperature variable-field MCD (VTVH-MCD) spectroscopies. Variable-temperature magnetic susceptibility and field-dependent magnetization measurements were also performed. All measurements were conducted on complexes in the solid state (powder or mull samples). The field versus sub-THz wave quantum energy dependence of observed HFEPR resonances yielded the following spin Hamiltonian parameters for V(acac)(3): D = +7.470(1) cm(-1); E = +1.916(1) cm(-1); g(x) = 1.833(4); g(y) = 1.72(2); g(z) = 2.03(2). For VCl(3)(thf)(3), HFEPR detected a single zero-field transition at 15.8 cm(-1) (474 GHz), which was insufficient to determine the complete set of spin Hamiltonian parameters. For VBr(3)(thf)(3), however, a particularly rich data set was obtained using tunable-frequency HFEPR, and analysis of this data set gave the folowing: D = -16.162(6) cm(-1); E = -3.694(4) cm(-1); g(x) = 1.86(1); g(y) = 1.90(1); g(z) = 1.710(4). Analysis of the VTVH-MCD data gave spin Hamiltonian parameters in good agreement with those determined by HFEPR for both V(acac)(3) and VBr(3)(thf)(3) and in rough agreement with the estimate for VCl(3)(thf)(3) (D approximately 10 cm(-1), |E/D| approximately 0.18), together with the finding that the value of D is negative for both thf complexes. The electronic structures of these V(III) complexes are discussed in terms of their molecular structures and the electronic transitions observed by electronic absorption and MCD spectroscopies.

Electronic structure of V3+ in NaMgAl(ox)3·9H2O probed by Fourier transform spectroscopy

“…The trisoxalatovanadium (III) anion, [V(ox) 3 ] 3À , has received attention in recent years because of its application as a component in multi-nuclear, mixed-valence molecular magnets [1]. In order to understand the complex magnetic properties of these multi-component systems, the electronic structure of the mononuclear (paramagnetic) components needs thorough investigation, which is lacking for the [V(ox) 3 ] 3À anion.…”

“…Pseudooctahedral V 3+ has a 3 T 1g ground state that is difficult to study by classical electron resonance spectroscopy due to the large axial zero-field splitting (ZFS). Study of the ground-state electronic structures of integer-spin systems, like V 3+ , has received renewed attention in part due to the evolution of high field, high-frequency electron paramagnetic resonance (HFEPR) and inelastic neutron scattering spectroscopies [2][3][4][5].…”

“…A great deal of ground-state electronic structural information has been elucidated by studying these transitions using electronic absorption [7], luminescence [8], and Zeeman spectroscopies [6] for V 3+ in Al 2 O 3 , including the magnitude and sign of D and g-values. The analogous transitions of [V(ox) 3 ] 3À have received little attention [9]. This article describes the investigation of the electronic structure of [V(ox) 3 ] 3À diluted in NaMgAl(ox) 3 Á 9H 2 O by highresolution Fourier transform (FT) absorption and luminescence spectroscopies.…”

“…The analogous transitions of [V(ox) 3 ] 3À have received little attention [9]. This article describes the investigation of the electronic structure of [V(ox) 3 ] 3À diluted in NaMgAl(ox) 3 Á 9H 2 O by highresolution Fourier transform (FT) absorption and luminescence spectroscopies. FT spectroscopy combined with the narrow absorption line widths of the spin-forbidden d-d bands of V 3+ has allowed us to unambiguously resolve both axial and rhombic ZFSs within the 3 Â 2 component of the ground state [10].…”

“…The structure can be described as a 2D honeycomb lattice consisting of [NaAl(ox) 3 6 ] planes. The Al 3+ ions sit at a general position with C 1 symmetry.…”