Some electron paramagnetic resonance studies of bis-cyclopentadienyl vanadium

Abstract

Section I: Bis-cyclopentadienyl vanadium was examined by electron paramagnetic resonance (EPR) in dilute benzene solution (1). Vanadium nuclear hyperfine splittings equal to 77 Mc centered at g=2.00 were found, providing experimental evidence that the unpaired electrons occupy orbitals with a very small amount of s character. The orbital ground state is shown to be a singlet. It follows that one of the three unpaired electrons must occupy an orbital of a_(1g) symmetry, the other two orbitals of e_g symmetry, and that the g factor is nearly isotropic. EPR spectra taken of an oxidized solution show hyperfine structure 210 Mc wide at g=1.99, indicating the possible presence of bis-cyclopentadienyl vanadyl, V0(C_5H_5)_2. Section II: EPR spectra were taken of a dilute single crystal of bis-cyclopentadienyl vanadium in ferrocene and the angular dependence of the spectra studied. The spectral lines changed from g^e≃2 at a position with H_0 approximately parallel to the molecular symmetry axis to g^e=3.77 with H_0 perpendicular to this axis, where hν=g^eβH. This angular dependence indicates a zero-field energy level splitting of 47.0 kMc or 1.57 cm^(-1). The bis-cyclopentadienyl vanadium was synthesized by a process originated by Wilkinson (2) but some minor changes were found desirable in product recovery.