Spin-density [V(D 2 O) 6 ] 2+ in ammonium-vandium Tutton salt : the metal-water bond

Abstract

Polarized neutron diffraction experiments on deuterated ammonium vanadium (II) Tutton salt and its solid solution with the zinc salt at 2.0 K and 4.6 T are reported. The unique reflection intensities were refined with a valence orbital model involving vanadium and water atom orbitals and a gaussian function to represent V–O overlap. The refinement gave X 2 = 0.81 and 0.74, respectively, with a vanadium unpaired electron configuration 3d–t 2.84(6) 2g ⋅3d–e -0.03(4) g . A substantial diffuse 4d–t 2g -like spin population occurs, together with a relatively large spin population on deuterium, which is evidence for π covalence in the plane of the water molecule, with spin donation from 3d–t 2g into diffuse metal and O–D bond regions. Negative spin, elsewhere in the σ framework, is evidence of appreciable spin polarization effects, and hence of electron-electron correlation. Comparison with the results from the nickel(II) and manganese(II) salts shows a consistent qualitative picture in accord with their varying 3d–t 2g and e g configurations. The covalence in all cases is small but appreciable. Spin polarization is marked both as the presence of negative spin regions and as the perturbations of populations from values expected from covalence effects. These results, particularly the dominance of π over σ bonding in the spin distribution confirm and extend earlier electron spin resonance (ESR), nuclear magnetic resonance (NMR) and theoretical studies on these and related systems.