Structure and reactivity of the oxyanions of transition metals. Part XVII. A study of NbO4 2? in calcium molybdate by electron spin resonance
- 1 January 1968
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in J. Chem. Soc. A
- p. 2985-2990
- https://doi.org/10.1039/j19680002985
Abstract
A paramagnetic centre, thought to be NbO4 2–, has been obtained by γ-irradiation of a single crystal of CaMoO4 : Sm: Nb at 77°K. At 77°K it appears in four magnetically distinct sites and the e.s.r. spectra can be described by an anisotropic spin Hamiltonian with principal values of the g- and A-tensors given by gxx= 2·0061, gyy= 2·0146, gzz= 2·0480, and Axx=–25·5, Ayy=–28·5, Azz=–30·5 gauss. The two tensors are approximately spatially coincident with gzz lying close to one of the Nb–O bonds. Also, isotropic super-hyperfine interaction with one neighbouring MoO4 2– anion was observed with A′iso= 2·2 G. At 195°K there is only one distinct site and the spin Hamiltonian is axially symmetric having g∥= 2·0208, g⊥= 2·0250 and A∥=–27·9, A⊥=–27·0 G, the unique direction lying along the crystallographic c axis. The magnetic parameters at 77°K are best reproduced in terms of a model in which the electron deficiency of NbO4 2– is localised almost entirely in an oxygen π-orbital. The super-hyperfine coupling to Mo is interpreted in terms of weak bonding between NbO4 2– and one of the four nearest-neighbour MoO4 2– ions, and the results at 195°K are then explained in terms of a rapid jumping between the four equivalent sites.Keywords
This publication has 0 references indexed in Scilit: