Electron spin resonance studies in an irradiated single crystal of hexakis(ammonium) diformylated octamolybdate dihydrate

Abstract

X-Band e.s.r studies on Mo^v centres formed by an u.v.-irradiated single crystal of the title compound, (NH₄)₆[(CHO)₂Mo₈O₂₈]·2H₂O, have been carried our at room temperature.Analyses of the e.s.r. spectra show that there are two different paramagnetic species in the unit cell. One may be resolved superhyperfine lines due to the interaction of the Mo^v centre with a ¹H atom; the other can only be resolved hyperfine lines due to the Mo^v centre.The spin-Hamiltonian parameters have been rigorously calculated using a least-squares-fitting technique, specially adapted to non-coincident g- and A-tensor systems. The principal values of the g, A_Mo and A_H tensors for the two species, as well as the direction cosines of their principal axes with respect to the reference system, are obtained. The spin density and bond nature of the Mo^V—O bond are estimated according to the principal values of the A tensors. The results indicate the main component of the ground -state molecular orbital is the atomic orbital 4d_xy of the Mo^V paramagnetic centre. The Mo^V—O bond is an ionic bond with a covalent component.