Single crystal proton ENDOR of γ-irradiated ammonium paramolybdate at 15 K

Abstract

Irradiation of ammonium paramolybdate yields a paramagnetic centre which is trapped uniquely on one of the molybdenum atoms in the {Mo7024} 6-ion. The centre has low symmetry so that its location cannot be deduced from the E.S.R. parameters. Hyperfine coupling tensors for six protons have been obtained from ENDOR measurements at 15 K and interpreted in the point-dipole approximation to construct the proton geometry in the vicinity of the paramagnetic centre. Comparison of this model with the heavy atom positions, known from X-ray diffraction, has enabled the location of the paramagnetic centre to be identified.

Photo- and Electrochromism of Polyoxometalates and Related Materials

“…ENDOR results for the γ-irradiated single crystal of [NH 4 ] 6 [Mo 7 O 24 ]·4H 2 O indicate that a MoO 5 (OH) center is formed at one of the four MoO 6 octahedra having C 4 symmetry within the C 2 v symmetry anion. This center is formed as a result of direct decomposition of an NH 4 + ion . The proton is estimated to be 1.46 Å from the terminal O atom, which is close to the limits of applicability of the point−dipole approximation.…”

“…This center is formed as a result of direct decomposition of an NH 4 + ion. 92 The proton is estimated to be 1. 46 4).…”