Abstract
Irradiation of ammonium paramolybdate yields a paramagnetic centre which is trapped uniquely on one of the molybdenum atoms in the {Mo7O24}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.