ELECTRON-PARAMAGNETIC RESONANCE OF MO-95-DOPED AND MO-97-DOPED CRYSTALS OF TETRAPHENYLARSONIUM OXOPENTAISOTHIOCYANATONIOBATE(V) - DETERMINATION OF THE MO-97 NUCLEAR-QUADRUPOLE TENSOR

Successful preparation and electron paramagnetic resonance of 95Mo- and 97Mo-doped single crystals of tetraphenylarsonium oxopentaisothiocyanatoniobate(V) are described. The following nuclear quadrupole coupling constants were determined for 97Mo: QD = 3.0± 0.2 MHz and QE = 0.1 ± 0.05 MHz. The principal axes of A(Mo) are coincident within error with those of P(Mo), but not with those of g. The principal values of g and the noncoincidence between the principal axes of g and A(Mo) vary for the MoO(SCN)52- anion when doped into different host materials and dissolved in solution. Random misalignment of the guest impurity in the host material accounts for the differences in linewidths of the six primary molybdenum hyperfine transitions in single-crystal spectra, while 14N nuclear quadrupole interaction accounts for the anisotropic line broadening. Anomalous orientation-dependent frozen-solution" spectra of TPA2NbO(SCN)5 in CHCl3 are explained in terms of alignment of suspended crystallites in solution by the external magnetic field. © 1979."