Journal of Physical Chemistry A, Vol.101, No.30, 5463-5468, 1997
Solid-State Mo-95 NMR-Studies of Some Prototypal Molybdenum Compounds - Sodium Molybdate Dihydrate, Hexacarbonylmolybdenum, and Pentacarbonyl Phosphine Molybdenum(0) Complexes
Molybdenum-95 nuclear quadrupolar coupling constants, chi(Mo-95), and quadrupolar asymmetry parameters, eta, for sodium molybdate dihydrate, hexacarbonylmolybdenum(0), pentacarbonyl-5-methyldibenzophospholemolybdenum(0), and pentacarbonylbis(diphenylphosphino)methanemolybdenum(0) were obtained from solid-state Mo-95 NMR measurements at 26 MHz (9.4 T). The first direct measurements of (1)J(Mo-95, C-13) and (1)J(Mo-95, P-31) from solid-state Mo-95 NMR spectra are reported. Also, the first example of a C-13/C-12 isotope effect on Mo-95 shielding is reported for solid Mo(CO)(6) : (1) Delta Mo(C-13/12) = -0.316 ppm. Direct-dipolar spin-spin interactions involving protons and molybdenum (i.e., H-1-Mo-95) are relatively weak and do not appear to make significant contributions to Mo-95 NMR line shapes when spectra are acquired with magic-angle spinning. Hexacarbonylmolybdenum is proposed as a useful setup sample for solid-state Mo-95 NMR studies. Our results for the pentacarbonyl phosphine molybdenum complexes indicate that solid-state Mo-95 NMR studies should be feasible for a range of molybdenum(0) octahedral complexes. These studies will be facilitated by using applied magnetic fields well above 10 T.
Keywords:NUCLEAR MAGNETIC-RESONANCE;O-17 RELAXATION-TIMES;QUADRUPOLE COUPLING-CONSTANTS;METAL-CARBONYLS;CHROMIUM HEXACARBONYL;ELECTRONIC-STRUCTURE;NEUTRON-DIFFRACTION;CRYSTAL-STRUCTURE;CHEMICAL-SHIFTS;SPECTROSCOPY