Characterization of Mo(CO)(6) by Mo-95 single-crystal NMR spectroscopy

Single-crystal Mo-95 NMR spectra for a crystal of Mo(CO)(6) have been acqui red for the central and satellite transitions at a high magnetic field (14. 1 T). The spectra are analyzed in terms of the quadrupole coupling and chem ical shielding tensors. Parameters of high precision for the magnitudes, re lative, and absolute orientations of these tensors are determined. The orie ntations of the two tensors are obtained without any a priori knowledge on the crystal symmetry of the Mo(CO)(6) octahedron. The optimized Euler angle s, describing the relative orientation of the two tensors, are in accordanc e with the location of the Mo atom in a crystallographic mirror plane as al so seen from the crystal structure of Mo(CO)(6) (orthorhombic, Pnma). The d ata from single-crystal NMR fully confirm the magnitudes and relative orien tation of the quadrupole coupling and chemical shielding tensors determined in a recent Mo-95 static-powder NMR study of Mo(CO)(6). Thus, uncertaintie s about the reliablility of particularly the three Euler angles, describing the relative orientation of the tensor for the very small chemical shieldi ng anisotropy and the quadrupole coupling tensor, have been clarified. Fina lly, it is shown that slow-speed spinning Mo-95 MAS NMR at a high magnetic field (14.1 T) allows determination of the NMR parameters with good precisi on for the two tensorial interactions, despite the small chemical shielding anisotropy.