SI-29 NUCLEAR MAGNETIC-RESONANCE SPECTRA OF TRANSITION-METAL SILICIDES

The 29Si chemical shielding parameters derived from 29Si nuclear magnetic resonance (NMR) spectra of 25 silicides of Group IVB, VB, VIB, VIIB, and VIII metals are presented. The isotropic shifts of these silicides span the range from -1650 to + 925 ppm relative to TMS and have shielding anisotropies -250 to + 335 ppm; these extremes are approximately ten times as large as those of organosilicon and silicon oxide compounds. For silicides of Ti, Zr, Nb,Ta,Cr,Mo,W,Rh, Ni,Pd, Pt, and Cu, the chemical shielding interaction is sufficiently larger than the extraneous spectral broadening to allow detection of multiple phases owing to different crystal structures and local differences in stoichiometry. The potential to detect multiple phases in silicides of Hf, V, Mn, Fe, Ru, and Co is less owing to smaller differences in isotropic shifts and/or broadening that overwhelms the chemical shielding information. However, it is possible that the broadening is not an inherent property of these silicides, but rather suggests the presence of structural defects in these particular samples.