ORIENTATION OF THE QUADRUPOLE AND DIPOLE TENSORS OF HYDROXYL-GROUPS BY O-17 QUADRUPOLE SEPARATED LOCAL-FIELD NMR

The static O-17 NMR spectra of Mg(OH)(2) and amorphous ME(OH)(x)(OCH3) (2-x) were measured. Simulation of these spectra gave e(2)qQ/h=6.8MHz, eta=0, and delta(iso)=20 ppm, and e(2)qQ/h =7.25 MHz, eta=0, and delt a(iso)=-25 ppm for the hydroxyl oxygen in, respectively, Mg(OH)(2) and Mg(OH)(x)(OCH3)(2-x). An OH distance in Mg(OH)(2) of 1.001 Angstrom w as obtained using Lee-Goldberg decoupling to obtain the OH dipolar cou pling constant. Dipolar oscillations in the H-1-O-17 cross-polarizatio n curve provided an OH distance of 0.995 Angstrom in Mg(OH)(x)(OCH3)(2 -x); these oscillations were not observed in Mg(OH)(2). Based on diffe rences in the OH distance and in the O-17 quadrupole coupling constant it was concluded that the OH bond in Mg(OH)(x)(OCH3)(2-x) was more co valent. O-17 2D quadrupole separated local field experiments were perf ormed on both samples in order to obtain the relative orientation of t he O-17 quadrupole and OH dipole tensors. In both cases the interactio n tensors were found to be collinear. Lee-Goldberg decoupling during t he dipolar evolution time t(1) improved the resolution in the dipolar dimension. The resolution in the dipolar dimension of the 2D spectra o btained without proton decoupling during t(1) was better for the Mg(OH )(x)(OCH3)(2-x) sample than for the Mg(OH)(2) sample. Since the effect of the homonuclear proton dipolar coupling was less prominent in the amorphous sample, as evidenced by difference in CP-dynamics and spectr al resolution, it was concluded that the hydroxyl groups were more iso lated in the amorphous sample. The simulation of 2D separated quadrupo le local field spectra showed that the experiment is very sensitive to differences in the relative quadrupole and dipole tensor orientation. (C) 1998 American Institute of Physics.