Theoretical interpretation of ~(17)O NMR chemical shift in borosilicate glass by molecular orbital calculations

摘要

In borosilicate glasses, ~(17)O 3QMAS NMR spectra arc successfully separated into the components assigned to the oxygen sites. SiOSi, SiOB, and BOB. However, the assignments have been done empirically, and theoretical interpretations have never been given in borosilicate glasses. Hence, we performed molecular orbital calculations by using the Gaussian03 program to interpret ~(17)O NMR peaks. Various cluster models containing SiOSi, SiOB[3], SiOB[4], B[3]OB[3], B[3]OB[4] and B[4]OB[4] units (B[n]: n-fold coordinated boron) were constructed by a geometrical optimization using B3LYP/6-31+G(d). ~(17)O NMR chemical shift (delta_i~o) was calculated using HF/6-311+G(2df,p) and GIAO method for the magnetic shielding tensor calculation.