Solid-state multinuclear magnetic resonance investigation of Pyrex®

Pyrex® is an ubiquitous material that has attained widespread use in laboratory glassware and household utensils due to its properties, cost effectiveness, and ease of fabrication. Despite its importance, the structure of borosilicate glass such as Pyrex® is not fully understood. Here, we report high resolution 29Si, 27Al, and 11B magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopic measurements at 9.4 and 19.5 T, combined with 27Al and 11B multiple-quantum MAS (MQ-MAS), and 11B Rotor Assisted Population Transfer (RAPT), to identify structural features in Pyrex®. A distribution of Q4 silicon and aluminum sites is observed, and there is no evidence of five or six coordinated aluminum. The 27Al quadrupolar coupling constants for the tetrahedral aluminum varied from 3.5 to 4.5 MHz, while the isotropic chemical shifts varied from 50 to 65 ppm. Boron-11 measurements resolve four distinct distributions in boron environments: two identified as tetrahedral, BO4, and two as trigonal, BO3. Tetrahedral sites are distinguished by different second coordination spheres, e.g., BO4(0 B, 4 Si) and BO4(1 B, 3 Si), and the trigonal sites based on the symmetry of the boron environments.