Glassy metal-organic frameworks: The node-and-linker structure of metal-organic frameworks could enable detailed structural studies of molecular glasses quenched from melts. Zinc-based zeolitic imidazole frameworks exhibit a high propensity for glass formation at conventional cooling rates. Madsen et al. used ultrahigh magnetic fields (19.5 and 35.2 tesla) to perform zinc-67 nuclear magnetic resonance of solid samples with magic-angle spinning on three samples with different ratios of imidazole and benzimidazole linkers. The structural disorder of the tetrahedral ligand environment around zinc nodes was higher in the glassy states than in the parent crystals. Science , this issue p. 1473

Pressure induced correlated evolution of the distributions of the Si–O distance and Si–O–Si inter-tetrahedral bond angle in vitreous silica quenched from pressures of up to ∼14 GPa at ambient temperature is measured in unprecedented detail using two-dimensional dynamic-angle-spinning ¹⁷O nuclear magnetic resonance spectroscopy. The results demonstrate that, in contrast to the conventional wisdom, vitreous silica undergoes irreversible structural changes even at pressures as low as ∼8 GPa. These structural changes at the short range involve a progressive reduction in the mean Si–O–Si angle and a broadening of the corresponding distribution, with increasing pressure. This bond angle reduction is accompanied by a concomitant monotonic increase in the mean Si–O distance. The mean values of the Si–O–Si angle and Si–O distance at various pressures closely follow the minimum in the corresponding potential energy surface calculated for the H₆Si₂O₇ dimer molecule.