Hydrogen-bond geometry and its isotope effect in crystals with OHO bonds - revisited

The O-H vs O ... O correlation in OHO hydrogen bonds is briefly reviewed based on the development during these twenty years and the geometric isotope effect Delta R is revised including the new data. It is pointed out that the following still remains to be settled: (1) whether or not the O-H distances in asymmetric bonds for the same O ... O distance scatter in shea hydrogen bonds at low temperature; (2) whether there exists or not the exceptional compounds that exhibit the extraordinarily large geometric isotope effect (similar to 0.1 Angstrom); (3) where the critical hydrogen-bond distance is located; and (4) the peculiar hydrogen-bond geometry and its origin in high-pressure ice. (C) 2000 Elsevier Science B.V. All rights reserved.