hard base

Also contains definition of: soft base
https://doi.org/10.1351/goldbook.H02742
A @L03511@ with a donor centre (e.g. an oxygen atom) of low @P04711@ the converse applies to soft bases.
See also:
hard acid
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1120 [Terms] [Paper]