class (a) metal ion 

https://doi.org/10.1351/goldbook.C01094
A metal ion that combines preferentially with @L03518@ containing ligating atoms that are the lightest of their Periodic Group.
See also: class (b) metal ion, hard acid
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1097 [Terms] [Paper]
Citation: 'class (a) metal ion' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.C01094 RIS BibTex EndNote
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Last revised: February 24, 2014