coordinatively unsaturated complex

https://doi.org/10.1351/goldbook.C01334
A transition metal complex that possesses fewer @L03518@ than exist in the @C01333@. These complexes usually have fewer than 18 outer shell electrons at the central metal atom.
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1100 [Terms] [Paper]