Metal complexes of the type
RCMLn (M = metal, L = ligand) in which formally a carbyne is coordinated to a metal, e.g.
M03861.png
Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1349 (https://doi.org/10.1351/pac199567081307)