Metallacarboxylic acids exist in equilibria with the carboxylate anions, LMCO.
Metallacarboxylate esters (LMCOR) arise by the addition of alkoxide to metal carbonyl:
:[LM-CO] + ROH → [LM-COR] + H
Metallacarboxylic amides (LMC(O)NR) arise by the addition of amide to metal carbonyl:
:[LM-CO] + 2 RNH → [LM-C(O)N(H)R] + RNH
Derivatives of metalladithiacarboxylic acids are also known. They are prepared by treating anionic complexes with carbon disulfide.