AbstractBy infrared spectroscopy it is shown that trialkyltin acylates in the solid state occur as coordination polymers in which each tin atom is penta‐coordinated,viz. by three alkyl groups and two oxygen atoms belonging to different acylate groups. In apolar solvents or in the liquid state, however, the compounds are monomolecular and show resemblance to organic esters. Only in very concentrated solution or just above the melting point is association detected. In a search for the generality of the concept it was found that the occurrence of the polymeric crystal structure is counteracted by steric hindrance, that it does not occur with thio‐ or dithio‐acetates and, finally, that lead behaves like tin but germanium and silicon compounds are monomolecular throughout.