International audienceSingle crystal, X-ray structure determinations on several transition metal ion complexes of multidentate ligands involving hydroxyl-O, imine-N and heterocycle-N donor atoms have shown that both mononuclear and binuclear species can be formed, depending on the ligand, although the form obtained may depend simply upon the reaction stoichiometry. The structures have been analysed in terms of factors which may influence the complex ion nuclearity