Planar nickel(II) complexes of different macrocyclic tetraazacyclotetradeca-4,11-diene ligands and diastereoisomers which differ in chiral carbon configurations have been separated by cation- exchange chromatography on SP-Sephadex C-25 resin. Of the limited number of successful eluents, sodium glycinate is the most effective. The separations are considered to result from differential associations between the glycinate anion and the complex cations. The technique has been successfully applied to the separation of the C-racemic and C-meso diastereoisomers of [Ni(ttcd)]²⁺ (ttcd = 5,7,12,14-tetramethyl-1,4,8,11- tetraazacyclotetradeca-4,11-diene). Diastereoisomers arising from chiral NH centres cannot be separated by this technique since the effective eluents are generally basic, causing epimerization. The use of ¹H and ¹³C n.m.r. spectra in these studies is discussed, and the isolation of the nickel(II) complex of the new macrocyclic ligand ptcd (5,7,7,12,14-pentamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene) by column chromatography described. The isolated [Ni(ptcd)]-(ClO₄)₂ is a mixture of the diastereoisomers C-axial,N-racemic and C-axial,N-meso.