The differences in complexation behaviour of two diastereomeric tetraazamacrocycles, meso (1) and racemic (2) 5,5,7,12,12,14-hexamethyl-l,4,8,1l-tetraazacyclotetradecane, are explained by different conformations in solution, 1 being one stable conformer of almost rigid structure while 2 shows higher conformational flexibility to avoid steric strain. The methods used were 'H and I3C NMR and molecular modelling.