Many different ring conformations are possible for cyclen: tetraazacyclododecane. Conformation energies were calculated using molecular mechanical method for cyclo-dodecane. Ten different ring conformations were realized for 1, 4, 7, 10-tetrabenzyl-2, 5, 8, 11-tetraethyl-1, 4, 7, 10-tetraazacyclododecanes and their metal complexes.