Crystal and molecular structure of 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane: Energy and structural relationships for this tetraazamacrocycle in its neutral and protonated forms

The X-ray crystal structure of 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane has been determined. The neutral ligand crystallises in the triclinic space groupP with unit cell parametersa=8.467(4),b=10.057(5),c=10.637(5) Å, =67.68(3), =75.38(4), =76.34(4)°,V=800.75 ų andD _c=1.063 g cm^–3 forZ=2.R=0.047 for 2140 unique observed (I/(I)2.0) reflections (R _w=0.052). Two crystallographically independent molecules are observed. Both are centrosymmetric and adopt a mesodentate conformation. Molecule (1) is identified as the (R, S, S, R)-trans-IV] isomer and molecule (2) as the (R, R, S, S)-trans-III] isomer. Molecular mechanics calculations provide a basis for understanding the structural and energetic relationships between the neutral and protonated forms of this tetraazamacrocyclic ligand. Supplementary Data relating to this article have been deposited with the British Library at Boston Spa, Wetherby, West Yorkshire, U.K. as Supplementary Publication No. 82149 (13 pages).