Crystal and molecular structure of racemic 5,7,7,12,12,14-hexamethyl-1,4,8,11-tetra-azacyclotetradeca-4,14-dienenickel(II) perchlorate

Abstract

The structure of 5,7,7,12,12,14-hexamethyl-1,4,8,11-tetra-azacyclotetradeca-4,14-dienenickel(II) perchlorate has been determined and refined to R 0·062 for approximately 1000 reflections measured on a linear diffractometer. The complex crystallises in the orthorhombic space group Pbcn with a= 10·60, b= 11·11, c= 19·16 Å, Z= 4. A crystallographic two-fold axis passes through the cation which, as a consequence of the asymmetric nitrogen centres, is chiral; the space group ensures that the crystal is a racemate. The chiral isomer is more stable than the analogous meso-isomer because the C₂ symmetry allows greater freedom in the torsion angles for relief of strain energy than does the alternative C_s symmetry. Conformational analysis is used to point out the strong dependence of molecular geometry and, in particular, of metal–ligand-atom distances on geometrical constraints imposed by the cyclic ligand.