A study of the molecular structure and spectroscopic properties of polycyclic polyaza-compounds with diamond-lattice conformations

Abstract

The equilibrium structures of a selection of polycyclic polyaza-compounds, characterized by diamond-lattice arrangements and conformational flexibility, were investigated with the density functional method B3LYP/6-31G(d,p). The 10- or 12-membered central ring in two tricyclic tetraaza-compounds, formally derived from tricyclo-hexadecane and tricyclo-octadecane, respectively, prefers a “square” geometry. The 16- or 24-membered central ring in nonacyclic octaaza-compounds, related to pentacyclo-octacosane, and in nonacyclic dodecaaza- and hexadecaaza-compounds, both related to nonacyclo-tetratetracontane, can instead adopt two or three alternative conformations with “square” or “rectangular” geometry. The theoretical structural models are consistent with evidence from NMR and X-ray spectroscopy. In addition, they provide a satisfactory account of the 13C NMR chemical shifts, which were predicted with a continuous set of gauge transformation calculations performed with the B3LYP/6-311+G(2d,p) formalism. The electronic structure was also studied by means of ab initio outer valence Green function calculations, which give a consistent, overall description of the different manifolds of photoionizations, associated with the nitrogen lone pair orbitals. Electron transmission spectroscopy was employed to detect the low-lying temporary anion states of some representative compounds. © 2001 John Wiley & Sons, Inc. Int J Quant Chem, 2001