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A study of the molecular structure and spectroscopic properties of polycyclic polyaza‐compounds with diamond‐lattice conformations
Author(s) -
Galasso V.,
Benedetti F.,
Jones D.,
Modelli A.
Publication year - 2001
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.1418
Subject(s) - chemistry , computational chemistry , crystallography , ab initio , density functional theory , valence (chemistry) , hexadecane , crystal structure , nuclear magnetic resonance spectroscopy , spectroscopy , lone pair , ab initio quantum chemistry methods , molecular orbital , stereochemistry , molecule , organic chemistry , physics , quantum mechanics
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 13 C 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