On the structure and spectroscopic properties of the cis- and trans-isomers of cyclen- and cyclam-glyoxal

Abstract

The equilibrium structures of the cis- and trans-isomeric derivatives of the cyclen and cyclam condensation products with glyoxal were investigated with the density functional theory (DFT) model B3LYP/6-31G(d,p). According to calculations, the trans-fused condensation product is more stable than the cis product by 2kcalmol−1 in the case of cyclam. For cyclen, the stability order is instead inverted, the cis-fusion being much more preferred by 9.8kcalmol−1. The 13C NMR chemical shifts were recorded and analyzed by means of continuous set of gauge transformations (CSGT) calculations performed with the HF-B3LYP/6-311+G(2d,p) hybrid functional model. The He(I) photoelectron spectra were measured and interpreted by means of ab initio outer valence Green function (OVGF) calculations, which give a consistent, overall description of the uppermost bands, associated with the four nitrogen lone pair orbitals.