Stereochemical Properties of Multidentate Nitrogen Donor Ligands and Their Copper Complexes by Electronic CD and DFT

Abstract

UV-Vis and electronic circular dichroism (ECD) spectroscopy, complemented with Density Functional Theory (DFT) calculations, were used to elucidate the structural diversities of three multidentate nitrogen donor ligands and two associated copper complexes in solution directly. The three chiral salen ligands all consist of trans-cyclohexane-1,2-diamine as a chiral scaffold and also of pyridine rings as chromophores, differing only in the linking groups between the two functional groups mentioned above. Very different ECD intensities and somewhat different ECD patterns were observed for these ligands and satisfactorily interpreted theoretically. For the geometry optimization and spectral simulation of the open-shell metal complexes, the LANL2DZ basis set with effective core potential for the Cu and Cl atoms and pure cc-pVTZ for the rest of the atoms was utilized. The performance of the same calculations with the polarization functions (f,g) from the cc-pVTZ basis added to the LANL2DZ basis was compared. While the three ligands exhibit different conformational flexibility, the associated copper complexes show great rigidity imposed by the metal-ligand coordination, taking on a single structure in each case. In addition, dispersion interactions were shown to change the conformational stability ordering of the ligands noticeably and to exert considerable influence on the simulated UV-Vis and ECD spectra. Chirality 28:545-555, 2016. © 2016 Wiley Periodicals, Inc.

Diagnostic Absolute Configuration Determination of Tetraphenylethene Core-Based Chiral Aggregation-Induced Emission Compounds: Particular Fingerprint Bands in Comprehensive Chiroptical Spectroscopy

“…Comparing to the above-mentioned time-consuming and pricy methods, comprehensive circular dichroism spectroscopy combined with the theoretical simulation is a promising and convenient tool for AC determination in terms of its simple procedure, high-efficiency, and spectral stability. − ECD represents a versatile and efficient tool to analyze chiral sample with suitable chromophores and has been considered as a common tool “to look at the stereochemistry of the molecule through the eyes of the chromophore”. , VCD, on the other hand, as the extension of ECD into the infrared region, is characterized by differential absorption of left- and right-handed polarized IR light . Including many well-resolved IR bands, VCD spectroscopy has become an increasingly important method for AC assignment. − In contrast to XRD technique, VCD and ECD do not require the presence of heavy atoms in the molecule and they avoid complicated sample pretreatment prior to analysis.…”