Experimental and computational characterization of structural and spectroscopic features of mixed ligand copper complexes-prototypes for square-pyramidal stereochemistry

Two new mixed ligand copper complexes with 1,10-phenanthroline and monodentate pyrazoles (3,5-dimethyl-4-R-pyrazole, where R = nitro or iodo), stand as case-studies for a revisited view on Ligand-Field (LF) qualitative and semi-quantitative issues, brought in conjunction with the rich information offered by the state-of-the art computational methods. The combined analysis of the first TD-DFT energies and density difference maps enables a scheme of the LF split in the complexes with a specific variety of square-pyramidal coordination geometry, namely the case when the pi-type anisotropy due to the two types of aromatic amine ligands shows different orientation with respect of the averaged basal plane. The density difference maps were used as ancillary tools for checking the coordination process and observing the nephelauxetic effect. Clear correlations are drawn between computed and experimental UV-Vis and EPR spectra, rationalizing the Lande factors in terms of Ligand Field states. (C) 2019 Elsevier Ltd. All rights reserved.