Insights into the influence of dispersion correction in the theoretical treatment of guanidine-quinoline copper(I) complexes.

For the description of steric effects, dispersion correction is important in density functional theory. By investigation of sterically encumbered guanidine-quinoline copper bis(chelate) complexes, we could show that the correct description requires modern dispersion correction using Becke-Johnson (BJ) damping and that earlier dispersion corrections are not sufficient. The triple-zeta basis set def2-TZVP of the Ahlrichs series is balanced and converged for the structural description. With regard to functionals, the best structural description is obtained with the TPSSh functional but B3LYP is very suited as well. Cutting of ligand substituents leads to distortions which limit the predictive ability of such calculations. We recommend the calculation of "full" chemical systems with inclusion of dispersion correction using BJ damping. In the further analysis of the regarded copper bis(chelate) complexes, we found that the theoretical description of optical and Raman spectra is not much affected by the dispersion although charge transfer excitations come into play and that B3LYP/def2-TZVP is the best choice. Hence, we can derive the result that the correct structural description with dispersion serves as crucial basis for subsequent calculation steps.