Substituent Effects on Structural, Electronic, and Redox Properties of Bis(N‐alkyl‐2‐oxy‐1‐naphthaldiminato)copper(II) Complexes Revisited – Inequivalence in Solid‐ and Solution‐State Structures by Electronic Spectroscopy and X‐ray Diffraction Explained by DFT

Abstract

AbstractBis(N‐alkyl‐2‐oxy‐1‐naphthaldiminato)copper(II) complexes in the solid state and in N,N′‐dimethylformamide (DMF) solutions were studied by electronic spectroscopy, X‐ray diffraction, DFT calculations, and cyclic voltammetry. The established correlation between the bulkiness of the imine nitrogen substituent, deformation of the copper coordination sphere, and the CuII/CuI couple potential in DMF solutions has been re‐evaluated, and its inconsistencies explained by using results from DFT calculations and spectroscopic data. According to these DFT calculations, the coordination sphere of the N‐ethyl derivative has a flat‐tetrahedral geometry. The N–Cu–N′ and O–Cu–O′ angles and the dihedral angle between the planes N–Cu–O and N′–Cu–O′ in the solid state found by X‐ray diffraction in this study are affected by crystal packing forces. UV/Vis spectra of the N‐ethyl, N‐iPr, and N‐tBu derivatives suggest that the first two compounds have fluxional behavior characterized by a centrosymmetric transition state, whereas the tBu group in the N‐tBu derivative prevents such dynamic action. In the crystal, this N‐tBu complex changes upon DFT geometry optimization to a more tetrahedral configuration. Therefore, in contrast to X‐ray crystal structures reported in the literature of complexes with primary N‐alkyl substituents that show a planar Cu coordination sphere (i.e. N–Cu–N′ and O–Cu–O′ bond angles of 180°), these complexes are not planar in solution or as isolated molecules.