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

摘要

Bis(N-alky1-2-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 Cu-II/Cu-I 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 degrees), these complexes are not planar in solution or as isolated molecules.