Studies on Mixed Chelates. XII. Formation and Electronic Spectra of 5-Coordinated Mixed Copper(II) Chelates Containing N-Alkylated Ethylenediamine, Acetylacetonate, and Pseudohalide Anions

The visible absorption spectra of three new mixed chelates of copper (II), Cu(tmen)(acac)X(tmen=N,N,N′,N′-tetramethylethylenediamine, acac=acetylacetonate ion, X=NCS, N3, or NCO) were studied in various organic solvents. It was found that the \ ildeνmax values of their d-d bands depend strongly on the nature of the solvent, and shift in the opposite direction as compared with the case of [Cu(tmen)(acac)]ClO4 studied before, where \ ildeνmax shifted to red with the increase of the donor number (DN) of the solvent. Here the magnitude of the red shift is affected not only by the DN, but also by other parameters of the solvent polarity, such as Kosower’s Z or Reichardt’s ET. The obtained data can reasonably be explained, if an equilibrium [Cu(tmen) (acac)X][Cu(tmen)(acac)]++X− (5−coordinated)(4−coordinated) (with axial solvation) is assumed to exist in such solutions.