Syntheses of mixed chelate copper(II) complexes containing β-ketoaminato and diamine ligands: Solvatochromism study

Three new mixed-chelate Cu(II) complexes incorporating N,N,N′,N′-tetramethylenediamine (tmen) or N,N-dimethyl,N′-benzyl-ethylenediamine (dmben) as diamine chelate and a β-ketoaminato such as 4-amino-3-penten-2-onato (APO) or 3-amino-3-phenyl-2-buten-1-onato (APBO) with the general formula [Cu(β-ketoamine)(diamine)]ClO4 were prepared and characterized. Their solvatochromic properties were studied by visible spectroscopy. X-ray crystal analysis confirmed that copper (II) ion in [Cu(APO)(tmen)]ClO4 and[Cu(APBO)(tmen)]ClO4 is almost in a square planar environment. Structure of [Cu(APO)(dmben)]ClO4 was investigated by DFT calculation. The solvent-dependent visible spectroscopic absorption maxima, νmax, were analyzed using stepwise multiple linear regression (SMLR) method to find the best model explaining the observed positive solvatochromism. The analysis demonstrated that among different solvent parameters, donor number (DN) is a dominant factor responsible for the shift in the d–d absorption band of the complexes to the lower wavenumber with increasing its values. The importance of steric effect in the diamine ligand and more delocalization of pi-bands in the β-ketoamine on the spectral and SMLR measurements are discussed.