Two complexes of [Cu(L)H2O](ClO4)2, 1 and [Cu(L)H2O](NO3)2, 2 containing hemilabile tetradentate ligand of 3,3'-(piperazine-1,4-diyl)dipropanamide, L, were synthesized and characterized by elemental analyses, spectroscopic (IR, UV–Vis, X-ray) data, molar conductance measurements and X-ray crystallography. The solvatochromic behavior of complex 1 was examined in the selected solvents (nitromethane, acetonitrile, propionitrile, acetone, tetrahydrofuran, ethanol, methanol, dimethylformamide, dimethylsulfoxide, and hexamethylphosphorictriamide), observing positive solvatochromism. The observed solvatochromism was analyzed by a statistical method. The obtained results confirm that the donor number (DN) parameter has the dominant contribution in the observed solvatochromism. For cationic complex 2 density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations was carried out to explore the mechanism of the solvatochromic behavior of the complex and satisfactory theoretical–experimental agreement was achieved. Additional information about the relative stability of Cu-N(amide) over Cu-O(amide) isomers was obtained by DFT analysis. The complexes were also observed to exhibit thermochromism in the solvent of dimethyl sulfoxide.
