Infrared, Raman and computational study of a crystalline mononuclear copper complex of relevance to the pigment Verdigris

Vibrational spectroscopy is widely used in the study of pigments and degradation processes in historical art objects. Bis(acetato-κ2O,O) diammine copper(II) [Cu(MeCOO)2(NH3)2] shares coordination features with some types of copper soaps found in paint layers containing the green pigment Verdigris. In this study, we present new insights based on observed vibrational (IR, Raman) spectra. The Raman spectrum is presented for the first time, while only very early IR data were previously available. The interpretations are supported by quantum chemical calculations. The model calculations for a dimeric cluster model show the importance of including at least two metal complex units and an extended hydrogen-bond network to properly simulate the crystal environment. Decent agreement with experimental spectra was achieved applying a DFT-level layered integrated molecular orbital model.