The molecular structure of three types of long-chain zinc(II) alkanoates for the study of oil paint degradation

The molecular structures of three types of zinc(II) alkanoates (Zn(Cn)2, ZnNa2(Cn)4 and ZnK2(Cn)4, Cn = CH3(CH2)n−2COO−, n = 8–18) were investigated by Fourier transform infrared spectroscopy (FTIR) and powder X-ray diffraction (PXRD) to aid the study of degradation phenomena in oil paint. Each type of complex forms a homologous series in the studied chain length range. For (Zn(Cn)2 and ZnNa2(Cn)4, these homologous series indicate that the long-chain complexes have structures highly similar to those published for short-chain single-crystal analogs. Moreover, we introduce a chain tilt factor FtiltFtilt to derive information about alkanoate chain angles from highly accurate PXRD long spacing values. The complex ZnK2(Cn)4 has not been reported before. It consists of metal sheets containing tetrahedrally coordinated Zn atoms and octahedrally coordinated K atoms bridged by effectively monodentate carboxylate groups, and alkanoate chains that are tilted relative to the long axis.

Graphical abstractThe molecular structures of long-chain zinc(II) alkanoates were studied by FTIR and XRD as references for oil paintings research. It was found that zinc mixed metal complexes form with sodium and potassium. The carboxylate coordination geometries and chain tilts in long-chain structures are very similar to those in short-chain complexes.Figure optionsDownload full-size imageDownload as PowerPoint slide