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(C-n)(2), ZnNa2(C-n)(4) and ZaK(2)(C-n)(4), C-n = CH3(CH2)(n-2)COO-, 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(C-n)(2) and ZnNa2(C-n)(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 F-tilt to derive information about alkanoate chain angles from highly accurate PXRD long spacing values. The complex ZnK2(C-n)(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.