The room temperature structures of anhydrous zinc(II) hexanoate and pentadecanoate

The room temperature structures of anhydrous zinc (II) hexanoate and pentadecanoate have been studied using infrared spectroscopy, X-ray diffraction and polarizing light microscopy. Lattice parameters from single crystal X-ray and powder diffraction data, for short chain length hexanoate, are compared to validate the powder method which is then used, in conjunction with density and other molecular calculations to determine the structure of the longer chain length pentadecanoate. The compounds are isostructural; in that, each zinc atom is tetrahedrally coordinated to oxygen atoms of four different carboxylate groups and each ligand forms a bidentate bridge with two tetrahedral zinc atoms in a syn–anti arrangement. Bonding is unsymmetrical around the zinc atom. For both compounds, hydrocarbon chains, in the fully extended all-trans configuration, are tilted at an average angle between 58 and 61° to the planes containing zinc ions, though, in the case of the hexanoate, a bilayer arrangement of hydrocarbon chains within a lamella is indicated. The arrangement of the chains within the bilayer is regular with a similar side chain interaction for all the hydrocarbon moieties. For the longer chain length compound, an interdigitated bilayer arrangement of chains within a lamella is proposed. For this, an alternating head-to-tail arrangement within the layers between zinc atoms is indicated from the X-ray data. Nevertheless, both compounds crystallize within a monoclinic unit cell with P1c1 symmetry, at least for the hexanoate, with the chains arranged in a two dimensional network along the ac plane within the unit cell.