title: Solid state ¹³C-NMR, infrared, X-ray powder diffraction and differential thermal studies of the homologous series of some mono-valent metal (Li, Na, K, Ag) n-alkanoates: a comparative study.
abstract: A comparative study of the molecular packing, lattice structures and phase behaviors of the homologous series of some mono-valent metal carboxylates (Li, Na, K and Ag) is carried out via solid state FT-infrared and (13)C-NMR spectroscopes, X-rays powder diffraction, density measurements, differential scanning calorimetry, polarizing light microscopy and variable temperature infrared spectroscopy. It is proposed that, for lithium, sodium and potassium carboxylates, metal-carboxyl coordination is via asymmetric chelating bidentate bonding with extensive intermolecular interactions to form tetrahedral metal centers, irrespective of chain length. However, for silver n-alkanoates, carboxyl moieties are bound to silver ions via syn-syn type bridging bidentate coordination to form dimeric units held together by extensive head group inter-molecular interactions. Furthermore, the fully extended hydrocarbon chains which are crystallized in the all-trans conformation are tilted at ca. 30°, 27°, 15° and 31° with respect to a normal to the metal plane, for lithium, sodium, silver and potassium carboxylates, respectively. All compounds are packed as lamellar bilayer structures, however, lithium compounds are crystallized in a triclinic crystal system whilst silver, sodium and potassium n-alkanoates are all monoclinic with possible P1 bravais lattice. Odd-even alternation observed in various physical features is associated with different inter-planar spacing between closely packed layers in the bilayer which are not in the same plane; a phenomenon controlled by lattice packing symmetry requirements. All compounds, except silver carboxylates, show partially reversibly first order pre-melting transitions; the number of which increases with increasing chain length. These transitions are associated, for the most part, with lamellar collapse followed by increased gauche-trans isomerism in the methylene group assembly, irrespective of chain length. It is proposed that the absence of mesomorphic transitions in their phase sequences is due to a lack of sufficient balance between attractive and repulsive electrostatic and van der Waals forces during phase change. The evidence presented in this study shows that phase behaviors of mono-valent metal carboxylates are controlled, mainly, by head group bonding.
authors: Department of Materials and Interfaces, Weizamann Institute of Science, Rehovot, Israel. Electronic address: chessnelo@yahoo.co.uk.
authors: Peter N
authors: PN
authors: Nelson
authors: Department of Chemistry, University of the West Indies, Mona, Kingston 7, St. Andrew, Jamaica.
authors: Henry A
authors: HA
authors: Ellis
authors: Department of Science, Northern Caribbean University, Mandeville, Manchester, Jamaica.
authors: Nicole A S
authors: NAS
authors: White
mesh_terms: D000473:Alkanes / Q000737:chemistry*; D066241:Carbon-13 Magnetic Resonance Spectroscopy; D004055:Differential Thermal Analysis; D008670:Metals / Q000737:chemistry*; D011208:Powders; D013055:Spectrophotometry, Infrared; D055672:Static Electricity; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: D000473:Alkanes; D008670:Metals; D011208:Powders
keywords: All-trans; Lamellar; Mesomorphic; n-Alkanoates