No abstract

Molecular and lattice structures of a homologous series (n(c) = 8-20, inclusive) of silver (I) n-alkanoates are determined from X-ray Powder Diffraction, Solid State spin decoupled (13)C-NMR and variable temperature Fourier Transform Infrared Spectroscopies. The compounds crystallize in a monoclinic crystal system with hydrocarbon chains in the fully extended all-trans conformation. Moreover, the chains are tilted ca. 75° with respect to the metal basal plane and are arranged as methyl(tail)-to-methyl(tail) bilayers within a lamellar. The methyl chain ends, from different layers in the bilayer, do not overlap but are in such close proximity to cause methyl-methyl interactions. In a molecule, two carboxylate groups bind in a syn-syn type bridging bidentate mode to two silver atoms to form an eight-membered structure. Intramolecular silver-silver and intermolecular Ag-O-Ag interactions stabilize the head group and promote the formation of layer type polymeric sheets. Though the compounds are nearly isostructural, odd-even chain alternation is observed in density, anti-symmetric stretching vibrations of methyl and unusually, carboxylate (head) groups, as a result of packing differences of hydrocarbon chains within the crystal lattice. These arise from the relative vertical distances between polymeric sheets, which are not in the same plane. Thus, for odd chain length compounds, where those distances are less than for even chains, more ordered packing and hence higher densities are observed for these adducts. Also, the numbers and natures of the thermotropic phase transitions are chain length dependent and irreversible.

Investigations on the phase behaviors and structural properties of mono-, di-and poly-valent metal carboxylates are reviewed with reference to developments in experimental and theoretical concepts surrounding their liquid crystalline properties. The main methods of structural investigation such as X-ray diffraction, infrared and 13 C-NMR spectroscopies are examined in detail on the basis of common synthetic routes leading to the isolation of pure compounds. A detailed review of the thermal behaviors of several metal carboxylates is presented along with proposed theories and molecular models for odd-even alternation, chain length effects, phase structures and mesophase formation. Theories explaining the effects of metal ion radii and chain unsaturation are also discussed. Proposed degradation mechanisms resulting in the formation of various products and kinetic studies are also considered. Though this review highlights a number of investigations on the structural and phase properties of the mostly widely studied carboxylates, the results presented here strongly indicate that there is room for further studies on some of these systems.

Effective control of chemistry at interfaces is of fundamental importance for the advancement of methods of surface functionalization and patterning that are at the basis of many scientific and technological applications.Aconceptually new type of interfacial chemical transformations has been discovered, confined to the contact surface between two solid materials,w hichm ay be induced by exposure to X-rays, electrons or UV light, or by the application of electrical bias. One of the reacting solids is aremovable thin film coating that acts as ar eagent/catalyst in the chemical modification of the solid surface on which it is applied. Given the diversity of thin film coatings that mayb eu sed as solid reagents/catalysts and the lateral confinement options provided by the use of irradiation masks,c onductive AFM probes or stamps,a nd electron beams in such solid-phase reactions,t his approach is suitable for precise targeting of different desired chemical modifications to predefined surface sites spanning the macroto nanoscale.Recent exploratory experiments conducted by us with the purpose of devising acomprehensive methodology of surface chemical functionalization and patterning led to the rather surprising discovery that the top CH 3 groups of highly ordered OTSmonolayers (monolayers self-assembled from n-octadecyltrichlorosilane precursor molecules,S iCl 3 À(CH 2 ) 17 À CH 3 ) [1, 2] may be quantitatively converted to COOH with full preservation of the composition and structure of the monolayer hydrocarbon core using various thin-film coatings as oxidizing reagents.T he conversion of OTSi nto OTSox (surface-oxidized OTS) is implemented upon exposure of the coated OTSm onolayer to different sources of electromag-netic radiation or electrons (see Scheme 1f or some representative examples). Reaction route (a) in Scheme 1w as discovered by accident in experiments involving electron beam (e-beam) deposition of different metals (Ag, Al, Au,Ti) on OTSm onolayers on silicon (OTS/Si) or quartz (OTS/Q) covered with 4-10 nm-thick PVA( polyvinyl alcohol) film coatings.D epositing the same metals (under identical experimental conditions) on bare OTS monolayers did not affect their composition and structure in any measurable manner, whereas using at ungsten target in the e-beam evaporator operated under conditions below the threshold evaporation of this metal was found to convert OTSinto OTSox as in the actual deposition of metals on the PVAsurface.Finally,using thermal instead of e-beam metal deposition on PVA-coated OTSm onolayers did not affect their composition and structure either.T hese observations suggested that, in the presence of as ource of oxygen (here the thin PVAc oating), the surface oxidation of OTSisinduced by the radiation that accompanies the metal evaporation in e-beam evaporators (X-rays,s econdary and scattered electrons and UV light, emitted when energetic electrons strike am etal target) [3] rather than by the metal deposition itself.T hat each of the different components of this radiation may induce ...

No abstract