Theories and experimental investigations of the structural and thermotropic mesomorphic phase behaviors of metal carboxylates

Abstract

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.

Synthesis and characterization of silver nanoparticles from (bis)alkylamine silver carboxylate precursors

“…Interaction of amine with silver carboxylate can be considered taking into account changes in the oscillation energy of the carboxyl group (Nelson and Taylor 2014). The type of coordination of carboxylate to metal cations is a consequence of changes in the CO bond lengths and the OCO angle.…”

Powder X-ray diffraction, infrared and 13C NMR spectroscopic studies of the homologous series of some solid-state zinc(II) and sodium(I) n-alkanoates

“…Hence, the chemistry of metal carboxylates has, for several decades, been investigated by various groups, resulting in the publication of several hundred articles. However, in recent times there has been a resurgence of research interest in these compounds, mainly because they exhibit diverse coordination and solid-state molecular packing characteristics which significantly affect their physico-chemical properties [1][2][3][4]. For example, the luminescence properties of some metal carboxylates point to possible application in luminescence display devices.…”

“…Also of interest is the fact that some metal carboxylates transition through a number of pre-melting phases, some of which are solid-solid whilst others are liquid crystalline phases of diverse physico-chemical properties when heated from the room temperature solid to the melt [4,[8][9][10]. Some metal carboxylates tend to form liquid crystals of the smectic C, SmC [11,12], type hence, they find application in Liquid Crystal Display devices, LCDs.…”

Chain Length and Thermal Sensitivity of the Infrared Spectra of a Homologous Series of Anhydrous Silver(I)n-Alkanoates

“…1472 cm −1 , associated with methylene ( CH 2 ) bending mode. For instance, splitting of this band due to intermolecular interactions between closely spaced alkyl chains is observed for monoclinic packing whilst a sharp band is indicative of triclinic arrangement where such interactions are less significant [17,21]. Interestingly, for the compounds discussed here, this band is not split (Figure 1) but is quite broad (Full width half maximum, FWHM: >10 cm −1 ) with a low frequency shoulder.…”

“…These bands, formed as a result of complete resonance in the carboxyl moieties due to coordination with the metal, show significant structural sensitivity; hence, they are extensively used in the literature for the characterization of metal-carboxyl coordination and symmetry [11][12][13][14][15]. For example, the difference in stretching frequencies between these two vibrations, Δ] = ] as − ] s , is related to the type of metal-carboxyl bonding; that is, if Δ] ≈ 100 cm −1 , chelating coordination is indicated but for those in the region of 150 to 170 cm −1 , bridging bidentate bonding is likely [17][18][19]. However, values in excess of 200 cm −1 indicate that the C-O bonds are highly asymmetric; thus coordination is monodentate.…”