Carboxylate−Counterion Interactions and Changes in These Interactions during Photopolymerization of a Long-Chain Diacetylene Monocarboxylic Acid at Air−Water Interfaces:  External Infrared Reflection Absorption Spectroscopic Study

Abstract

External infrared reflection absorption spectroscopy was used to study the carboxylate-counterion interactions and changes in these interactions during the photopolymerization of a long-chain diacetylene monocarboxylic acid, 10,12-pentacosadiynoic acid (DA), at air-water interfaces in the presence of divalent metal ions, Ba 2+ (pH 7.7), Cd 2+ (pH 6.8), and Pb 2+ (pH 6.0). Upon reducing the molecular area (0.80 f 0.18 nm 2 /molecule), the DA monolayer on each subphase exhibited discrete frequency changes of an IR band due to a carboxylate antisymmetric stretching vibration (ν as (COO -)), indicating discrete changes in the coordination and/or association states of the carboxylate groups. Ab initio molecular orbital calculations were applied to confirm the empirical relationships between the frequency differences of the asymmetric and symmetric stretching bands of the carboxylate group and the modes of coordination of the group to metal ions. On the basis of the relationships, it was proposed that, when the molecular area is reduced, the carboxylate group in the DA monolayer on the Ba 2+ subphase changes its coordination mode from a bridging state to a bidentate one, while the carboxylate group in the DA monolayer on the Cd 2+ subphase keeps a bidentate coordination state. It was also suggested that the DA monolayer on the Pb 2+ subphase exhibits a coordination change from a bridging to bidentate state upon compression. IR spectral changes in the ν as (COO -) and ν s (COO -) regions observed during UV-irradiation-induced polymerization of the DA monolayers were similar to the IR spectral changes observed by compressing the monolayers without irradiation. The results indicated that the polymerization induces more densely packed states of the carboxylate groups in the monolayers.

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

“…Monodentate mode of coordination, where only one carbonyl oxygen atom interacts with the metal, due to its lower symmetry than the free ion shows similarities with the spectra of the monomeric form of carboxylic acids. Thus, for monodentate coordination, the asymmetric COO − stretching frequency increases while the symmetric COO − stretch decreases relative to the values observed for free carboxylate ion (Ohe et al 1999). For monovalent silver carboxylates, an opposite effect is observed with a significant lowering of the asymmetric COO − stretching position and generation of Δν as low as 103 cm −1 .…”

“…It was found that for bivalent metal cation coordination ability, Δν weakens in the order of monodentate, bridging/ionic bidentate to chelating bidentate form (Ellis et al 2005; Ohe et al 1999). The larger band shift for the complex indicates a larger unsymmetrical interaction between the metal ion and the carboxylate group.…”

Copper‐Coordinated Histidyl Bolaamphiphile Assembly as an Oxidative Catalyst: Coordination Structure and Catalytic Activity in Cyclohexane Oxidation

“…Simultaneously, the antisymmetric stretching peak of the carboxylate groups was up-shifted to 1614 cm À 1 from 1591 cm À 1 . The invariant Δ value implies that monodentate coordination of copper by the carboxylate moieties was dominant until the equimolar HisC7/ Cu ratio was exceeded; [30] the coordination state changed gradually with further increases in HisC7 content. The peak shifts indicate that not only the imidazole moieties but also the carboxylate moieties coordinated at copper ions.…”

Thermal and photochemical characteristics of silver 4-(4-nitrophenyl)butyrate revealed by infrared and Raman spectroscopy

“…In addition, referring to the empirical relationship between the frequency difference of the carboxylate stretching bands [13][14][15], that is, Dn ($170 cm À1 ) = n as (COO À )-n s (COO À ) and the types of bonding, the binding state of the carboxylate group to silver in Ag-4NPB is presumed to be a bridging one. Previously, a bridging bond was also assumed for Ag-STA and Ag-4NBA, but the Dn value for Ag-4NBA was 190 cm À1 , while the value for Ag-STA was at best 100 cm À1 .…”