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Ionic Hydrogen Bonds (ionic + hydrogen_bond)

Distribution by Scientific Domains

Chemistry	100%

Selected Abstracts

Ionic Hydrogen Bonds Controlling Two-Dimensional Supramolecular Systems at a Metal Surface

CHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2007
Dietmar Payer
Abstract Hydrogen-bond formation between ionic adsorbates on an Ag(111) surface under ultrahigh vacuum was studied by scanning tunneling microscopy/spectroscopy (STM/STS), X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and molecular dynamics calculations. The adsorbate, 1,3,5-benzenetricarboxylic acid (trimesic acid, TMA), self-assembles at low temperatures (250,300,K) into the known open honeycomb motif through neutral hydrogen bonds formed between carboxyl groups, whereas annealing at 420,K leads to a densely packed quartet structure consisting of flat-lying molecules with one deprotonated carboxyl group per molecule. The resulting charged carboxylate groups form intermolecular ionic hydrogen bonds with enhanced strength compared to the neutral hydrogen bonds; this represents an alternative supramolecular bonding motif in 2D supramolecular organization. [source]

Ratiometric Fluorescence Sensing of Fluoride Ions by an Asymmetric Bidentate Receptor Containing a Boronic Acid and Imidazolium Group

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 18 2009
Zhaochao Xu
Abstract The synthesis of the first examples of anion receptors that utilize boron,fluoride interactions and (C,H)+···F, -type ionic hydrogen-bond interactions in the binding of F ions is reported herein. o -, m -, and p -Phenylboronic acids were linked to naphthoimidazolium through a methylene group. On the basis of fluorescence and 19F NMR studies, we have confirmed that the addition of fluoride to a boron center occurs prior to the formation of (C,H)+···F, -type ionic hydrogen bond with the imidazolium moiety. More importantly, these investigations have demonstrated that only the receptor bearing the ortho -directed boron and imidazolium exhibits enhanced fluoride binding. The increased binding ability of the asymmetric bidentate receptor of ortho -boronic acid and imidazolium towards F, enables it to sense fluoride ions in a 95:5 CH3CN/HEPES aqueous solution. The fluorescence responses to different anions were also explored; the ortho -boron-imidazolium receptor displayed ratiometric fluorescence changes and a high selectivity towards fluoride ions over other anions (Cl,, Br,, CH3CO2,, HSO4,, and H2PO4,).(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Vibrational spectral studies and the non-linear optical properties of a novel NLO material L -prolinium tartrate

JOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2006
L. Padmaja
Abstract Vibrational spectral analysis of the novel non-linear optical (NLO) material, L -prolinium tartrate (LPT) was carried out using NIR-FT-Raman and FT-IR spectroscopy. The density functional theoretical (DFT) computations have been performed at B3LYP/6,31G (d) level to derive equilibrium geometry, vibrational wavenumbers, intensities and first hyperpolarizability. The reasonable NLO efficiency, predicted for the first time in this novel compound, has been confirmed by Kurtz,Perry powder second-harmonic generation (SHG) experiments. The charge-transfer interaction between the pyrrolidine ring and the carbonyl group of the tartrate anion through the intramolecular ionic hydrogen bonds is confirmed by the simultaneous activation of ring modes in IR and Raman spectra. The splitting of the ring-breathing mode, pseudo-rotational ring puckering modes and the NH2 modes of the pyrrolidine ring lead to the conclusion that the pyrrolidine ring adopts a conformation intermediate between the envelope (bent) form and the half-chair (twisted) form, resulting in the lowering of symmetry from C2 to Cs. The lowering of the methylenic stretching wavenumbers and the enhancement of the stretching intensities suggest the existence of the electronic effects of back-donation in LPT. The positional disorder of the pyrrolidine ring, the presence of blue-shifting H-bonds as well as other non-bonded interactions in LPT, low frequency H-bond vibrations and the role of intramolecular charge transfer and the hydrogen bonds in making the molecule NLO active have been analysed on the basis of the vibrational spectral features. Copyright © 2006 John Wiley & Sons, Ltd. [source]