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Structure of triazole compounds on Ag surface - Raman, SERS, XPS spectroscopy and DFT calculations.
|Beata Wrzosek , Janusz W. Cukras , Jolanta Bukowska|
Warsaw University, Faculty of Chemistry, Pasteura 1, Warszawa 02-093, Poland
Molecular structure of 1,2,4-triazole (T), 3-amino-1,2,4-triazole (AT), 3-merkapto-1,2,4-triazole (MT) and 3-amino-5-merkapto-1,2,4-triazole (AMT) adlayers on silver surface was investigated with surface-enhanced Raman (SERS), Raman Scattering and X-ray photoelectron (XPS) spectroscopy and DFT calculations.
To analyze the results, a comparison between the Raman spectra of concentrated, alkalized and natural triazole solutions in H2O and D2O and the SERS spectra of adlayers formed in these solutions, measured in situ and in pure NaOH solutions and Raman spectra of sediment precipitated from natural, concentrated triazole solutions after adding AgNO3 have been recorded. These experiments revealed that in adlayers of T the molecules exist as a triazole anions, while AT adlayers contain imino form of molecules deprotonated in the ring . In both monolayers orientation of the ring is more or less parallel to the metal surface. Chemical state of MT and AMT molecules and the monolayer structure depend on monolayer environment. In the sufficiently high concentration and/or low enough pH value of solutions hydrogen atom attached to the pyrrole nitrogen atom is retained and the ring orientation is more or less perpendicular to the metal surface. A decreased concentration and/or an increased pH value of the solution are favourable to the ring deprotonation and in case of AMT also the transformation into the imino form. The change of the ring orientation into more parallel with respect of the metal surface is accompanied by these transformations of the chemical state. XPS spectra proved the existence of an Ag-S bond in all conditions in monolayers of both compounds.
The spectroelectrochemical experiments have also revealed the potential dependence of the structure of triazole monolayers on the electrode. As the changes of chemical state and structure are reversible, the MT and AMT monolayers can be used as a molecular switch.
Quantum mechanical calculation of the vibration energy of triazole- Ag complexes has allowed assigning their SERS spectra.
Presentation: Poster at SMCBS'2009 International Workshop, by Beata Wrzosek
See On-line Journal of SMCBS'2009 International Workshop
Submitted: 2009-08-31 14:21 Revised: 2009-08-31 14:38