5-mercapto-1,3,4-thiadiazole-2yl carboxylic derivatives adsorbed on silver nanoparticles

Monica M. Venter1, Simona Cinta Pinzaru2, Vasile Chis2, Vasile N. Bercean3, 
Ionel Haiduc1 Andrei Patrascu2

1 “Babes-Bolyai” University, Faculty of Chemistry and Chemical Engineering, Department of Inorganic Chemistry, Arany Janos 11, Cluj-Napoca, Romania.
2 “Babes-Bolyai” University, Faculty of Physics, Department of Molecular Spectroscopy, Kogalniceanu 1, Cluj-Napoca, Romania.
3 "Politehnica" University, Faculty of Industrial Chemistry and Environment Engineering, Department of Organic Chemistry, Bocsa 1, Timisoara, Romania.

Heterocyclic mercapto-aza derivatives were successfully used in the design of channel-type supramolecular structures revealing catalytic and separation properties, similar to zeolites. The design of such non-conventional microporous materials involves molecular self-assembly through E-HE (E = N, S) and/or SS interactions.1,2 In view of recent interest in this field, we initiated the FT-IR and FT-Raman investigations of new 5-mercapto-1,3,4-thiadiazole-2yl carboxylic acids and related esters (A-B), containing an extensive number of N/NH, S/SH and O/OH species as well as exocyclic alkyl spacers.3,4

A 					B

	The aim of this work is to extend these investigation with complete Raman and surface enhanced Raman spectroscopy (SERS) in conjunction with Density Functional Theory (DFT) calculations, in order to establish the tautomeric forms of A-B and the most probable intermolecular interactions in solid state. In the case of the acids, the DFT calculated frequencies of the dimers have been found in better agreement with the corresponding experimental counterparts than those calculated for the monomers. Moreover, the adsorption behavior on the nanometric scale silver surface was analyzed. A strong chemisorption of these compounds was concluded and the orientation geometry was discussed. 
	Both theoretical and experimental data suggest that the title compounds are present in solid state mostly in the tione tautomeric form and the dimers form through double O-HO and / or N-HS intermolecular interactions.

1.	V. Berceanc, C. Crainic, I. Haiduc, M.F. Mahon, K.C. Molloy, M.M. Venter, P.J. Wilson, J. Chem. Soc., Dalton Trans., 1036, 2002.
2.	C.N.R. Rao et al, J. Amer. Chem. Soc, 119, 10867, 1997; J. Mater. Chem, 9, 2407, 1999; J. Amer. Chem. Soc, 121, 17521, 999.
3.	M.M. Venter, S. Cinta-Pinzaru, V. Bercean, I. Haiduc, Studia Univ. BB, Physica XLYX, 3, 285, 2004.
4.	M.M. Venter, S. Cinta-Pinzaru, V. Chis, V. Bercean, I. Haiduc, in Perspectives in Vibrational Spectroscopy, Eds. V.K. Rastogi, 2006, in press.