Small chalcogen-organyls - fundamental structural, conformational and electronic properties

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Thinking in functional groups is one of the most successful concepts in chemistry. A detailed understanding of their properties is therefore at the heart of this subject. The overall aim of this German-Argentinean collaboration project is to gain detailed knowledge of structural and physical properties of fundamental model compounds, in which chalcogen-functional groups are bonded to small alkyl or silyl groups with variable electronic properties. This allows investigating small structural units in isolation of other effects and applying a multi-method approach. The project focuses on changes in structure, conformation and spectroscopic pro-per¬ties depending on electronic variation of the substituents, but also on the phase (gas/liquid/solid). An understanding of intramolecular effects, including anomeric (stereo-electronic), steric, mesomeric and inductomeric effects as well as intermolecular interactions are the main objectives. The objects of study include thiocyanates (RSCN) and isothiocyanates (RNCS), sulfenylcarbonyls (RSC(O)X) disulphides (RSSR), thionitrites (R-SNO), perfluoroalkylsulfinyl (RS(O)X) and -selenyl (RSe(O)X) compounds, perfluoroalkylthiocarbonyl (RS(S)X) and perfluoroalkanoyl halides of the type (RC(O)X), with a systematic evaluation of substituent effects, i.e. R = alkyl, perfluoralkyl, and various silyl and X = halogen, parahalogen, methoxy or pseudohalogen substituents (F, Cl, Br, CN, I, N3, CF3, CH3O). The methodology is based on determination of molecular struc¬tu¬res in the gas and solid phases (by means of gas electron-diffraction, vibrational spectroscopy including matrix isolation spectroscopy, in-situ crys¬tallisation & X-ray diffraction, electron density determination and topology analysis), backed by simul¬ta¬ne¬ous comparison with computational results. Cooperation with partners from Hannover and Beijing allows additionally performing microwave, gas-phase UV-vis, photoelectron spectroscopy and photoionization mass spectrometry investigations, hence providing further information on structure and bonding. In selected cases LNLS (Brazil) and SOLEIL (France) synchrotron facilities may be used to gain knowledge from their available atomic spectroscopies. This true multi-method approach gives rise to a very potent and creative synergy of both experimental information and theoretical models and assures the reliability of results and a high-level multifaceted understanding of bonding and interactions of important reference compounds.