RESUMEN
A series of benzannulated N-heterocyclic compounds containing divalent 14 group atoms, C6H4(NR)2EII, E = C, Si, Ge, Sn, Pb, have been studied by various experimental (vibrational and UV-vis spectroscopy) and theoretical (NICS, ISE, ACID) techniques. The methods used confirm 10 π-electron delocalization (aromaticity) in these heterocycles, however, the aromaticity sequences estimated by the criteria based on different physical properties do not coincide.
RESUMEN
A disiladicarbene, (Cy-cAAC)2Si2 (2), was synthesized by reduction of Cy-cAAC:SiCl4 adduct with KC8. The dark-colored compound 2 is stable at room temperature for a year under an inert atmosphere. Moreover, it is stable up to 190 °C and also can be characterized by electron ionization mass spectrometry. Theoretical and Raman studies reveal the existence of a SiâSi double bond with a partial double bond between each carbene carbon atom and silicon atom. Cyclic voltammetry suggests that 2 can quasi-reversibly accept an electron to produce a very reactive radical anion, 2(â¢-), as an intermediate species. Thus, reduction of 2 with potassium metal at room temperature led to the isolation of an isomeric neutral rearranged product and an anionic dimer of a potassium salt via the formation of 2(â¢-).
RESUMEN
The structure and dynamic behaviour of monomeric lead(ii) dithiolate Pb(SCH(2)CH(2)NMe(2))(2) are studied by multi-nuclear NMR, IR and Raman spectroscopy in solution, as well as variable-temperature Raman spectroscopy and X-ray diffraction analysis in the solid-state, revealing an unusual dynamic "flip-flop" process in solution and reversible conformational isomerism of the chelated five-membered rings in the solid-state.
RESUMEN
Sublimation of sulflower, octathio[8]circulene C 16S 8 ( 1), on heating under high vacuum ( approximately 10 (-5) Torr) leads to successive formation of two modifications: a white film ( 1W) and a red polycrystalline solid ( 1R). When kept at room temperature for several weeks, 1W spontaneously turns pink, reflecting the monotropic phase transition 1W --> 1R. The accurate molecular and crystal structure of 1R has been studied using low-temperature (100 K) high-resolution single crystal X-ray analysis. The C 16S 8 molecule in crystal is strictly planar with nearly equalized bonds of each type (C-C, C-S, and CC). The point symmetry group of the free molecule is D 8 h , and the crystal space group is P2 1/ n. These data allowed group-theoretical analysis of vibrational normal modes to be accomplished. Investigation of the charge density distribution of 1R including Bader's AIM approach has revealed rather strong intermolecular S...S, S...C, and C...C interactions of charge transfer and pi-stacking types with overall lattice energy of 28.5 kcal/mol. The charge transfer due to the S...S interactions is the reason for the red coloration of 1R. The latter is reflected by its UV-vis spectrum exhibiting absorption bands in the visible region which are absent from that of 1W. Both modifications were studied comparatively by vibrational (Raman, IR) and electronic spectroscopies as well as XRD powder diffraction. All the results obtained are fully consistent and show that 1W is much less ordered than 1R with significantly weakened intermolecular interactions. Rationalizing of these results has led to an idea that 1W could be soluble, in contrast to 1R. Indeed, 1W appeared soluble in common solvents; this finding opens the way to the study of the chemistry of 1 and investigation of its electrooptical properties.
RESUMEN
Equatorial-axial isomerism of the tin(II)-iron(0) complex (Me2NCH2CH2O)2Sn-Fe(CO)4 (), which indicates that the free Sn(OCH2CH2NMe2)2 () ligand can behave as a stannylene, has been revealed and studied by NMR and IR spectroscopy in solution as well as by Raman spectroscopy and X-ray diffraction analysis in the solid-state.
RESUMEN
For the stable germylene, N,N'-di-tert-butyl-1,3-diaza-2-germacyclopent-4-en-2-ylidene, 2, the Raman line for the cyclic C=C stretching mode is strongly enhanced and shifted to longer wavelength, compared with that in reference compounds. The enhancement and frequency shift are even greater than those found for the corresponding stable silylene 1. These results, along with NMR evidence and theoretical calculations, suggest that the aromatic electron delocalization is even greater in the germylene than that in the silylene.
RESUMEN
The UV-Vis, pre-resonance Raman and IR spectra of the complex (Cy3P)2Pt=SiMes2 (1) were obtained as well as Raman spectra of some model compounds. The experimental data and the results of normal coordinate calculations show that the stretching vibration of the Si?Pt bond in 1 is not localized, the nuSi=Pt internal coordinate makes significant contribution to two normal modes with frequencies at 465 and 612cm-1, whose Raman intensity is enhanced by pre-resonance.
Asunto(s)
Platino (Metal)/análisis , Compuestos de Silicona/análisis , Espectrometría Raman/métodos , Carbono/análisis , Oxígeno/análisis , Silicio , Rayos UltravioletaRESUMEN
New stereoregular cyclic polysilanols of the general formula [PhSi(O)OH]n (n = 6 and 12) have been selectively obtained in high yields by the reaction of cagelike oligophenylmetallasiloxanes with dilute solutions of hydrochloric acid at low temperatures. An alternative method was used to prepare cis-[PhSi(O)OH](4) from sodium phenylsiloxanolate, cis-[(Na(+))(4)[PhSi(O)O(-)](4)].(1-butanol)(x). All compounds were fully characterized by NMR and IR spectroscopy and molecular weight determinations. The structure of cis-[PhSi(O)OH](6) was confirmed by single-crystal X-ray analysis. Furthermore, a series of stereoregular cyclosiloxanes containing triorganylsiloxy groups at each silicon atom was prepared by the reactions of the cyclic polysilanols with triorganylchlorosilanes Me(3)SiCl, Me(2)ViSiCl, and Me(2)(CH(2)Cl)SiCl.