S. S. Bukalov

Raman evidence of aromaticity of the thermally stable silylene (tBuNCHCHNtBu)Si

Abstract The Raman, IR and UV spectra of the silylene ( t BuNCH CHN t Bu)Si: ( 1 ) as well as the Raman spectra of related compounds with tetravalent silicon ( t BuNCH CHN t Bu) 2 Si ( 2 ) and ( t BuNCH CHN t Bu)SiCl 2 ( 3 ) and of the heterocycle ( t BuNCH CHN t Bu)C O ( 4 ) are reported. Comparison of the spectra obtained for 1 – 3 reveals a lowered frequency and greatly enhanced intensity of the Raman band corresponding to the C C stretching vibration in the spectrum of 1 which is in accord with the aromatic character of the silylene.

VIBRATIONAL SPECTRA OF DISILENES. NORMAL COORDINATE ANALYSIS AND IDENTIFICATION OF THE V(SI=SI) STRETCHING VIBRATION

Abstract Experimental vibrational spectra are reported for three carbon-substituted disilenes along with data on normal coordinate analysis of several simplified disilene models. Calculations show that there is no normal mode in the disilene spectrum which is well-localized in the Si=Si bond. The Si=Si and Si-C stretching coordinates are heavily mixed. Their in-phase combination results in a normal mode with frequency in the region 450–550 cm −1 which manifests itself as a Raman line of variable intensity (the so-called v (Si=Si)). Their out-of-phase combination gives a mode in the region of about 700 cm −1 which shows itself as an intense Raman line (the so-called v S (Si-C)). Vibrations of an aromatic ring, if present in a disilene molecule, can also couple with the v (Si-Si). Particular eigenvector elements of the two modes in question and thus their potential energy distributions strongly depend on the structure and symmetry of a given disilene molecule. However, the contribution of the Si=Si stretching coordinate to the normal coordinate with frequency in the region 450–550cm −1 is always significant, justifying the designation of this mode as the v (Si=Si).

Vibrational spectra and structure of trimethylindium and trimethylthallium

Abstract A detailed vibrational spectrum of trimethylthallium is reported for the first time (Raman spectra of the melt and crystal, IR spectra of crystalline, gaseous and matrix-isolated samples). Analogous data were also obtained for trimethylindium for comparison. In the Raman spectra of both compounds in the liquid state some peculiarities are found which suggest low-barrier hindered rotation of the methyl groups. Some features in the spectra of trimethylthallium and triethylthallium distinguish these compounds from their In and Ga analogues, and could be interpreted as arguments in favour of distortion of the planar TIC 3 skeleton in condensed phases, probably as a result of the pseudo-Jahn—Teller effect.

Raman study of order-disorder phase transitions in polydialkylmetallanes of the type [R2M]n: organometallic polymers with the main chain consisting entirely of either Si, or Ge, or Sn atoms

Variable-temperature Raman studies were carried out for some representatives of a novel class of industrially promising (sigma) -conjugated polymers-polymetallanes of the type (R2M)n, M equals Si, Ge, Sn. Electronic-conformational nature of the thermochromic phase transitions of order- disorder type exhibited by some of these polymers was investigated. The applicability of Shorygins semi-classical approach to the pre-resonant Raman intensity enhancement was confirmed experimentally by the example of polysilanes.

Probing the structure of the silylene complex (Cy3P)2Pt=SiMes2.; UV-Vis and pre-resonance Raman investigations.

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.

The structure and phase transitions of crystalline polydimethylsilane (Me 2 Si) n revisited

The results of vibrational spectroscopy and X-ray diffraction obtained at the present level of the methods confirm the planar trans (all-A) conformation of the polydimethylsilane chain recently called in question. The differential scanning calorimetry data also verify the first order phase transitions at about –35 and 145 °C which proceed with retention of the all-A chain conformation and are of order-disorder type.

Vibrational spectra and electronic structure of 11-vertex boron-containing clusters: a comparative study of [B11H11]2–, [CB10H11]–, and C2B9H11

Vibrational spectroscopy studies of 11-vertex boron-containing clusters [B11H11]2–(1), [2-CB10H11]– (2), and 2,3-C2B9H11 (3) revealed two low-frequency large-amplitude modes in their spectra and, therefore, structural nonrigidity of these polyhedra in contrast to related 12-, 10-, and 6-vertex closo-clusters. The nonrigidity originates from specific features of the electron density distribution. According to calculations within the framework of the Atoms in Molecule (AIM) theory, these polyhedra are characterized by the lack of many bond paths localized on corresponding edges, in particular, between boron atoms with coordination numbers of 6 and 5 (6k and 5k). Consequently, these polyhedra are composed of not only trigonal faces, i.e., formally do not have the closo-structure that was traditionally ascribed to them based on formal count of (2n + 2) valence electrons. According to calculations of three-center delocalization indices, the absence of bond paths is not equivalent to the lack of interaction between corresponding atoms since this interaction occurs through open three-center bonds. The mechanism and reasons for signal averaging observed in 11B NMR spectra of compounds 1 and 2 in contrast to 3 are analyzed.

Normal coordinate analysis of disilenes and diphosphenes. The ν(SiSi) and ν(PP) stretching vibrations

Abstract Normal coordinate analysis (NCA) of some disilene and diphosphene molecules has been performed and compared with NCA of corresponding alkenes. For various models of disilenes containing the C 2 Siue5fbSiC 2 moiety, NCA shows that Siue5fbSi and Siue5f8C stretching coordinates are heavily mixed, their in-phase combination resulting in a normal mode in the region 450–550 cm −1 , while their out-of-phase combination is in the region 600–750 cm −1 . In contrast, the results of NCA for diphosphenes show that the vibration at ≈ 600 cm −1 is well localized, being predominantly νPue5fbP stretch (≈ 90% in PED).