Hypercoordinated Carbon in 2,8,9-Sila- and Thia-Substituted Carbatranes

Ab initio methods demonstrate that internally protonated forms (a) of the molecules of carbatranes XC(SiH2CH2CH2)3N (X = H, F) are significantly more favorable than their externally protonated forms (b). The quantum-topological AIM approach suggests that the main reason for that is the formation of a medium-strength hydrogen C···H+N bond unknown previously in the silacarbanyl cations a

Rhizobacteria Effect on Arsenic Migration and Translocation of Biogenic Elements in Plants

The study was aimed at the transformation of arsenic compounds in the rhizosphere, its accumulation in plants, P and Si translocation to plants under the influence of Bacillus megaterium var. phosphaticum, and Bacillus mucilaginosus with various forms of As compounds in the soil. The authors describe the maximum effect of Bacillus megaterium var. Phosphaticum strain on As migration, its mobilization and immobilization in the rhizosphere due to arsenic leaching from mineral and difficult-todestroy compounds and its accumulation in plants. The forms of arsenic compounds were isolated from the rhizosphere based on sequential extraction procedures. The features of the inter-element As-P interaction in plants were established. With the intense accumulation of As in the rhizosphere inoculated with rhizobacteria, the intake of phosphorus into plants was not observed, as contrary to Si. The study of As and biogenic elements behavior under the influence of rhizobacteria is of great importance in the development of ecobiotechnologies related to soil remediation and crop production

Radical cations of phenyl silatrane

International audienceElectrochemical oxidation of phenylsilatrane (1) in CH3CN/0.1 M Bu4NPF6 has been studied by voltammetry, UV-Vis and EPR-coupled spectroelectrochemistry supported by DFT calculations. One-electron withdrawal from the HOMO of 1, formed with a predominant contribution of the atrane N atom to the 3c-4e system, results in a short lived radical cation, in which the atrane nitrogen atom is almost planar and carries most of the spin density showing strong coupling with the protons of the axially directed C-H bonds of the three adjacent α-methylene groups (g = 2.0037, aαHax = 37.93 G, aαHlat = 0.23 G and aβH = 1.8 G). EPR spectroscopy and DFT calculations attest that the unpaired electron in the radical cation does not reside at the Si atom. © 2017 The Royal Society of Chemistry

Hypervalent benzophenones

International audienceBenzophenones (BPs) of the type 2-R-BP and 2,2'-R-BP, carrying silicon-or germanium-containing substituents R (R = EY2X; E = Si, Ge; Y = H, Me, F, Cl; X = H, F, Cl, OTf) at one or at two ortho-positions of the arene rings, were theoretically designed. Among 26 compounds considered, only 10 monosubstituted 2-R-BP and 5 bis-substituted 2,2'-R-BP (in hexane and DMSO solutions) belong to the first examples of hypervalent benzophenones. In these "true" chelates, the length of the O -> E dative contact (which has a covalent component, according to the AIM analysis) is in the range of 2.0-2.4 angstrom, and the degree of pentacoordination of E is higher than 40%. In these compounds, a significant planarization of the benzophenone part occurs, compared to the initial BP. The TD-DFT calculations suggest the UV spectral properties of the hypervalent BPs to differ fundamentally from those of BP. For the "true" chelates 2-R-BP and 2,2'-R-BP, there is a well pronounced trend of a change of the coordination O -> E contact strength along with the difference between the wavelengths of their first high-intensity band and the pi pi* band of the unsubstituted BP. (c) 2018 Elsevier B.V. All rights reserved

Molecular Design of Hypercoordinated Silacyclophanes

MP2 and DFT (B3LYP, M06-2X) methods using the 6-31G(d) and 6-311++G(d,p) basis sets are applied to the investigation of the structure of a wide series of silacyclophanes XSi[Y(CH₂)_<i>n</i>]₃C₆R₃ <b>1</b>–<b>9</b> (X = <i>t</i>-Bu, Me, NH₂, F, OTf; Y = O, NH, CH₂; R = H, SiH₃, Li; <i>n</i> = 1, 2). The molecules studied exist exclusively in the <i>out</i>-<i>C</i>₃-symmetric form (for X = NH₂, OTf the symmetry is not strict). Identification of the presence and estimation of the extent of the hitherto unknown Si···Ar multicenter intramolecular interaction of the tetracoordinate silicon atom with the π-system of the benzene ring in <b>1</b>–<b>9</b> was performed by analysis of geometric parameters, using the methods of Δδ ²⁹Si coordination shift, NICS(1) values, and the results of the AIM, NBO, and MO analyses. In molecules XSi[YCH₂CH₂]₃C₆R₃ <b>1</b>–<b>4</b>, irrespective of the nature of X, Y, and R, the multicenter interaction Si···Ar is weak. This interaction is strongly enhanced in compounds XSi[YCH₂]₃C₆R₃ <b>5</b>–<b>9</b>, with side chains shortened by one methylene group. The variation of geometric (<i>d</i>_Si–Ar, Δ_Si, η_α), electronic (∑δ(Si,C)), orbital (∑Δ<i>E</i>⁽²⁾[π_C–C→σ*_Si‑X]), and NMR (Δδ ²⁹Si) characteristics of the coordination center XSiY₃Ar in <b>5</b>–<b>9</b>, caused by varying the environments of the silicon atom and of the arene fragment, is typical for pentacoordinate silicon compounds

Hypercoordinated Carbon in 2,8,9-Sila- and Thia-Substituted Carbatranes

Ab initio methods demonstrate that internally protonated forms (a) of the molecules of carbatranes XC(SiH2CH2CH2)3N (X = H, F) are significantly more favorable than their externally protonated forms (b). The quantum-topological AIM approach suggests that the main reason for that is the formation of a medium-strength hydrogen C···H+N bond unknown previously in the silacarbanyl cations a.Reprinted (adapted) with permission from Organometallics 26 (2007): 4568, doi:10.1021/om700306x. Copyright 2007 American Chemical Society.</p

Isomer-selective dative bond O -&gt; M (M = Si, Ge) for designing new photochromic hemi-indigo systems

International audienceNew photochromic systems MY2X-HI (M = Si, Ge) were designed (at the DFT level of theory) by replacing the hydrogen atom in the nitrogen of the pyrrole ring of hemi-indigo, HI, with silyl- or germyl-substituents. The E isomers of MY2X-HI contain a dative bond O -&gt; M (pentacoordinated atom M) both in the ground S-0 and in the excited S-1 states. This leads to a significant difference in the absorption and fluorescence maxima (lambda(fl) - lambda(abs)) of the Z and E forms of hypervalent hemi-indigos; this difference is more than twice that of the parent HI. There is a trend to increasing separation of first pi -&gt;pi* absorption bands of the E and Z isomers of MY2X-HI with the increase in their relative stability. (C) 2021 Published by Elsevier B.V