Tetraaryl-methane analogues in group 14—V. Distortion of tetrahedral geometryin terms of through-space π–π and π–σ interactions andNMR sagging in terms of π–σcharge transfer |
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Authors: | Michael Chariss , Andrea Zickgraf, Heike Stenger, Elmar Br u, Cristelle Desmarquet, Martin Dr ger, Silke Gerstmann, Dainis Dakternieks,James Hook |
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Affiliation: | Michael Charissé, Andrea Zickgraf, Heike Stenger, Elmar Bräu, Cristelle Desmarquet, Martin Dräger, Silke Gerstmann, Dainis Dakternieks,James Hook |
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Abstract: | 44 members of thecompound series Ph4−nMRn (M=Si, Ge, Sn, Pb; R=o-, m-, p-Tol; n=0–4) were synthesized (15 newcompounds). The crystal structures of Ph3Sn (o-Tol) and PhSn (o-Tol)3 were determined and compared to 16 known structures. Subject to the distanced (M–C), an interplay between through-space π–π repulsion and π–σ attraction leads to either elongated or compressed tetrahedral geometry. 29 Si-, 119 Sn- and 207 Pb-NMR chemical shifts were determined in solution and in the solid state. 73 Ge chemical shifts were measured only in solution. Anupfield or downfield sagging of the chemical shifts along each series is rationalized in terms of a π–σcharge transfer which is constrained by torsion of the aromatic groups. |
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Keywords: | silicon germanium tin lead through-space interaction heteronuclear NMR in solution and solidstate pi ndash sigma ast charge transfer |
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