Inhaltszusammenfassung

The stannocanes mentioned in the title have been synthesized from MeSnHal(3) and (HSCH2CH2)(2)X. Crystal structure determinations and vibrational transitions of the coordination polyhedra around tin are given. The 12 compounds are compared with the 9 compounds Cl-2/Br-2/I-2-Sn(SCH2CH2)(2)X (X = NMe, O, S) investigated in a previous study. Apart from one molecule with heptacoordinated tin, the other compounds comprise pentacoordinated tin on a ''path'' from a tetrahedron to a trigonal bipyrami...The stannocanes mentioned in the title have been synthesized from MeSnHal(3) and (HSCH2CH2)(2)X. Crystal structure determinations and vibrational transitions of the coordination polyhedra around tin are given. The 12 compounds are compared with the 9 compounds Cl-2/Br-2/I-2-Sn(SCH2CH2)(2)X (X = NMe, O, S) investigated in a previous study. Apart from one molecule with heptacoordinated tin, the other compounds comprise pentacoordinated tin on a ''path'' from a tetrahedron to a trigonal bipyramid. The path is discussed in terms of the molecular orbitals of the three-center, four-electron interaction X...Sn-Cl/Br/I/Me. By the use of standard single-bond distances, vibrations, and bond energies, and with the help of Morse potentials, the structural and vibrational data are transformed into semiquantitative energy diagrams of the occupied equatorial and axial orbitals. The energy differences between these orbitals and those of a tetrahedral configuration are added up to give the total energy gain of each compound (energy coordinate) and are plotted versus an angle sum of the respective trigonal bipyramid (configurational coordinate). The total energy gain from the structural and vibrational data includes an energy contribution fi om the LUMO of the three-center interaction. A model is presented in which an enhanced electronegativity of the equatorial and axial ligands inhibits the formation of a pentacoordinate structure. The drive for pentacoordination (sigma-Lewis acidity) results from a movable charge which populates the LUMO (pi-Lewis acidity). The movable charge originates from the lone pairs of the halides and chalcagenides, from the pi-electrons of aromatic rings, or from the hyperconjugation in the case of the methyl group. This model contradicts the generally accepted opinion that electronegativity promotes pentacoordination. With regard to the presented model, a short discussion of hypervalency for the other group 14 elements and a mention of the broad subject of bimolecular nucleophilic attack are given. » weiterlesen» einklappen

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