Search

The structures of the three dimeric cyclotrisilicate anions [Si6O17]10−, [Si6O16]8− and [Si6O15]6− forming part of the compounds Rb10[Si6O17] or Rb14[Si4][Si6O17], Cs8[Si6O16] and Na3Y[Si6O15], respectively, have been described as different ways of condensing the more elemental cyclotrisilicate anions [Si3O9]6− [Hlukhyy & Fässler (2013). Z. Anorg. Allg. Chem. 639, 231-233]. Such a description prevents a rational explanation of the connectivity between the Si atoms. So, in this article the Si skeletons of the above silicate anions are put on a common basis in light of the extended Zintl-Klemm concept. Their connectivity is directly related to the ratio Ψ-S/Ψ-P resulting from the number of electrons transferred from the electropositive Na, Y, Rb and Cs atoms, offering a new example of the fact that there exists a univocal link between chemical composition (in terms of pseudo-atoms) and structure: the generalized Zintl-Klemm concept. The three skeletons fit the connectivity of hypothetical Zintl polyanions of composition [Ψ-S4P2]10-, [Ψ-S2P4]8- and [Ψ-P6]6− respectively. [ABSTRACT FROM AUTHOR]

A topological analysis of the electron localization function (ELF) of a molecule of hexamethyldisiloxane, (H3C)3-Si-O-Si-(CH3)3, has been carried out, drawing a consistent picture of Si-O-Si bonding both in the linear and angular geometries. The ELF analysis confirms the idea that the O atom, in the linear geometry of (H3C)3-Si-O-Si-(CH3)3, is isolobal with the isoelectronic -CH- and -BH3- groups, the bonding in the Si-O-Si group being described as a two-electron, three-center (2 e, 3 c) bond. At the same time, the three oxygen lone pairs mirror the three C-H and B-H bonds, respectively. On the contrary, in the angular geometry the same O atoms form two Si-O bonds and its lone pairs mimic the geometry of the -CH2- group. In this model the O atoms would play the same role as the formally present O2− anions in the `so-called' ionic solids, such as in the skeletons of aluminate and silicate polyanions, thereby connecting molecular and solid-state chemistry as formulated by the `fragment formalism' or the `molecular unit-cell approach'. This unifying concept as well as the calculations we have carried out fully agree and also give support to earlier ideas developed by Bragg and Bent, among other authors. Bonding in the series of compounds P4, P4O6, P4O10, N4(CH2)6 (hexamethylenetetramine) and (CH)4(CH2)6 (adamantane) is discussed in the context of the isolobal model. [ABSTRACT FROM AUTHOR]