The Nature of the Chemical Bond in Linear Three-Body Systems: FromI3–to Mixed Chalcogen/Halogen and Trichalcogen Moieties

[摘要] The 3 centre-4 electrons (3c-4e) and the donor/acceptor or charge-transfer models for the description of the chemical bond in linear three-body systems, such asI3−and related electron-rich (22 shell electrons) systems, are comparatively discussed on thegrounds of structural data from a search of the Cambridge Structural Database (CSD). Both modelsaccount for a total bond order of 1 in these systems, and while the former fits better symmetric systems,the latter describes better strongly asymmetric situations. The 3c-4e MO scheme shows that anylinear system formed by three aligned closed-shell species (24 shell electrons overall) has reason toexist provided that two electrons are removed from it to afford a 22 shellelectrons three-body system: all combinations of three closed-shell halides and/or chalcogenides areconsidered here. A survey of the literature shows that most of these three-body systems exist. Withsome exceptions, their structural features vary continuously from the symmetric situation showing twoequal bonds to very asymmetric situations in which one bond approaches to the valuecorresponding to a single bond and the second one to the sum of the van der Waals radii of theinvolved atoms. This indicates that the potential energy surface of these three-bodysystems is fairly flat, and that the chemical surrounding of the chalcogen/halogen atoms can play animportant role in freezing different structural situations; this is well documented for theI3−anion. The existence of correlations between the two bond distances and more importantlythe linearity observed for all these systems, independently on the degree of their asymmetry, support thestate of hypervalency of the central atom.

[学科分类] 物理化学和理论化学