Stereoisograms of trigonal bipyramidal compounds: I. Chirality and RS-stereogenicity free from the conventional “chirality” and “stereogenicity”

Abstract

The stereoisogram approach, which has originally been developed to rationalize organic stereochemistry (Fujita in J Org Chem 69:3158–3165, 2004; Fujita in Tetrahedron 62:691–705, 2006; 65:1581–1592, 2009), is extended and applied to inorganic stereochemistry by using trigonal bipyramidal compounds as examples. The point group D3h of a trigonal bipyramidal skeleton is extended into the RS-stereoisomeric group of order 24, which is considered to control a stereoisogram of the trigonal bipyramidal skeleton. Stereoisograms of trigonal bipyramidal compounds derived from the skeleton correspond to subgroups of the RS-stereoisomeric group. Thereby, they are discussed in terms of attributive terms (chirality/achirality, RS-stereogenicity/RS-astereogenicity, and sclerality/asclerality) or equivalently in terms of relational terms (enantiomeric/self-enantiomeric, RS-diastereomeric/self-RS-diastereomeric, and holantimeric/self-holantimeric), where the stereoisograms are categorized into five types (Types I–V). Among them, stereoisograms of Types I, III, and V are shown to be capable of giving C/A-descriptors because of their RS-stereogenicity (or RS-diastereomeric relationships).