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In chemistry the polyhedral skeletal electron pair theory provides electron counting rules useful for predicting the structures of clusters such as borane and carborane clusters. The electron counting rules were originally formulated by Kenneth Wade〔''The structural significance of the number of skeletal bonding electron-pairs in carboranes, the higher boranes and borane anions, and various transition-metal carbonyl cluster compounds'' K. Wade J. Chem. Soc. D, 1971, 792-793 〕 and were further developed by D. M. P. Mingos〔''A General Theory for Cluster and Ring Compounds of the Main Group and Transition Elements'' D. M. P. MINGOS Nature Physical Science 236, 99-102 〕 and others; they are sometimes known as Wade's rules or the Wade/Mingos rules.〔''The significance and impact of Wade's rules'' Alan J. Welch Chem. Commun., 2013,49, 3615-3616 〕 The rules are based on a molecular orbital treatment of the bonding.〔 These notes contained original material that served as the basis of the sections on the 4n, 5n, and 6n rules.〕 These rules have been extended and unified in the form of the Jemmis mno rules. ==Predicting structures of cluster compounds== Different rules (4n, 5n, or 6n) are invoked depending on the number of electrons per vertex. The 4n rules are reasonably accurate in predicting the structures of clusters having about 4 electrons per vertex, as is the case for many boranes and carboranes. For such clusters, the structures are based on deltahedra, which are polyhedra in which every face is triangular. The 4n clusters are classified as ''closo-, nido-, arachno- or hypho-,'' based on whether they represent a complete (''closo-'') deltahedron, or a deltahedron that is missing one (''nido-''), two (''arachno-'') or three (''hypho-'') vertices. However, hypho clusters are relatively uncommon due to the fact that the electron count is high enough to start to fill antibonding orbitals and destabilize the 4n structure. If the electron count is close to 5 electrons per vertex, the structure often changes to one governed by the 5n rules, which are based on 3-connected polyhedra. As the electron count increases further, the structures of clusters with 5n electron counts become unstable, so the 6n rules can be implemented. The 6n clusters have structures that are based on rings. A molecular orbital treatment can be used to rationalize the bonding of cluster compounds of the 4n, 5n, and 6n types. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Polyhedral skeletal electron pair theory」の詳細全文を読む スポンサード リンク
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