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Abstract
Hypervalency in XeF2 and isoelectronic complexes is generally understood in terms of the Rundle–Pimentel model (which invokes a three-centre/four-electron molecular system) or its valence bond version as proposed by Coulson, which replaced the old expanded octet model of Pauling. However, the Rundle–Pimentel model is not always successful in describing such complexes and has been shown to be oversimplified. Here using ab initio valence bond theory coupled to quantum Monte Carlo methods, we show that the Rundle–Pimentel model is insufficient by itself in accounting for the great stability of XeF2, and that charge-shift bonding, wherein the large covalent–ionic interaction energy has the dominant role, is a major stabilizing factor. The energetic contribution of the old expanded octet model is also quantified and shown to be marginal. Generalizing to isoelectronic systems such as ClF3, SF4, PCl5 and others, it is suggested that charge-shift bonding is necessary, in association with the Rundle–Pimentel model, for hypervalent analogues of XeF2 to be strongly bonded. Complexes featuring rare gas atoms can be very strongly bonded even though these hypervalent molecules violate the octet rule. Now ab initio valence bond calculations on the XeF2 prototype highlight the essential role of charge-shift bonding, in which the covalent–ionic resonance energy is exceptionally large. Cite this article
Braïda, B., Hiberty, P. The essential role of charge-shift bonding in hypervalent prototype XeF2. Nature Chem 5, 417–422 (2013). https://doi.org/10.1038/nchem.1619 