Valence bond structures for molecules with 5-electron 3- centre bonding units

Abstract

It is shown how use of valence bond structures of the type ▪ for a 5-electron 3-centre bonding unit can help to provide compact valence bond representations of the electronic structures for NO2, N2O4, excited O3 and SO2, SO3, SO2Y2 (with Y = OH−, O− or F), ClO2, SO2−, S2O42−, [Cu(H2O)6]2+ and an NHN linkage. Without atomic valence shell expansions, many of these structures provide electronic interpretations for hypervalent 19th century type bond diagrams. As an example, it is shown that the 5-electron 3-centre valence bond structure for N2O4 (which is equivalent to resonance between 144 canonical Lewis structures) provides an electronic interpretation for Frankland’s 1866 bond diagram with pentavalent nitrogen atoms.