Natural resonance-theoretic conceptions of extreme electronic delocalization in soft materials

In the broad context of Dalton's atomic hypothesis and subsequent classical vs. quantum understanding of macroscopic materials, we show how Pauling's resonance-type conceptions, as quantified in natural resonance theory (NRT) analysis of modern wavefunctions, can be modified to unify description of interatomic interactions from the Lewis-like limit of localized e-pair covalency in molecules to the extreme delocalized limit of supramolecular “soft matter” aggregation. Such “NRT-centric” integration of NRT bond orders for hard- and soft-matter interactions is illustrated with application to a long-predicted and recently synthesized organometallic sandwich-type complex (“diberyllocene”) that exhibits bond orders ranging from the soft limit (b_BeC ≈ 0.01) to the typical values (b_CC ≈ 1.35) of molecular resonance-covalency in the organic domain, with intermediate value (b_BeBe ≈ 0.86) for intermetallic Be⋯Be interaction.