Anion···π Interactions and Metastability: Structural Transformations in a Silver–Pyrazine Network

Structural evidence of anion···π interactions influencing single-crystal-to-single-crystal (SCSC) transformations is demonstrated herein with a metastable silver–pyrazine system. A cascade of SCSC transformations driven by changes to anion···π stabilisation sees two metastable species convert to a ground-state form. This constitutes one of the most dramatic chemical effects yet attributed to anion···π interactions. Metastable networks [Ag(µ-NO₂)(pyz)] (1, 2) are composed of dimerised (1) and delaminated (2) AgNO₂/pyrazine, which convert to the ground-state [Ag(κ²-NO₂)(pyz)] form 3 with 3D connectivity. The metastable phases show responsiveness to solvent vapour and temperature. This work shows how anion···π interactions influence solid-state structure with support from computational modelling and highlights how metastable materials may harness anion···π interactions to deliver large structural and property changes.