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‐NO 2 )(pyz)] ( 1 , 2 ) are composed of dimerised ( 1 ) and delaminated ( 2 ) AgNO 2 /pyrazine, which convert to the ground‐state [Ag(κ 2 ‐NO 2 )(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.