Anion···? interactions and metastability: structural transformations in a silver-pyrazine network

Structural evidence of anion···? 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···? stabilisation sees two metastable species convert to a ground-state form. This constitutes one of the most dramatic chemical effects yet attributed to anion···? interactions. The metastable networks, [Ag(?-NO2)(pyz)] (1-2), are composed of dimerised (1) and delaminated (2) AgNO2/pyrazine, which convert to the ground-state [Ag(?2-NO2)(pyz)] form (3) with 3D connectivity. The metastable phases show responsiveness to solvent vapour and temperature. This work shows how anion···? interactions influence solid-state structure with support from computational modelling, and highlights how metastable materials may harness anion···? interactions to deliver large structural and property changes.