Helices, chirality and interpenetration: The versatility and remarkable interconversion of silver-copper cyanide frameworks

Abstract

The structural transformations between cesium silver-copper cyanides under modest conditions, both in solution and in the solid state, are described. Three new cesium silver(I) copper(I) cyanides with three-dimensional (3-D) framework structures were prepared as single crystals from a one-pot reaction initially heated under hydrothermal conditions. The first product to appear, Cs 3Ag2Cu3(CN)8 (I), when left in contact with the supernatant produced CsAgCu(CN)3 (II) and CsAgCu(CN)3·1/3H2O (III) over a few months via a series of thermodynamically controlled cascade reactions. Crystals of the hydrate (III) can be dehydrated to polycrystalline CsAgCu(CN)3 (II) on heating at 100°C in a remarkable solid-state transformation involving substantial breaking and reconnection of metal-cyanide linkages. Astonishingly, the conversion between the two known polymorphs of CsAg2Cu(CN) 4, which also involves a major change in connectivity and topology, occurs at 180°C as a single-crystal to single-crystal transformation. Structural features of note in these materials include the presence of helical copper-cyanide chains in (I) and (II), which in the latter compound produce a chiral material. In (II) and (III), the silver-copper cyanide networks are both self- and interpenetrating, features also seen in the known polymorphs of CsAg2Cu(CN)4. © 2009 American Chemical Society.