Helices, Chirality and Interpenetration: the Versatility and Remarkable Interconversion of Silver-Copper Cyanide Frameworks

摘要

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_3Ag_2Cu_3(CN)_8 Ⅰ, when left in contact with the supernatant produced CsAgCu(CN)_3 (Ⅱ) and CsAgCu(CN)_3·1/3H_2O 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 ℃ in a remarkable solid-state transformation involving substantial breaking and reconnection of metal-cyanide linkages. Astonishingly, the conversion between the two known polymorphs of CsAg_2Cu(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 CsAg_2Cu(CN)_4.