Thermal expansion matching via framework flexibility in zinc dicyanometallates

The thermal expansion properties of two isostructural zinc dicyanometallates that crystallize with and without the inclusion of a weakly interacting secondary crystalline phase have been investigated using variable temperature single-crystal and powder X-ray diffraction. The guest-free Zn[Au(CN)(2)](2) framework was found to show very strong anisotropic positive and negative thermal expansion. In contrast, its cocrystal analogue Zn[Ag(CN)(2)](2) x xAgCN exhibited much more moderate behavior, such that the coefficient of thermal expansion for the host Zn[M(CN)(2)](2) framework now matched that of crystalline AgCN. It was proposed that this correlation points to a more general ability of highly flexible framework materials to "match" the thermal expansivity of adhered phases (e.g., substrates, sorbates, or cocrystallized species), suggesting a methodology of eliminating thermal strain in multicomponent assemblies.