Tridymite-like host clathrate [K(H2O)n][CuZn(CN)4]: crystal structure, guest molecular motion and properties

Abstract

A new clathrate [K(H₂O)_n][CuZn(CN)₄] has been synthesized and its host structure has been determined by the single-crystal X-ray diffraction method. It has a [CuZn(CN)₄]⁻tridymite-like 3D framework host, formed with tetrahedral Cu(I) and Zn(II) ions and cyanide bridges and includes water molecules as guests, together with K⁺. This tridymite-like structure is the first structural variation of the [CuZn(CN)₄]⁻ 3D framework, whose only known structure has been a cristobalite-like structure. The new host shows properties never seen in the previous cristobalite-like structure host. It absorbs and desorbs water as a guest and the water content (n) varies between 1.2 and 11.2 at room temperature, by adjusting the conditions where the clathrate is placed. The desorption of the water causes deformation of the host structure and this deformation is recovered by the absorption of water. The water can be replaced with methanol and acetonitrile by their absorption instead of water. Solid-state ²H-NMR spectra revealed the molecular motion of the water, methanol and acetonitrile guests in a temperature range between 123 K and 300 K.