Polycyano–polycadmate host clathrates including a methylviologen dication. Syntheses, crystal structures and photo-induced reduction of methylviologen dication

Abstract

A series of polycyano–polycadmate host clathrates including a methylviologen dication (MV²⁺), which is a strong electron acceptor, and an organic molecule, such as alcohols, haloalkanes, ethers and small aromatics, and two complexes built of a polycyano–polycadmate and MV²⁺ have been synthesized. Single crystal X-ray diffraction experiments on ten clathrates and the two complexes revealed their 3-D network polycyano–polycadmate structures constructed with Cd²⁺ ions and CN⁻ bridges. The network structures are classified into five structure types. Type I, II and III were found in the clathrates, and Type IV and V were found in the two complexes. Type I and II have cage-like cavities and each of the cavities includes one guest, MV²⁺ or an organic molecule. Type III has a channel-like cavity where MV²⁺ ions and organic molecules are included. Type IV and V have 3-D cavities, the shape of which is neither cage-like nor channel-like, for embracing MV²⁺. Although all compounds were colorless and the formation of a charge transfer complex between MV²⁺ and a neutral guest in the clathrates was not confirmed from the crystal structure data and diffuse reflectance spectra, some of them showed a color change from colorless to blue on UV irradiation, which arose from the reduction of MV²⁺ to a methylviologen radical cation MV⁺˙.