Past, present and future of the clathrate inclusion compounds built of cyanometallate hosts

One-, two- and three-dimensional CN-bridged metal complex structures made up of building blocks such as linear [Ag(CN)(2)](-), square planar [Ni(CN)(4)](2-) or tetrahedral [Cd(CN)(4)](2-), and of the complementary ligands such as ammonia, water, unidentate amine, bidentate alpha,omega-diaminoalkane, etc., are reviewed with an emphasis on their behaviour as hosts to afford clathrate inclusion compounds with guest molecules and as self-assemblies to form supramolecular structures with or without guests. The historical background is explained for Prussian blue and Hofmann's benzene clathrate based on their single crystal structure determinations. The strategies the author and coworkers have been applying to develop varieties of clathrate inclusion compounds from the Hofmann-type are demonstrated with the features observed for the developed structures determined by single crystal X-ray diffraction methods.