Photofunctional chromic metal complexes that exhibit remarkable luminescence and color changes in response to gentle stimuli such as chemical vapor and mechanical stimulus have been extensively developed. In particular, squareplanar Pt(II) complex systems that exhibit assembly-induced emission based on the Pt···Pt electronic interactions are significant for vapochromic materials with high sensitivity. The crystal engineering using various intermolecular interactions as well as ligand design realized photofunctional chromic complexes with intense luminescence and/or selective chromic behaviors. In addition to Pt(II) complexes, vapoluminescent Cu(I) complexes were also developed using their labile properties. Selective vapor response accompanied by the remarkable color change coupled with spinstate change was found for a Ni(II) complex bearing a quinonoid ligand. Based on these achievements, a new scientific area regarding flexible response systems with high structural order is developing covering various molecular crystalline materials called soft crystals.

The mechanism that controls the self-assembly of complex polyoxometalate inorganic clusters in solution is a challenge because the clusters can contain anywhere from 6 to 368 metal ions in a single molecule and are commonly assembled under ʻone-potʼ reaction conditions. Furthermore, harnessing the ʻself-assemblyʼ processes allows synthesis on a length-scale and with a degree of complexity which is not easily accessed by more traditional ʻstep-wiseʼ synthesis routes. This class of molecules are important as they can be thought of as ʻmolecular metal oxidesʼ and rival the size of proteins yet are based upon simple MO_x units (where M is Mo, W, V and sometimes Nb and x can be 4, 5, 6 or 7). Here we review the structures of the molybdenum-based clusters and then show how it is possible to not only control the architectures but explore the mechanism of formation invoking mechanisms that are normally found in biological systems. We describe how a simple inorganic salt can spontaneously form ʻinformation-richʼ, autocatalytic sets of replicating inorganic molecules that work via molecular recognition based on the [PMo₁₂O₄₀]^3–, {PMo₁₂} Keggin ion, and [Mo₃₆O₁₁₂(H₂O)₁₆]^8–, {Mo₃₆} cluster. These small clusters are involved in an autocatalytic network, where the assembly of gigantic molybdenum blue wheels [Mo₁₅₄O₄₆₂H₁₄(H₂O)₇₀]^14– {Mo₁₅₄}, [Mo₁₃₂O₃₇₂(H₂O)₇₂(CH₃CO₂)₃₀]^42–, {Mo₁₃₂} ball containing 154 and 132 molybdenum clusters are templated by the smaller clusters which are themselves able to catalyze their own formation. Finally, We introduce assembly theory and show how assembly theory can be used to describe the constraints that need to be present to facilitate the assembly of the large clusters and explain how information theoretic arguments might be useful for designing highly functional and unsymmetrical inorganic molecules.

η²-Disilene transition-metal complexes have been synthesized by a wide variety of synthetic methods and characterized by X-ray diffraction studies. Their reactivity has been extensively studied so far. However, coordination chemistry of silanimine and phosphasilene, which possess the silicon–nitrogen and silicon–phosphorus double bonds, respectively, has not been well explored, probably due to their instability derived from the polarized silicon–nitrogen and silicon–phosphorus bonds. This review describes the syntheses, structures, and reactivities of η²-silanimine, η¹-silanimine, η²-phosphasilene, and η¹-phosphasilene complexes, as well as metallosilanimines and metallophosphasilenes. Bonding schemes between transition-metals and silanimine/phosphasilene ligands are mentioned in relation to the Dewar, Chatt, and Duncanson (DCD) model. As related compounds, η²-aminosilyl and η²-phosphinosilyl complexes, which include the three-membered ring composed of transition-metal, silicon, and group 15 elements, are also described. A base-stabilized phosphido(silylene) complex can be postulated as a canonical structure of η²-phosphinosilyl complexes and confirmed by experimental and theoretical studies. η²-Phosphinosilyl complexes would be a good activator of small organic molecules, in which the silicon and phosphorus atoms work cooperatively as a Lewis acid and Lewis base, respectively.