Inorganic Chemistry Laboratory at Kanazawa University

Inorganic Chemistry

金沢大学　無機化学研究室

• Condensation Reaction of Oxoacids

The oxoacids of molybdenum, tungsten and vanadium grow from a mononuclear species into a nano-molecule by acid condensation and water elimination reactions, and it results in the formation of polyoxometallates. The precise stoichiometric adjustments with a controlled amount of water and acids, drive the reaction to proceed to make a solution species favourable for a particular anionic framework. The first step is a protonation on a terminal oxido group to give OH species. The OH group has a crucial role in the condensation steps, because it initiates an attack on a metal center resulting to form a dinuclear complex through OH bridging. The reaction is completed by proton transfer reaction on a terminal OH group, prompting the water elimination reaction to afford O-bridging.

• Stepwise Synthesis of Vanadium Oxide Molecules

　We are developing a synthetic methodology of vanadium oxide molecules by a stepwise growth process similar to organic synthesis. Polyoxovanadates have a molecular structure comparable to vanadium oxides and we try to establish the way to control the vanadium oxygen framework for a particular application.

• Three Types of Nano Structures from Three Types of Building Blocks

The versatile vanadium exhibits a variety of coordination environment such as a tetrahedral 4-coordination, a square pyramidal 5-coordination, a trigonal-bipyramidal 5-coordination and an octahedral 6-coordination mode. Square-pyramidal 5-coordination mode is particularly important only in vanadium chemistry. These coordinating polyhedra share their apexes or edges to construct a nano cluster in a geometrical category of a planer complex, a spherical complex, and a block complex mimicking a close-packed solid state structure.

Tetrahedral 4-coordination mode

An apex sharing of tetrahedral units may construct a crown-ether like all-inorganic macrocyclic structure of polyoxovanadates, and it forms inorganic rings acting as an inorganic ligand. The resulting structure combined with transition elements is planer forms.

Square pyramidal 5-coordination mode

Square pyramidal units are equivalent to the pyramid shape, and form fullerene like spherical structures. Inside the cavity, an anionic guest is incorporated because all the bottom of the pyramids where positive vanadium atoms are sitting, is pointing inside the sphere. This is why anionic framework may hold anionic template in the cavity.

Octahedral 6-coordination mode

Assembling octahedral 6-coordination VO6 by edge sharings, produces a molecular oxide that has a structure similar to the NaCl close-packing style in a molecular form.

• Stepwise Synthesis of Inorganic Spheres with a Guest Inside

The removal of the metal cation template from the disk center, followed by the complexation under the presence of an anionic template, the bowl type complex holding the anionic template at the cavity is formed. Here, the metal cation template is replaced by the anion template: the "Umpolung" is happening. The construction of a spherical molecule with a favorite guest inside, is possible after the capping process of a further condensation reaction by a Lewis acid. Disk to bowl to ball reactions. 　

• Playing Molecular Catch

　A bowl-type vanadium-molecule catches a chloride and changes the shape, squeezing it tightly to secure, just like a move of a mitt in baseball game. The resulting complex encloses the chloride and it comes to be no longer reactive with a reagent in solution such as a silver cation. Thanks to the flexibility of an ionic bond, which allows a smooth transformation to reshape a completely different structure. The bond angles in ionic complexes are free to move, not limited by the rigid Td or triangle angles from sp2 or sp3 configuration in organic chemistry. A trigger for the reversible structural changes is the elimination or addition of a proton. It can transform back to the original shape and releasing a ball is possible because of the reversiblity of the isomerism.