Zintl cluster chemistry in the alkali-metal-gallium systems

摘要

Previous research into the alkali-metal-gallium systems has revealed a large variety of networked gallium deltahedra. The clusters are analogues to borane clusters and follow the same electronic requirements of 2n+2 skeletal electrons for closo-deltahedra. This work has focused on compounds that do not follow the typical electron counting rules. The first isolated gallium cluster was found in Cs(sub 8)Ga(sub 11). The geometry of the Ga(sub 11)(sup 7(minus)) unit is not deltahedral but can be described as a penta-capped trigonal prism. The reduction of the charge from a closo-Ga(sub 11)(sup 13(minus)) to Ga(sub 11) (sup 7(minus)) is believed to be the driving force of the distortion. The compound is paramagnetic because of an extra electron but incorporation of a halide atom into the structure captures the unpaired electron and forms a diamagnetic compound. A second isolated cluster has been found in Na(sub 10) Ga(sub 10)Ni where the tetra-capped trigonal prismatic gallium is centered by nickel. Stabilization of the cluster occurs through Ni-Ga bonding. A simple two- dimensional network occurs in the binary K(sub 2)Ga(sub 3) Octahedra are connected through four waist atoms to form a layered structure with the potassium atoms sitting between the layers. Na(sub 30.5)Ga(sub 60(minus)x) Ag(sub x) is nonstoichiometric and needs only a small amount of silver to form (x (approximately) 2--6). The structure is composed of three different clusters which are interconnected to form a three-dimensional structure. The RbGa(sub 3(minus)x)Au(sub x) system is also nonstoichiometric with a three-dimensional structure composed of Ga(sub 8) dodecahedra and four-bonded gallium atoms. Unlike Na(sub 30.5)Ga(sub 60(minus)x)Ag(sub x), the RbGa(sub 3) binary is also stable. The binary is formally a Zintl phase but the ternary is not. Some chemistry in the alkali-metal-indium system also has been explored. A new potassium-indium binary is discussed but the structure has not been completely characterized.