| Studies have shown that complex Zintl phases exhibit a rich diversity of crystal structures. These studies have also shown the remarkable success of the Zintl concept in rationalizing crystal structure, stoichiometry, and chemical bonding of many main group intermetallics. However, there are still unresolved questions about the usefulness of the concept in explaining the structure-property relationships of intermetallics along the Zintl border. Limitations of the Zintl concept are represented by violations often associated with “electron-deficient” phases that contain Group 13 post-transition metals. Recent investigations on “electron-deficient” Zintl phases have led to the synthesis of a number of novel inorganic intermetallic π-systems. Since unique structures and properties are already apparent in normal Zintl phases, it is anticipated that exploratory synthesis and characterization of conjugated and multiple-bonded inorganic intermetallic systems will produce not only unusual crystal chemistry but interesting physical properties as well. Reported here are syntheses, crystal and electronic structures, and physical properties of a number of new intermetallic systems. This includes new complex Zintl phases such as: a diamagnetic compound SrCa2In 2Ge—which features [In2Ge]6chains representing a novel inorganic conjugated π-system analogous to a polyallyl chain with In-In double bonds, Ca5In9Sn6—which contains indium trimers, [In3]5– analogous and isoelectronic with the aromatic cyclopropenium cation, [C3H 3]+, Ba5Mg18Ge13—which could be formulated as [5Ba]10+[18Mg]36+[9Ge] 36–[Ge4]10– and features a [Ge4]10– star, isostructural and isoelectronic with PCl 3, the relationship between Zintl phases SrCaGa4(AlB 2-type), CaGaIn(CaIn2-like type), BaIn(CeCu2-type), and CaMgGe(Co2Si-type)—which was discussed in terms of radii ratio of cation and anion sizes, the relationship between CaGaGe, SrInSn, SrGaSn, CaGe1.8Sn0.2, and SrGeSn—which was rationalized by the Zintl concept. Other new Zintl phases, such as Ca2LiInGe 2, featuring puckered layers of 2∞[InGe 4/2]5– built up from all corner-shared tetrahedra like silicates and alluminosilicates, and Sm3Ga2Sn 3 featuring a linked chain of Ga2Sn3 square pyramid, reflect the structural diversity of Zintl phases. The syntheses of these novel intermetallics, Zintl π-systems, and structural studies on complex Zintl phases seek to provide an improved understanding of the chemistry and bonding of intermetallics in the region between metals and nonmetals. |
