Polycation-Polyanion Architecture of the Intermetallic Compound Mg 3- x Ga 1+ x Ir.

Mg 3- x Ga 1+ x Ir ( x = 0.05) was synthesized by direct reaction of the elements in welded tantalum containers at 1200 °C and subsequent annealing at 500 °C for 30 days. Its crystal structure represents a new prototype and was determined by single-crystal technique as follows: space group P 6 3 / mcm , Pearson symbol hP 90, Z = 18, a = 14.4970(3) Å, c = 8.8638(3) Å. The composition and atomic arrangement in Mg 3 GaIr do not follow the 8- N rule due to the lack of valence electrons. Based on chemical bonding analysis in positional space, it was shown that the title compound has a polycationic-polyanionic organization. In comparison with other known intermetallic substances with this kind of bonding pattern, both the polyanion and the polyanion are remarkably complex. Mg 3- x Ga 1+ x Ir is an example of how the general organization of intermetallic substances (e.g., formation of polyanions and polycations) can be understood by extending the principles of 8- N compounds to electron-deficient materials with multi-atomic bonding.