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Abstract:
Mg3-xGa1+xIr (x = 0.05) was synthesized by direct reaction of the elements in welded tantalum containers at 1200 degrees C and subsequent annealing at 500 degrees C for 30 days. Its crystal structure represents a new prototype and was determined by single-crystal technique as follows: space group P6(3)/mcm, Pearson symbol hP90, Z = 18, a = 14.4970(3) angstrom, c = 8.8638(3) angstrom. The composition and atomic arrangement in Mg3GaIr 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. Mg3-xGa1+xIr 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.
