Polycation-Polyanion Architecture of the Intermetallic Compound MgGaIr.

MgGaIr ( = 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 6/, Pearson symbol 90, = 18, = 14.4970(3) Å, = 8.8638(3) Å. The composition and atomic arrangement in MgGaIr do not follow the 8- 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. MgGaIr 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- compounds to electron-deficient materials with multi-atomic bonding.