Polycation–Polyanion Architecture of the Intermetallic Compound Mg3−xGa1+xIr

Abstract

Mg3−xGa1+xIr (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 P63/mcm, Pearson symbol hP90, Z = 18, a = 14.4970(3) Å, c = 8.8638(3) Å. 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.

Be3Ru: Polar Multiatomic Bonding in the Closest Packing of Atoms

“…[29] The shape of the QTAIM Ru species in Be 3 Ru reveals some characteristic features (Figure 4 , top). It is far from a spherical one and has concave surfaces toward neighboring beryllium species, similar to the platinum and beryllium atoms in Be 21 Pt 5 [3] or iridium and magnesium atoms in Mg 3 Ga 1‐x Ir 3+x , [7] where this feature is correlated with the strong charge transfer. The beryllium species look like ‘soft tetrahedrons’ resembling atomic shapes of Be and Mg in the two above‐mentioned compounds.…”

“…These DOS features, in combination with a low electron number in the last shell per atom (ELSA [7,28] ) raise questions about their origin from the point of view of chemical bonding interaction.…”

“…The analysis of chemical bonding was performed by quantum chemical techniques in position space, which has recently been shown to be a powerful bonding investigation tool, in particular for intermetallic compounds with low ELSA and multi‐atomic bonding. [ 3 , 4 , 7 ] The effective charges of all atoms were determined from the calculated electron density. First, the zero‐flux surfaces in the gradient vector field of the electron density were determined.…”

“…A combination of elements from the group 13 with those from the group 15 or between elements from group 12 with those from group 16, can give rise to semiconducting materials – for example GaAs [5] or ZnSe, [6] which are characterized by two‐center‐two‐electron moderately polar bonds. Moving to the left side of the Periodic Table, where the number of electrons in the last shell (ELSA [7] ) is reduced, different bonding scenarios can be observed, depending on the difference in electronegativity between the components. When the difference in electronegativity is very large, Zintl phases are the protagonists: the cationic part donates its valence electrons to the anionic one to form two center‐ and/or multiatomic bonds with moderate polarity in the anion sublattices.…”

Mg29–xPt4+y: Chemical Bonding Inhomogeneity and Structural Complexity

“…The so-obtained shapes are similar to those described for the chemically homologous compounds Be 21 Pt 5 , 20 Be 5 Pt, 21 and Mg 3 GaIr. 30 The Mg atoms reveal compact convex polyhedra, and Pt shows large units with concave faces. Integration of the ED within these atomic basins yields their electronic population; subtracting the atomic number from the latter results in the effective charge.…”