Overlooked Binary Compounds Uncovered in the Reinspection of the La–Au System: Synthesis, Crystal Structures, and Electronic Properties of La(7)Au(3), La(3)Au(2), and La(3)Au(4)

[Image: see text] Although compound formation between two elements is well studied, thorough investigations make it possible to uncover new binary compounds. A re-examination of the La–Au system revealed three new phases, which were characterized with respect to their structural and electronic properties as well as thermal stability: La(7)Au(3) (Th(7)Fe(3) type, space group P6(3)mc, Pearson code hP20) appears to be metastable. It can be obtained by slow crystallization from a stoichiometric melt. La(3)Au(2) (U(3)Si(2) type, space group P4/mbm, Pearson code tP10) is stable up to 1013 K, where it decomposes peritectically. La(3)Au(4) (Pu(3)Pd(4) type, space group R3̅, Pearson code hR14) is thermally stable up to at least 1273 K. In addition, the crystal structures of La(2)Au (anti-PbCl(2) type, space group Pnma, Pearson code oP12) and α-LaAu (FeB type, space group Pnma, Pearson code oP8) could be determined by single-crystal X-ray diffraction. The electronic structures and chemical bonding have been evaluated from first principles calculations. They show that all compounds can be viewed as electron-rich, polar intermetallics.