NA3HG - THE MOST SODIUM RICH AMALGAM IN THE SYSTEM SODIUM-MERCURY

Na3Hg is the most sodium rich amalgam in the system sodium-mercury. It crystallizes in two different modifications: alpha-Na3Hg (hexagonal, a = 5.433(1) angstrom, c = 9.795(2) angstrom, modified Na3As-type) and beta-Na3Hg (pseudocubic, a = 7.63 angstrom, modified Li3Bi-type). Both crystal structures are (in a strongly idealized description) characterized by "wide spaced" close packings of mercury atoms (d(Hg-Hg) > 5 angstrom) with all tetrahedral and octahedral holes filled by sodium atoms. Microcrystalline samples of both compounds are prepared and characterized by X-ray crystallography. A weak but significant deviation of the betA-Na3Hg structure from the cubic symmetry is obvious. In addition single crystals of alpha-Na3Hg are investigated at room temperature. The thermal displacement ellipsoides of the sodium atoms in alpha-Na3Hg give strong evidence for characteristic deviations from the ideal Na3As structure.