Synthesis and Structure of K3Mg20In14, a Stuffed Variant of the BaHg11 Structure Type with a Magnesium−Indium Network

The phase K3Mg20In14 was synthesized via high-temperature reactions of the elements in welded Ta tubes. The cubic crystal structure established by single-crystal X-ray diffraction means [space group Pm3m, Z = 1, a = 9.769(1) angstroms] features a 3D Mg-In network formed by K@Mg12In10 units plus cuboctahedral fillers, In@Mg12. This is the first example of a well-ordered stuffed BaHg11 structure (Pearson symbol cP37). On the basis of tight-binding linear muffin-tin orbital, atomic sphere approximation calculations, the electronic structure of the compound shows dominant Mg-In interactions and substantial participation of Mg in the overall network bonding. Both In-In and Mg-In bondings are effectively optimized at the Fermi level. The Fermi energy cuts through substantial densities of states, consistent with the measured metallic property.

Nonclassical Bonding in the Novel Structure of Ba2Bi3 and Unexpected Site Preference in the Coloring Variant Ba2BiSb2

The new phase Ba(2)Bi(3) crystallizes in the W(2)CoB(2) structure type. Its structure contains rigorously planar anionic layers of (4.6.4.6)(4.6(2))(2) nets with three- and four-bonded Bi, that are separated by Ba atoms. An unexpected site preference is observed in the coloring variant Ba(2)BiSb(2) with Sb occupying only the three-bonded sites. The nonclassical bonding in the anionic network can be rationalized from a reformulation of the Zintl concept as (Ba(2+))(2)[Bi(3)](3)(-)(e(-)). Bonding distances suggest that the extra electron fills Bi-Bi antibonding states. The densities of states obtained from TB-LMTO-ASA calculations show metallic character for both compounds.