Layered rare-earth gallium antimonides REGaSb(2) (RE = La--Nd, Sm)

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.

Planar Nets of Ti Atoms Comprising Squares and Rhombs in the New Binary Antimonide Ti2Sb

The new binary antimonide Ti(2)Sb was found to crystallize in a distorted variant of the La(2)Sb type, which contains a square planar La net with short La-La bonds. In the Ti(2)Sb structure, the corresponding Ti net is deformed to squares and rhombs in order to enhance Ti-Ti bonding, as proven by single-crystal X-ray investigation in combination with the real-space pair distribution function technique utilizing both X-ray and neutron powder diffraction data. Electronic structure calculations revealed a lowering of the total energy caused by the disorder, the major driving force being strengthened Ti-Ti interactions along the diagonal of the Ti(4) rhombs.

Lanthanum gallium bismuthide, LaGaBi2

The ternary rare-earth gallium bismuthide LaGaBi(2) has been prepared through reaction of the elements. Its structure (Pearson symbol hP24, hexagonal, space group P6/mmm, Z = 6, a = 13.5483(4) A, c = 4.3937(1) A) contains columns of La(6) trigonal prisms centered by Bi atoms. These columns are surrounded by a framework consisting of three-atom-wide Bi ribbons and Ga(6) rings. Additional Bi atoms are sandwiched between pairs of Ga(6) rings. LaGaBi(2) is structurally closely related to La(13)Ga(8)Sb(21). A retrotheoretical analysis of the structure through extended Hückel band structure calculations suggests an interesting electronic situation in which strong multiple bonding in the Ga-Ga network coexists with weak hypervalent bonding in the Bi-Bi network and confirms the metallic behavior seen in electrical resistivity measurements.