Ba11Cd8Bi14:: Bismuth zigzag chains in a ternary alkaline-earth transition-metal Zintl phase

A new transition-metal-containing Zintl phase, Ba11Cd8Bi14, has been synthesized by a Cd-flux reaction, and its structure has been determined by a single-crystal X-ray diffraction. Ba11Cd8Bi14 crystallizes in the monoclinic space group C2/m (No. 12, Z = 2) with a = 28.193(8) A, b = 4.8932(14) A, c = 16.823(5) A, and beta = 90.836(4)degrees, taken at -150 degrees C (R1 = 0.0407, wR2 = 0.1016). The structure can be described as being built of complex polyanionic [Cd8Bi14](22-) layers running along the b axis, which are separated by the Ba2+ cations. An interesting feature of these layers is that they are composed of novel centrosymmetric chains of corner- and edge-shared CdBi4 tetrahedra, interconnected through exo-Bi-Bi bonds. These bonds connect terminal Bi atoms from adjacent chains in such a way that infinite zigzag chains of bismuth parallel to the same direction are formed. Electronic band structure calculations performed using the TB-LMTO-ASA method show a very small band gap, suggesting a narrow-gap semiconducting or poor metallic behavior for Ba11Cd8Bi14. The crystal orbital Hamilton population (COHP) analysis on the homo- and heteroatomic interactions in this structure is reported as well.