Ba4Si3Br2: a double salt of barium bromide and barium silicide containing a novel cyclotrisilicide unit.

A new compound of the composition Ba4Si3Br2 was obtained by reacting BaSi with a melt of BaBr2. Ba4Si3Br2 may be described as a double salt between a Zintl phase and a halide. The structure was determined by single-crystal X-ray diffraction (P21c, a= 1504.1(2), b = 884.5(1), c = 880.2(1) pm, beta = 101.93(2) degrees, R = 0.041 Rw = 0.079). The crystal structure contains isolated barium cations and bromide anions as well as novel singly bonded cyclotrisilicid units. The electronic structure has been studied by linear Muffin tin orbital (LMTO) band structure calculations, which reveal semiconducting behavior with a band gap of about 0.1 eV, and by an analysis of the electron localization function.