BONDING PROPERTIES OF CA14GAAS11 - A COMPOUND CONTAINING DISCRETE GAAS4 TETRAHEDRA AND A HYPERVALENT AS3 POLYATOMIC UNIT

We have theoretically studied the bonding properties of Ca14GaAs11 using the ab initio, self-consistent pseudopotential method within the local density approximation of density functional theory. Ca14GaAs11 is an example of a new series of recently prepared compounds which have the stoichiometry A14MPn11 (A = Ca, Sr, Ba; M = Al, Ga, Mn; Pn = As, Sb, Bi). We have found that the electronic structure and bonding of the Ca14GaAs11 compound are consistent with the Zintl concept. In addition, the GaAs4 tetrahedra and the linear As3 groups contained in this compound are isolated units which are not arranged into an extended bonding network. The bonding within the GaAs4 group is slightly more ionic than the bonding in a GaAs crystal. The linear As3 unit can be accurately described as a hypervalent three-center, four-electron bonded structure. The A14MPn11 structure type contains the first example of a discrete, hypervalent group 15 linear anion.