title: Synthesis, structure, and bonding of the nonclassical Zintl phase K5As3Pb3.
abstract: The title phase was synthesized by direct fusion of a stoichiometric amount of the elements followed by annealing at 650 degrees C for 3 weeks. The compound crystallizes in the orthorhombic space group Pnma (No. 62), Z = 4, with a = 19.451(6) A, b = 12.164(3) A, c = 6.581(1) A. The compound is made up of As(3)Pb(3)(5-) crown clusters that can be likened geometrically and electronically to 6-atom hypho-clusters derived from a tricapped trigonal prismatic closo parent. These crowns are interconnected via intercluster Pb-Pb bonds to form infinite chains along the b axis, which means the compound contains an extra two cations and two electrons per formula unit. Extended Hückel calculations indicate that the two additional electrons per cluster are accommodated in pi states on the cluster and predict that the phase should be semiconducting. The latter is confirmed by microwave resistivity measurements, rho(298) = 1.0 x 10(2) microOmega.cm; (deltarho/deltaT)/rho = -0.14(3) K(-)(1).
authors.affiliation: Department of Chemistry and Ames Laboratory-DOE, Iowa State University, Ames, Iowa 50011.
authors.forename: Michael T
authors.initials: MT
authors.lastname: Klem
authors.forename: John D
authors.initials: JD
authors.lastname: Corbett
mesh_terms: D001152:Arsenicals / Q000138:chemical synthesis / Q000737:chemistry; D018360:Crystallography, X-Ray; D007854:Lead / Q000737:chemistry; D008956:Models, Chemical; D011188:Potassium / Q000737:chemistry
chemical_list: D001152:Arsenicals; D007854:Lead; D011188:Potassium