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Ba and Sr Binary Phosphides: Synthesis, Crystal Structures, and Bonding Analysis

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posted on 08.09.2015 by Juli-Anna Dolyniuk, Hua He, Alexander S. Ivanov, Alexander I. Boldyrev, Svilen Bobev, Kirill Kovnir
Synthesis, crystal structures, and chemical bonding are reported for four binary phosphides with different degrees of phosphorus oligomerization, ranging from isolated P atoms to infinite phosphorus chains. Ba3P2 = Ba4P2.670.33 (□ = vacancy) crystallizes in the anti-Th3P4 structure type with the cubic space group I4̅3d (no. 220), Z = 6, a = 9.7520(7) Å. In the Ba3P2 crystal structure, isolated P3– anions form distorted octahedra around the Ba2+ cations. β-Ba5P4 crystallizes in the Eu5As4 structure type with the orthorhombic space group Cmce (no. 64), Z = 4, a = 16.521(2) Å, b = 8.3422(9) Å, c = 8.4216(9) Å. In the crystal structure of β-Ba5P4, one-half of the phosphorus atoms are condensed into P24– dumbbells. SrP2 and BaP2 are isostructural and crystallize in the monoclinic space group P21/c (no. 14), Z = 6, a = 6.120(2)/6.368(1) Å, b = 11.818(3)/12.133(2) Å, c = 7.441(2)/7.687(2) Å, β = 126.681(4)/126.766(2)° for SrP2/BaP2. In the crystal structures of SrP2 and BaP2, all phosphorus atoms are condensed into 1P1– cis–trans helical chains. Electronic structure calculations, chemical bonding analysis via the recently developed solid-state adaptive natural density partitioning (SSAdNDP) method, and UV–vis spectroscopy reveal that SrP2 and BaP2 are electron-balanced semiconductors.