The crystal structure of cesium tribromide and a comparison of the Br₃ ⁻ and I₃ ⁻ systems

Abstract

The crystal structure of CsBr3 has been determined by X-ray diffraction techniques. The unit cell is orthorhombic with a=6.52, b=10.04 and c=9"54A. The space group is Pmnb. The tribromide ion is nearly linear, but unsymmetrical, with Br-Br distances of 2.440 and 2.698 A,. The Br7 ions in this compound, in PBr7, and in [(CH3)3NH+]2Br-Br7 form a system analogous to that of 17 in which the configuration of the trihalide ion depends on the cation present in the crystal. A qualitative discussion comparing the two systems is given.

Thermodynamic Stability and Defect Chemistry of Bismuth‐Based Lead‐Free Double Perovskites

“…Furthermore, to avoid the formation of the competing secondary phases including CsBr (cubic phase, space group Fm3 m), CsBr 3 (orthorhombic, Pmnb), [20] AgBr( cubic, Fm3 m), BiBr 3 (monoclinic, P2 1 /a), [21] CsAgBr 2 (tetragonal, P4/nmm), [22] Cs 2 AgBr 3 (orthorhombic, Pnma), [22] and Cs 3 Bi 2 Br 9 (trigonal, P3 m1), [23] the following conditions must also be satisfied: Furthermore, to avoid the formation of the competing secondary phases including CsBr (cubic phase, space group Fm3 m), CsBr 3 (orthorhombic, Pmnb), [20] AgBr( cubic, Fm3 m), BiBr 3 (monoclinic, P2 1 /a), [21] CsAgBr 2 (tetragonal, P4/nmm), [22] Cs 2 AgBr 3 (orthorhombic, Pnma), [22] and Cs 3 Bi 2 Br 9 (trigonal, P3 m1), [23] the following conditions must also be satisfied:…”

“…where DH Cs 2 AgBiBr 6 is the formation enthalpy of Cs 2 AgBiBr 6 as referred to elemental Cs, Ag, Bi, and Br 2 phases.T oe xclude the coexistence of elemental phases, it is required that Dm Cs < 0, Dm Ag < 0, Dm Bi < 0, and Dm Br < 0. Furthermore, to avoid the formation of the competing secondary phases including CsBr (cubic phase, space group Fm3 m), CsBr 3 (orthorhombic, Pmnb), [20] AgBr( cubic, Fm3 m), BiBr 3 (monoclinic, P2 1 /a), [21] CsAgBr 2 (tetragonal, P4/nmm), [22] Cs 2 AgBr 3 (orthorhombic, Pnma), [22] and Cs 3 Bi 2 Br 9 (trigonal, P3 m1), [23] the following conditions must also be satisfied: Under these constrains, Dm Cs , Dm Ag ,a nd Dm Br that stabilize Cs 2 AgBiBr 6 are bound in ap olyhedrona ss hown in Figure 2a, whereas Dm Br is associated with Dm Cs , Dm Ag ,a nd Dm Bi through Equation (2). The polyhedron exhibits al ong but narrow shape, which meanst hat the chemical conditions should be carefullyc ontrolled to obtain single-phase Cs 2 AgBiBr 6 and avoid impurity phases, similart ot he Pb-and Sn-based halide perovskites.…”

Darstellung und Kristallstruktur von Tetramethylammoniumbromid-Brom-SO2-Addukt, [(CH3)4N]+Br-?Br2?2SO2

“…5 [28,29]. In Salzen mit großen Kationen sind sie in der Regel linear und symmetrisch aufgebaut, mit einem typischen Br-Br-Abstand von 254 pm [30,31]. Diese Abstände sind ähnlich denen im I 16 4Ϫ [29].…”

“…In isolierten Tribromidionen werden solche Abstände in der Regel nicht gefunden[30,31]. U eq ϭ 1 elementaren Brom.…”

Chlorine, Bromine, Iodine and Astatine

“…(d) A trihalide ion varies its symmetry and dimensions according to the demands of its environment, the individual bond distances changing in a systematic way with the overall length of the ion 978 » 981 . This stereochemical flexibility is probably inherent, to some degree, in all polyhalide anions.…”