The Subbromide Bi₅Br₄ – On the Existence of a Hidden Phase

Abstract

Black and irregularly shaped crystals of the bismuth‐rich bromide Bi5Br4 were obtained as a by‐product of the reaction of CsBr, Bi, and BiBr3. X‐ray diffraction on a single‐crystal revealed its orthorhombic structure with the space group Pmmn (no. 59) and lattice parameters a = 1800.0(2) pm, b = 1476.1(1) pm, and c = 924.5(2) pm at 296 K. The structure is composed of Bi82+ and Bi95+ polycations and bromidobismuthate(III) anions according to the structured formula Bi5Br4 = Bi20Br16 = Bi82+Bi95+[BiBr5]2–[Bi2Br11]5–. Bi5Br4 is the bismuth‐richest among the bismuth subhalides containing isolated polycations. Extensive differential scanning calorimetry studies indicate that Bi5Br4 decomposes at 262 °C, i.e. one degree below the bismuth‐rich eutectic at 263 °C. All attempts towards a rational synthesis yielded predominantly the neighboring phases BiBr and Bi6Br7.

Bismuth Polycations Revisited: Alternative Synthesis and Electronic Structure of Bi6Br7, and Bonding in Main-Group Polyatomic Ions from a Direct Space Perspective

“…The first solid compound containing bismuth cluster polycation was bismuth "monochloride" Bi 6 Cl 7 [2], discovered in the early 60s, and the cation was Bi 9 5+ . In the next six decades, other binary and ternary compounds featuring this cation followed [3][4][5][6][7][8][9][10][11][12][13]. A number of other species were also discovered, such as 'classical' Bi 5 3+ [14][15][16][17][18][19] and Bi 8 2+ [13,14,[20][21][22][23][24], and more recent additions Bi 5 + [25,26], Bi 6 2+ [26,27], and Bi 10 4+ , although the latter has not been obtained as a true homoatomic unity and was mostly centered by palladium or platinum, or on rare occasion even by gold [28][29][30][31] (we leave its capped forms outside the scope of this paper as their homoatomic nature is questionable, as well as other heteroatomic bismuth clusters).…”