The first bismuth borate oxyiodide, Bi₄BO₇I: commensurate or incommensurate?

Abstract

The first bismuth borate oxyiodide, Bi4BO7I, has been prepared by solid-state reaction in evacuated silica ampoules. Its crystal structure [space group Immm(00γ)000] comprises litharge-related layers of edge-sharing OBi4 tetrahedra; the interlayer space is filled by I− and [BO3]3− anions. The wavevector, q = 0.242 (3)c*, is very close to the rational value of c*/4, yet refinement based on commensurate modulation faces serious problems indicating the incommensurate nature of the modulation. The I-/[BO3]3− anions are ordered in a complex sequence along [001], i.e. –<–BO3–BO3–I–I–> n = 28–I–I–I–<–BO3–BO3–I–I–> n = 28–BO3–BO3–BO3–, leading to a structural modulation. The principal feature of the latter is the presence of –I–I–I– and –BO3–BO3–BO3– sequences that cannot be accounted for in the a × b × 4c supercell. The thermal expansion of Bi4BO7I is weakly anisotropic (αa = 8, αb = 15 and αc = 17 × 10−6 K−1 at 500 K) which is caused by preferential orientation of the borate groups.

When the difference between incommensurate and commensurate structures becomes elusive: the case of Bi4BO7 X (X = Cl, Br) oxyhalides

“…1 and 2). This is a clear indication of incommensurate modulation of pseudotetragonal subcells with a ' 3.93 A ˚, b ' 13.10 A ånd c ' 3.88 A ˚and a modulation vector of q ' 0.245 (5)c* for 1, which is very similar to what was observed for Bi 4 BO 7 I (Volkov et al, 2020). Analysis of the systematic extinctions indicated the superspace group Immm(00)000; satellites of up to third order are observed (Fig.…”

“…The title compounds were prepared in the same way as the related oxyiodide Bi 4 BO 7 I (Volkov et al, 2020). In the first step, BiBO 3 and Bi 3 BO 6 precursors were prepared by slowly heating mixtures of bismuth nitrate pentahydrate and boric acid (extra pure grade) in open alumina crucibles to 723 K (ramp 10 K h À1 , soak 60 h).…”

“…The crystal structures of 1 and 2 were refined using the Immm(00)000 superspace group with the JANA2006 program, starting from the atomic parameters of Bi 4 BO 7 I (Volkov et al, 2020), and they refined to R obs = 0.066 and 0.047, respectively. The bismuth atoms occupy the special 4g Wyckoff site and were refined anisotropically.…”

“…K 3 B 6 O 10 Cl (Wu et al, 2011), Pb 2 B 5 O 9 I (Huang et al, 2010) etc. Recently, we discovered and determined the crystal structure of the first bismuth borate oxyiodide, Bi 4 BO 7 I, which exhibits a complex incommensurate crystal structure (Volkov et al, 2020). The related compounds Bi 4 BO 7 Cl and Bi 4 BO 7 Br have been briefly noted by Egorova (2011).…”

Band engineering of layered oxyhalide photocatalysts for visible-light water splitting

“…Furthermore, blending molecular anions with single anions could lead to a unique structural modulation, as seen in [Bi 2 O 2 ] 2 I(BO 3 ). 145 where the single interlayer anion site is occupied with both I − and BO 3 2− anions. BO 3 2− has a roughly comparable thermochemical radius (191 Å) 146 with Br − (1.96 Å) and I − (2.2 Å).…”