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 (α_a = 8, α_b = 15 and α_c = 17 × 10⁻⁶ K⁻¹ at 500 K) which is caused by preferential orientation of the borate groups.

中文翻译：

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第一种硼酸铋碘氧化物Bi4BO7I：相称还是相称？

第一种硼酸铋氧碘化物Bi ₄ BO ₇ I是通过在真空二氧化硅安瓿中进行固相反应制得的。它的晶体结构[空间群Immm（00γ）000]包括与边线共享的OBi ₄四面体的利特尔相关层。层间空间中由I填充^-和[BO ₃ ] ^3-阴离子。q  = 0.242（3）c *的波矢非常接近c * / 4的有理值，但基于相称调制的细化面临严重问题，表明调制的不相称性质。I-/ [BO ₃ ] ³⁻阴离子沿着[001]以复杂的顺序排列，即– <– BO ₃ –BO ₃ –I–I–> _{n  = 28} –I–I–I – <– BO ₃ –BO ₃ –I–I–> _{n  = 28} –BO ₃ –BO ₃ –BO ₃ –，导致结构调制。后者的主要特征是–I–I–I–和–BO ₃ –BO ₃ –BO ₃ –序列的存在，这些序列无法在a  × b  ×4 c超级单元中解释。Bi ₄ BO ₇的热膨胀我是弱各向异性（α_一个 = 8，α _b  = 15，α _{C ^}  = 17×10 ^-6  ķ ^-1在500 K）这是由硼酸酯基的择优取向造成的。