Refinement of the crystal structure of fresnoite, Ba₂TiSi₂O₈, from Löhley (Eifel district, Germany); Gladstone-Dale compatibility, electronic polarizability and vibrational spectroscopy of minerals and inorganic compounds with pentacoordinated Ti^IV and a titanyl bond.

IF 1.3 3区化学 Q3 CHEMISTRY, MULTIDISCIPLINARY

Acta crystallographica Section B, Structural science, crystal engineering and materials Pub Date : 2023-04-01 DOI:10.1107/S2052520622012045

Nikita V Chukanov, Olga N Kazheva, Reinhard X Fischer, Sergey M Aksenov

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Abstract

Most known compounds with five-coordinated Ti⁴⁺ are natural and synthetic titanosilicates. The crystal structure of natural fresnoite, Ba₂TiSi₂O₈ [tetragonal, space group P4bm, a = 8.510 (1) Å, c = 5.197 (1) Å, V = 376.4 (1) Å³, Z = 2], has been refined to R = 0.011 on the basis of 807 unique single-crystal reflections with I > 2σ(I). Titanium has fivefold coordination with one short (`titanyl') bond of 1.692 (5) Å. Bonds in the TiO₅ polyhedron are discussed in comparison to analogous coordination polyhedra in other minerals and compounds. A review of all known compounds with Ti⁴⁺O₅ polyhedra shows that most of them are titanosilicates in which titanium forms a short Ti-O bond (∼1.61 to ∼1.77 Å). Poor Gladstone-Dale compatibility between chemical composition, optical characteristics and density of these compounds is explained by the anomalous contribution of ^[5]Ti⁴⁺ to the optical properties as shown by calculations based on the relationship between electronic polarizabilities and refractive indices. An improved Gladstone-Dale coefficient of 0.29 is suggested for TiO₂ with ^[5]Ti⁴⁺. A negative correlation between `titanyl' bond lengths and wavenumbers of the bands of Ti-O stretching vibrations (in the range of 890-830 cm^-1) in infrared and Raman spectra is observed.

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fresnoite, Ba2TiSi2O8晶体结构的细化，来自Löhley (Eifel district, Germany)具有五配位TiIV和钛基键的矿物和无机化合物的Gladstone-Dale相容性、电子极化率和振动光谱。

大多数已知的五配位Ti4+化合物是天然的和合成的钛硅酸盐。天然fresnoite的晶体结构Ba2TiSi2O8[四边形，空间群P4bm, a = 8.510 (1) Å， c = 5.197 (1) Å， V = 376.4 (1) Å3, Z = 2]，在807个I > 2σ(I)的唯一单晶反射的基础上，将其细化为R = 0.011。钛具有五重配位，一个短键(“钛基”)的键值为1.692 (5)Å。讨论了TiO5多面体中的键与其他矿物和化合物中的类似配位多面体的比较。对所有已知的Ti4+O5多面体化合物的回顾表明，它们中的大多数是钛硅酸盐，其中钛形成一个短的Ti-O键(~ 1.61 ~ ~ 1.77 Å)。这些化合物的化学成分、光学特性和密度之间的差的Gladstone-Dale相容性可以用[5]Ti4+对光学特性的异常贡献来解释，这是基于电子极化率和折射率之间关系的计算所显示的。[5]Ti4+对TiO2的Gladstone-Dale系数提高到0.29。在红外和拉曼光谱中，“钛基”键长与Ti-O拉伸振动带(在890-830 cm-1范围内)的波数呈负相关。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Acta crystallographica Section B, Structural science, crystal engineering and materials CHEMISTRY, MULTIDISCIPLINARYCRYSTALLOGRAPH-CRYSTALLOGRAPHY

CiteScore

3.60

自引率

5.30%

发文量

期刊介绍： Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials publishes scientific articles related to the structural science of compounds and materials in the widest sense. Knowledge of the arrangements of atoms, including their temporal variations and dependencies on temperature and pressure, is often the key to understanding physical and chemical phenomena and is crucial for the design of new materials and supramolecular devices. Acta Crystallographica B is the forum for the publication of such contributions. Scientific developments based on experimental studies as well as those based on theoretical approaches, including crystal-structure prediction, structure-property relations and the use of databases of crystal structures, are published.