Crystal structures of deuterated sodium molybdate dihydrate and sodium tungstate dihydrate from time-of-flight neutron powder diffraction.
Crystal structures of deuterated sodium molybdate dihydrate and sodium tungstate dihydrate from time-of-flight neutron powder diffraction.
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DOI：
10.1107/s2056989015011354
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发表时间：
2015-07-01
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通讯作者：
Fortes AD
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作者：
Fortes AD
基于高分辨飞行时间中子粉末衍射数据的精细化，报道了Na 2 MoO 4·2D 2 O和Na 2 WO 4·2D 2 O的高精度结构参数。还提供了互补的拉曼光谱。已在295 K下测量了Na 2 MoO 4·2 H2O和Na 2 WO 4·2 H2O的~ 90mol%氘化同位素的飞行时间中子粉末衍射数据，分辨率为sin（θ）/λ = 0.77 Å-1。 中子的使用使得结构参数的精确度可以从最重的原子到最轻的原子变化两倍;这与基于X射线的精确度形成对比，其中在存在Mo和W等原子的情况下，O原子的精确度可能会差20倍以上。原子间距离和角度的精确度和精确度与最近的X射线单晶结构改进非常一致，同时也完成了我们对氢键几何形状的看法，达到了相同的统计确定性程度。这两种结构是同型的，空间群Pbca，所有原子占据一般位置，由共享边和角的NaO 5和NaO 6多面体组成，这些多面体形成与（010）平行的层，与通过水分子链沿着[100]和[001]连接的XO 4（X = Mo，W）四面体平面交错。完整的结构与先前描述的结构相同[Capitelli et al.（2006）. Asian J. Chem. 18，2856-2860]，但表明涉及钨酸盐中的一种水分子的所谓的三中心相互作用[Farrugia（2007）. Acta Cryst. E63，i142]实际上是一个普通的双中心“线性”氢键。
High-precision structural parameters for Na2MoO4·2D2O and Na2WO4·2D2O are reported based on refinement of high-resolution time-of-flight neutron powder diffraction data. Complementary Raman spectra are also provided. Time-of-flight neutron powder diffraction data have been measured from ∼90 mol% deuterated isotopologues of Na2MoO4·2H2O and Na2WO4·2H2O at 295 K to a resolution of sin (θ)/λ = 0.77 Å−1. The use of neutrons has allowed refinement of structural parameters with a precision that varies by a factor of two from the heaviest to the lightest atoms; this contrasts with the X-ray based refinements where precision may be > 20× poorer for O atoms in the presence of atoms such as Mo and W. The accuracy and precision of interatomic distances and angles are in excellent agreement with recent X-ray single-crystal structure refinements whilst also completing our view of the hydrogen-bond geometry to the same degree of statistical certainty. The two structures are isotypic, space-group Pbca, with all atoms occupying general positions, being comprised of edge- and corner-sharing NaO5 and NaO6 polyhedra that form layers parallel with (010) interleaved with planes of XO4 (X = Mo, W) tetrahedra that are linked by chains of water molecules along [100] and [001]. The complete structure is identical with the previously described molybdate [Capitelli et al. (2006). Asian J. Chem. 18, 2856–2860] but shows that the purported three-centred interaction involving one of the water molecules in the tungstate [Farrugia (2007). Acta Cryst. E63, i142] is in fact an ordinary two-centred ‘linear’ hydrogen bond.