“Hexagonal Molybdenum Trioxide”—Known for 100 Years and Still a Fount of New Discoveries

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• 作者：Hans-Joachim Lunk ; Hans Hartl ; Monika A. Hartl ; Martin J. G. Fait ; Ilya G. Shenderovich ; Michael Feist ; Timothy A. Frisk ; Luke L. Daemen ; Daniel Mauder ; Reinhard Eckelt ; Andrey A. Gurinov
• 刊名：Inorganic Chemistry
• 出版年：2010
• 出版时间：October 18, 2010
• 年：2010
• 卷：49
• 期：20
• 页码：9400-9408
• 全文大小：1059K
• 年卷期：v.49,no.20(October 18, 2010)
• ISSN：1520-510X

文摘

In 1906, the preparation of “molybdic acid hydrate” was published by Arthur Rosenheim. Over the past 40 years, a multitude of isostructural compounds, which exist within a wide phase range of the system MoO₃−NH₃−H₂O, have been published. The reported molecular formulas of “hexagonal molybdenum oxide” varied from MoO₃ to MoO₃·0.33NH₃ to MoO₃·nH₂O (0.09 ≤ n ≤ 0.69) to MoO₃·mNH₃·nH₂O (0.09 ≤ m ≤ 0.20; 0.18 ≤ n ≤ 0.60). Samples, prepared by the acidification route were investigated using thermal analysis coupled online to a mass spectrometer for evolved gas analysis, X-ray powder diffraction, Fourier transform infrared, Raman, magic-angle-spinning ¹H- and ¹⁵N NMR spectroscopy, and incoherent inelastic neutron scattering. A comprehensive characterization of these samples will lead to a better understanding of their structure and physical properties as well as uncover the underlying relationship between the various compositions. The synthesized polymeric parent samples can be represented by the structural formula (NH₄)_x∞³[Mo_y1−yO_3y(OH)_x(H₂O)_m−n]·nH₂O with 0.10 ≤ x ≤ 0.14, 0.84 ≤ y ≤ 0.88, and m + n ≥ 3 − x − 3y. The X-ray study of a selected monocrystal confirmed the presence of the well-known 3D framework of edge- and corner-sharing MoO₆ octahedra. The colorless monocrystal crystallizes in the hexagonal system with space group P6₃/m, Z = 6, and unit cell parameters of a = 10.527(1) Å, c = 3.7245(7) Å, V = 357.44(8) ų, and ρ = 3.73 g·cm⁻³. The structure of the prepared monocrystal can best be described by the structural formula (NH₄)_0.13∞³[Mo_0.860.14O_2.58(OH)_0.13(H₂O)_0.29−n]·nH₂O, which is consistent with the existence of one vacancy () for six molybdenum sites. The sample MoO₃·0.326NH₃·0.343H₂O, prepared by the ammoniation of a partially dehydrated MoO₃·0.170NH₃·0.153H₂O with dry gaseous ammonia, accommodates NH₃ in the hexagonal tunnels, in addition to [NH₄]⁺ cations and H₂O. The “chimie douce” reaction of MoO₃·0.155NH₃·0.440H₂O with a 1:1 mixture of NO/NO₂ at 100 °C resulted in the synthesis of MoO₃·0.539H₂O. This material is of great interest as a host of various molecules and cations.