Structures and Phase Transitions in (MoO2)2P2O7

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• 作者：Sarah E. Lister ; Anne Soleilhavoup ; Ray L. Withers ; Paul Hodgkinson ; John S. O. Evans
• 刊名：Inorganic Chemistry
• 出版年：2010
• 出版时间：March 1, 2010
• 年：2010
• 卷：49
• 期：5
• 页码：2290-2301
• 全文大小：1214K
• 年卷期：v.49,no.5(March 1, 2010)
• ISSN：1520-510X

文摘

We report structural investigations into (MoO₂)₂P₂O₇ using a combination of X-ray, neutron and electron diffraction, and solid-state NMR supported by first principles quantum chemical calculations. These reveal a series of phase transitions on cooling at temperatures of 377 and 325 K. The high temperature γ-phase has connectivity consistent with that proposed by Kierkegaard at room temperature (but with improved bond length distribution), and contains 13 unique atoms in space group Pnma with lattice parameters a = 12.6577(1) Å, b = 6.3095(1) Å, c = 10.4161(1) Å, and volume 831.87(1) ų from synchrotron data at 423 K. The low temperature α-structure was indexed from electron diffraction data and contains 60 unique atoms in space group P2₁/c with cell parameters a = 17.8161(3) Å, b = 10.3672(1) Å, c = 17.8089(3) Å, β = 90.2009(2)°, and volume 3289.34(7) ų at 250 K. First principles calculations of ³¹P chemical shift and J couplings were used to establish correlation between local structure and observed NMR parameters, and 1D and 2D ³¹P solid-state NMR used to validate the proposed crystal structures. The intermediate β-phase is believed to adopt an incommensurately modulated structure; ³¹P NMR suggests a smooth structural evolution in this region.