Department of Chemistry, Durham University, Science Laboratories, South Road, Durham, DH1 3LE UK.
Inorg Chem. 2010 Mar 1;49(5):2290-301. doi: 10.1021/ic902166j.
We report structural investigations into (MoO(2))(2)P(2)O(7) 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 gamma-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) A, b = 6.3095(1) A, c = 10.4161(1) A, and volume 831.87(1) A(3) from synchrotron data at 423 K. The low temperature alpha-structure was indexed from electron diffraction data and contains 60 unique atoms in space group P2(1)/c with cell parameters a = 17.8161(3) A, b = 10.3672(1) A, c = 17.8089(3) A, beta = 90.2009(2) degrees, and volume 3289.34(7) A(3) at 250 K. First principles calculations of (31)P chemical shift and J couplings were used to establish correlation between local structure and observed NMR parameters, and 1D and 2D (31)P solid-state NMR used to validate the proposed crystal structures. The intermediate beta-phase is believed to adopt an incommensurately modulated structure; (31)P NMR suggests a smooth structural evolution in this region.
我们使用 X 射线、中子和电子衍射结合第一性原理量子化学计算，对（MoO(2))(2)P(2)O(7)的结构进行了研究。这些研究揭示了在 377 和 325 K 冷却温度下的一系列相变。高温 γ 相的连接性与 Kierkegaard 在室温下提出的相一致（但键长分布有所改善），并且在空间群 Pnma 中包含 13 个独特的原子，晶格参数为 a = 12.6577(1) A，b = 6.3095(1) A，c = 10.4161(1) A，体积为 831.87(1) A(3)，来自 423 K 时同步加速器数据。低温 α 结构是从电子衍射数据中索引出来的，包含 60 个独特的原子，在空间群 P2(1)/c 中，其细胞参数为 a = 17.8161(3) A，b = 10.3672(1) A，c = 17.8089(3) A，β=90.2009(2)度，体积为 3289.34(7) A(3)，在 250 K。（31）P 化学位移和 J 耦合的第一性原理计算用于建立局部结构与观察到的 NMR 参数之间的相关性，1D 和 2D（31）P 固态 NMR 用于验证所提出的晶体结构。中间的 β 相被认为采用了不相干调制结构；（31）P NMR 表明该区域结构有一个平滑的演化。
