Pressure dependence of the hydrogen-bond geometry in topaz-OD from neutron powder diffraction
Pressure dependence of the hydrogen-bond geometry in topaz-OD from neutron powder diffraction
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DOI：
10.2138/am.2008.2483
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发表时间：
2008-01-01
影响因子：
3.1
通讯作者：
Kudoh, Y.
中科院分区：
文献类型：
--
作者：
Komatsu, K.;Kagi, H.;Kudoh, Y.
用中子粉衍射法测定了在10 Gpa和800℃下合成的氢化黄玉[TOPAZ-OD；Al2SiO4(OD)(2)]的晶体结构。由晶格常数与压强的回归得到的线性轴向压缩系数分别为：β(A)=1.87(1)×10(-3)Gpa(-1)，β(B)=1.71(1)×10(-3)Gpa(-1)，β(C)=2.73(1)×10(-3)Gpa(-1)。环境条件下的中子衍射谱和红外光谱表明，D1位的占有率大于D2位。除了以前报道的氢键供体和受体对之外，还提出了包括D1位、O4-D1中心点O2和O4-D1中心点03的分叉氢键，以及包括D2位、O4-D2中心点O1、O4-D2中心点O2和O4-D2中心点O4的三叉氢键。氢键几何构型的压力依赖关系表明，这些施主和受体对可分为两种类型：(1)作为压力的函数而增强的相互作用(O4-D_1中心点O_3、O_4-D_2中心点O_2和O_4-D_2中心点O_4)和(2)减弱的相互作用(O_4-D_1中心点O_1和O_4-D_2中心点O_1)。这些结果还表明，富F天然黄玉和黄玉-OH的v(OH)行为不同的原因是协同效应、O_4-D_2中心点O_4-D_1中心点O_3以及Al-O_4距离的增大。
The crystal structure of deuterated topaz [topaz-OD; Al2SiO4(OD)(2)], synthesized at 10 GPa and 800 degrees C, has been determined using neutron powder diffraction at pressures up to 7.5 GPa. The linear axial compressibilities obtained from regressions of the lattice constants vs. pressure are beta(a) = 1.87(1) x 10(-3) GPa(-1), beta(b) = 1.71(1) x 10(-3) GPa(-1), and beta(c) = 2.73(1) x 10(-3) GPa(-1). The occupancy of the D1 site was found to be greater than that of D2, as shown independently using neutron diffraction and infrared spectra at ambient conditions. A bifurcated hydrogen bond involving the D1 site, O4-D1 center dot center dot center dot O2 and O4-D 1 center dot center dot center dot O3, and a trifurcated hydrogen bond involving D2 site, O4-D2 center dot center dot center dot O1, O4-D2 center dot center dot center dot O2, and O4-D2 center dot center dot center dot O4 are proposed for hydrogen-bond donor and acceptor pairs in addition to those reported previously. The observed pressure dependences of the hydrogen-bonding geometry show that these donor and acceptor pairs are classifiable into two types of interaction: (1) those that strengthen as a function of pressure (O4-D1 center dot center dot center dot O3, O4-D2 center dot center dot center dot O2, and O4-D2 center dot center dot center dot O4) and (2) those that weaken (O4-D1 center dot center dot center dot O1 and O4-D2 center dot center dot center dot O1). These results also demonstrate that the reason for the contrasting behavior of the v(OH) between F-rich natural topaz and topaz-OH are both the cooperative effect, O4-D2 center dot center dot center dot O4-D1 center dot center dot center dot O3, and the increasing Al-O4 distance.