Crystallographic configurations of water molecules and exchangeable cations in a hydrated natural CHA-zeolite (chabazite)
Crystallographic configurations of water molecules and exchangeable cations in a hydrated natural CHA-zeolite (chabazite)
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DOI：
10.1016/j.micromeso.2006.12.032
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发表时间：
2007-05
影响因子：
5.2
通讯作者：
A. Nakatsuka;Hironao Okada;K. Fujiwara;N. Nakayama;T. Mizota
中科院分区：
文献类型：
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作者：
A. Nakatsuka;Hironao Okada;K. Fujiwara;N. Nakayama;T. Mizota
本文用单晶X射线衍射分析方法研究了天然CHA沸石（菱沸石）（Ca_（1.57）Na_（0.49））（Al_（3.39）Si_（8.55））O_（24）·12.47 H_2 O）中水分子和交换性阳离子的晶体构型。结构分析显示存在5个部分占据的水位点（OW 1-OW 5）和4个部分占据的可交换阳离子位点（Ca 1-Ca 4），并且最终的结构精修对于1255个反射收敛到R=0.0283和Rw=0.0276。在这些位点中，Ca 4和OW 2位点分别位于[4126286]-腔中[4662]-环的中心和8-环窗口的中心，其余位点位于[4126286]-腔中。Ca 1原子只能与水分子配位，完全配位的Ca 1原子可以采用八面体配位或三棱柱配位，这取决于水分子的构型。Ca 2和Ca 3原子既可以与骨架氧原子配位，也可以与水分子配位，完全配位的Ca 2和Ca 3原子可以分别采用七重配位和八面体配位。Ca 4原子通过六个骨架氧原子配位成八面体。从OW O和OW OW距离判断，预计水分子与骨架氧原子之间形成的氢键非常弱，而水分子之间可以存在强氢键。
Crystallographic configurations of water molecules and exchangeable cations in a hydrated natural CHA-zeolite (chabazite) with a composition of (Ca1.57Na0.49)(Al3.39Si8.55)O24·12.47H2O have been examined from the structure analyses based on single-crystal X-ray diffraction data. The structure analyses have revealed the presence of five partially occupied water sites (OW1–OW5) and four partially occupied exchangeable-cation sites (Ca1–Ca4), and the final structure refinement converged to R=0.0283 and Rw=0.0276 for 1255 reflections. Of these sites, the Ca4 and OW2 sites are located at the center of the [4662]-ring and the center of the 8-ring window in the [4126286]-cavity, respectively, and the remaining sites are inside the [4126286]-cavity. The Ca1 atoms can be coordinated only by water molecules, and fully coordinated Ca1 atoms can adopt an octahedral coordination or a triangular-prismatic coordination depending on configurations of water molecules. The Ca2 and Ca3 atoms can be coordinated by both framework oxygen atoms and water molecules, and fully coordinated Ca2 and Ca3 atoms can adopt a sevenfold coordination and an octahedral coordination, respectively. The Ca4 atoms are coordinated octahedrally by six framework oxygen atoms. Judging from OW⋯O and OW⋯OW distances, the hydrogen bonds formed between water molecules and framework oxygen atoms are expected to be very weak, whereas strong hydrogen bonds can exist between water molecules.