Studies on clathrasils. III. Crystal structure of melanophlogite, a natural clathrate compound of silica.
Studies on clathrasils. III. Crystal structure of melanophlogite, a natural clathrate compound of silica.
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笼形硅的研究。
DOI：
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发表时间：
1983
期刊：
影响因子：
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通讯作者：
H. Gies
中科院分区：
文献类型：
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作者：
H. Gies
The high temperature form of melanophlogite, 46 Si02. 6MI4 .2M12(M12 =CH4, N2; M14= C02, N2), is cubic with space group Pm3n and a= 13.436(3) A at 200°C. The mineral is isostructural with the cubic gas hydrates of type 1. Structure refinement with 667 independent reflections led to a weighted Rw= 0.040. Corner-sharing (Si04) tetrahedra form a 3- dimensional framework which contains two types of cages: 2 pentagondo- decahedra (V ~97 A3) and 6 tetrakaidecahedra (V ~ 136 A3) per unit cell. From difference Fourier syntheses it is concluded that the guest molecules MI2 and MI4 within the dodecahedral and tetrakaidecahedral cages are oriented in such a way that the van der Waals contacts between the guest molecules and the Si02 framework are optimized. The mean value of the Si -0 -Si angles (168.8°) is considerably higher and that of the Si -0 distances (1.576A) is considerably lower than corresponding angles and distances in the known silica polymorphs.
