Compounds of Elements in Group

The structure of perfluoroadamantane has been determined by electron diffraction. The effect of fluorination has been to lengthen the C-C bonds by 

There is no modern structural information for silicon tetraiodide, so its structure has now been determined by electron diffraction at 378 K. It is, of course, regularly tetrahedral, and the Si-I bond distance (rg) was determined to be 243.2(5) pm. The non-bonded T T distance refined to 397.1(8) pm. These two distances indicate that there is a very small shrinkage correction in this case. 

In a study of phenyl silane, just five geometrical parameters were determined using the electron diffraction data, the remainder being taken from MP2(fc)/6-31G calculations. The mean C-C distance rf) was 140.3(3) pm, and the bonds adjacent to the silyl substituent were assumed to be 1.0 pm longer than the other bonds, as indicated by the calculations. The Si-C distance was 187.0(4), Si-H 149.7(7) and C-H 110.0(4) pm. The remaining refined parameter was the ring 

The demonstration by electron diffraction that the chair conformation of cyclohexane is preferred to the boat (actually a twisted boat) conformation is one of the classic achievements of the method. Hexasilacyclohexane has similar conformations, but the energy difference between them is much smaller, less than one third as much. Now the structure of an intermediate compound, 1,3,5-trisilacyclohexane, has been determined. The energy gap between the chair and twisted boat conformations is calculated (B3LYP/6-31G ) to be 9.2 kJ mol , similar to that for hexasilacyclohexane (8.0 kJ moF ), but much less than for cyclohexane (27 kJ mol ). The refined Si-C distance, 187.2( 1) pm, and SiCSi and 

CSiC angles, 113.0(4) and 110.7(14)° respectively, determine the ring dihedral angle as 53.7(4)°, smaller than in both cyclohexane (55.1°) and hexasilacyclo-hexane (57.9°). The ring is thus flatter than those of both of its parent compounds, apparently a consequence of the relatively wide SiCSi angle. 

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The most developed and useful inorganic membranes are ceramic ones [24, 25]. Ceramics can be defined as polycrystalline consolidated materials based on compounds of elements in groups III and VI of the periodic table. 

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