Add time:08/03/2019         Source:sciencedirect.com

The compounds A2Fe2Si2C (A=La, Ce, Sm, Th) and A2Re2Si2C (A=Y, La–Nd, Sm, Gd–Er, Th) have been prepared for the first time. They crystallize with the Dy2Fe2Si2C type structure, which was refined for Th2Re2Si2C from single-crystal X-ray data: C2/m, a=1117.82(9) pm, b=417.53(4) pm, c=702.93(7) pm, β=128.721(7)°, Z=2, R=0.023 for 648 structure factors and 22 variable parameters. Some rhenium is present on the silicon site of this compound, resulting in the exact composition Th2Re2.086(4)Si1.914(4)C. The interatomic distances of this structure are compared with those of the previously reported isotypic and isoelectronic compounds Dy2Fe2Si2C and Tm2Fe2Si2C. The Re–Re bonds within the two-dimensionally infinite rhenium-silicon-carbon polyanion are stronger than the Fe–Fe bonds of the iron compound, while all other bonds in the rhenium–silicon–carbon polyanion (Re–Si, Re–C, Si–Si) are weaker than the corresponding bonds of the iron compound. Thus, the electron count of the transition metal atoms may be close to 18 in both structures, in spite of the differing formal charges of the polyanion: (Fe2Si2C)−6 vs. (Re2Si2C)−8.

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