Extended X-ray absorption fine structure studies of the amorphous tungsten sulfides and selenides, WS5, WSe5 and WS3
作者:Simon J. Hibble、David A. Rice、David M. Pickup、Michael P. Beer
DOI:10.1039/ft9969202131
日期:——
Extended X-ray absorption fine structure (EXAFS) and S K-edge absorption studies of the amorphous tungsten sulfide, WS5, and EXAFS studies of the amorphous tungsten selenide, WSe5, suggest these compounds can be formulated as WV(S22–) and WV(Se22–)2.5. The observed metal–metal distances of ca. 2.75 Å are consistent with the formation of a metal–metal bond between these d1 metal centres; the metal–metal bond would explain the observed diamagnetism of these compounds. The Se—Se bond length of 2.34 Å, determined from the Se K-edge EXAFS studies, is typical of a diselenide group. Comparison of the S K-edge absorption spectrum for WS5 with spectra from related compounds suggests that the sulfur is in the –1 oxidation state. This is in agreement with the observed absorption in the infrared at 518 cm–1 which we assign to an S–S stretch in a disulfide group. The S K-edge absorption spectrum of WS3 suggests that this compound contains both S–I and S–II. W LIII-edge EXAFS studies of WS3 show much greater disorder in the W—S bonding than in WS5, which can be attributed to the presence of sulfur in two oxidation states. Models based on two possible formulations, WV(S2–)2(S22–)0.5 and WIV(S2–)(S22–), give almost equally good fits to the experimental data. The observed diamagnetism of WS3 can be explained by the formation of W—W bonds of ca. 2.75 Å, which are found in the EXAFS studies. Possible structural models for WS5 and WSe5 are presented.
扩展X射线吸收细微结构(EXAFS)和S K边吸收研究表明,非晶态的硫化钨WS5和非晶态的硒化钨WSe5可以被表述为WV(S22–)和WV(Se22–)2.5。这些d1金属中心之间观察到的金属-金属距离约为2.75 Å,这与金属-金属键的形成是一致的;金属-金属键可以解释这些化合物观察到的抗磁性。从Se K边EXAFS研究中确定的Se—Se键长为2.34 Å,这典型于二硒化物组。将WS5的S K边吸收光谱与相关化合物的光谱进行比较,表明硫处于-1氧化态。这与我们在518 cm–1的红外吸收观察结果一致,我们将其归因于二硫化物组中的S–S伸缩振动。WS3的S K边吸收光谱表明,该化合物同时包含S–I和S–II。WS3的W LIII边EXAFS研究显示,W—S键的无序程度远大于WS5,这可以归因于硫存在于两种氧化态。基于两种可能的表示法WV(S2–)2(S22–)0.5和WIV(S2–)(S22–)的模型对实验数据给出了几乎同样好的拟合。WS3观察到的抗磁性可以通过形成约2.75 Å的W—W键来解释,这在EXAFS研究中得以发现。提供了WS5和WSe5的可能结构模型。