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通过配体取代将四核羰基簇FeCo_3(CO)_(12)~-锚联在膦化的聚苯乙烯表面,获得担载簇FeCo(?)(CO)_(11)PPh_3~-/poly,目的在于使簇骼结构偏离较高对称性.以考察锚联过程对簇结构的影响.本文以EXAFS(Extended X-ray Absorption Fine Structure)方法研究了担载样品的结构.结果显示担载簇与FeCo_3(CO)_(11)PPh_3~-晶体具有相同的结构模式,尤其是膦配体确实与一Co原子相连接.EXAFS结果表明:(1)与FoCo_3(CO)_(12)~-(其簇骼具有三重对称性结构)比较,锚联使Co—Fe键增长0.005nm;金属-金属及金属-桥联碳壳层的Debye-Waller因子均增大约一倍而金属-端联碳壳层的值变化很小.说明金属-金属间实际键长值具有一较宽分布,因而其簇骼已偏离了三重对称结构;(2)与FeCo_3(CO)_(11)PPh_3~-晶体的结构比较.Co—Fe键长长0.003nm.而Co—Co键长则短约0.002nm.考虑到EXAFS分析只能给出平均键长值,因此认为,存在于FeCo_3(CO)_(11)PPh_3~-晶体中的由于一个羰基被膦配体取代而引起的簇骼畸变,在锚联后被加剧.
The FeCo (?) (CO) _ (11) PPh_3 ~ - / poly (tetrabutyl titanate) supported cluster was obtained by the tetragonal carbonyl cluster FeCo_3 (CO) _ (12) , The purpose is to shift the cluster structure away from the higher symmetry in order to investigate the effect of the anchoring process on the cluster structure.In this paper, the structure of the loaded sample was studied by EXAFS (Extended X-ray Absorption Fine Structure) The crystal structure of FeCo_3 (CO) _ (11) PPh_3 ~ - crystals is the same as that of FeCo_3 (CO) _ (11) PPh_3 ~ (The cluster has a triple symmetry structure), the Co-Fe bonds were increased by 0.005 nm. The Debye-Waller factor of the metal-metal and metal-bridged carbon shells both increased by about one time. The metal- The value of the shell has little change, indicating that the length of the actual metal-metal bond has a wide distribution and thus the cluster has deviated from the triple symmetry structure. (2) Compared with FeCo3 (CO) _ (11) PPh_3 ~ The Co-Fe bond length is 0.003 nm and the Co-Co bond length is about 0.002 nm. Considering that the average bond length can only be given by EXAFS analysis, it is believed that the Co-Fe bond exists in FeCo 3 (CO) ) PPh_3 ~ - crystals The skeletal distortion due to the substitution of a carbonyl group by a phosphine ligand is exacerbated after anchoring.