担载四核羰基簇——FeCo_3(CO)_11PPh_3^-在聚苯乙烯表面簇骼畸变的EXAFS研究

Immobilized Tetranuclear Carbonyl Cluster——EXAFS Investigation on the Framework Distortion of FeCo_3(CO)_(11)^(?)PPh_(?)^- on the Surface of Polystyrene

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摘要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 aim of anchoring the cobalt-iron tetranuclear carbonyl cluster FeCo_3(CO)_(12)^-on the phosphinated surface of the polystyrene through ligand substitution was to obtain the cluster FeCo_3(CO_(11)PPh_3^-/poly. With its framework departing from the higher symmetrio struoture and to investigate the effects of the anchoring process. The struoture of the immobilized sample was determined by means of EXAFS(Extended Xray Absorption Fine Structure). The result showed that the structural model of the target moleoule was much the same as FeCo_3(CO)_(11)PPh_3^- crystal, especially the phosphine ligand was indeed bonded to one Co atom. It can be found that, (1) in comparison with those of FeCo_3(CO)_(12)^-, the struoture of its framework possesses a threefold symmetry, the bond length of Co-Fe was inoreased 0.005nm; and the Debye-Waller factors of the M-M and M-C_(b) (M=metal; C_(b)=bridging carbon) shells were about two times greater, and that of C_(t)(C_(t)=terminal Carbon) shell, however, remained almost the same. The results imply that the values of the metal-metal bond length were distributed in a wider range, and then the framework was departed from the threefold symmetry. (2) in comparison with the structure of FeCoC3(CO)_(11)PPh_3^-crystal, it was also found that, the Co-Fe bond lergth was 0.003nm longer, and the Co-Co bond length was 0.002nm shorter. Acoording to the fact that the bond lengths derived from EXAFS were only in an average sense, it can be assumed that, after anchoring, the framework distortion in FeCo_3(CO)_(11)PPh_3^- crystal caused by substituting one CO by PPh_3 was enhanced.