Structures of Pd(CN)2 and Pt(CN)2: Intrinsically Nanocrystalline Materials?

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• 作者：Simon J. Hibble ; Ann M. Chippindale ; Edward J. Bilbe虂 ; Elena Marelli ; Peter J. F. Harris ; Alex C. Hannon
• 刊名：Inorganic Chemistry
• 出版年：2011
• 出版时间：January 3, 2011
• 年：2011
• 卷：50
• 期：1
• 页码：104-113
• 全文大小：1070K
• 年卷期：v.50,no.1(January 3, 2011)
• ISSN：1520-510X

文摘

Analysis and modeling of X-ray and neutron Bragg and total diffraction data show that the compounds referred to in the literature as 鈥淧d(CN)₂鈥?and 鈥淧t(CN)₂鈥?are nanocrystalline materials containing small sheets of vertex-sharing square-planar M(CN)₄ units, layered in a disordered manner with an intersheet separation of 3.44 脜 at 300 K. The small size of the crystallites means that the sheets' edges form a significant fraction of each material. The Pd(CN)₂ nanocrystallites studied using total neutron diffraction are terminated by water and the Pt(CN)₂ nanocrystallites by ammonia, in place of half of the terminal cyanide groups, thus maintaining charge neutrality. The neutron samples contain sheets of approximate dimensions 30 脜 脳 30 脜. For sheets of the size we describe, our structural models predict compositions of Pd(CN)₂路xH₂O and Pt(CN)₂路yNH₃ (x 鈮?y 鈮?0.29). These values are in good agreement with those obtained from total neutron diffraction and thermal analysis, and are also supported by infrared and Raman spectroscopy measurements. It is also possible to prepare related compounds Pd(CN)₂路pNH₃ and Pt(CN)₂路qH₂O, in which the terminating groups are exchanged. Additional samples showing sheet sizes in the range 10 脜 脳 10 脜 (y 0.67) to 80 脜 脳 80 脜 (p = q 0.12), as determined by X-ray diffraction, have been prepared. The related mixed-metal phase, Pd_1/2Pt_1/2(CN)₂路qH₂O (q 0.50), is also nanocrystalline (sheet size 15 脜 脳 15 脜). In all cases, the interiors of the sheets are isostructural with those found in Ni(CN)₂. Removal of the final traces of water or ammonia by heating results in decomposition of the compounds to Pd and Pt metal, or in the case of the mixed-metal cyanide, the alloy, Pd_1/2Pt_1/2, making it impossible to prepare the simple cyanides, Pd(CN)₂, Pt(CN)₂, or Pd_1/2Pt_1/2(CN)₂, by this method.