Ordering Double Perovskite Hydroxides by Kinetically Controlled Aqueous Hydrolysis

详细信息    查看全文

• 作者：James R. Neilson ; Joshua A. Kurzman ; Ram Seshadri ; Daniel E. Morse
• 刊名：Inorganic Chemistry
• 出版年：2011
• 出版时间：April 4, 2011
• 年：2011
• 卷：50
• 期：7
• 页码：3003-3009
• 全文大小：967K
• 年卷期：v.50,no.7(April 4, 2011)
• ISSN：1520-510X

文摘

The precipitation of crystals with stoichiometric and ordered arrangements of distinct metal cations often requires carefully designed molecular precursors and/or sufficient activation energy in addition to the necessary mass transport. Here, we study the formation of ordered double perovskite hydroxides, MnSn(OH)₆ and CoSn(OH)₆, of the generic chemical formula, BB鈥?/i>(OH)₆ (no A site), using kinetic control of aqueous hydrolysis from simple metal salt solutions. We find that the precipitation yields ordered compounds only when the B ion is Mn(II) or Co(II), and not when it is any other divalent transition metal ion, or Zn(II). The key step in forming the compounds is the prevention of rapid and uncontrolled hydrolysis of Sn(IV), and this is achieved by a fluoride counteranion. The two compounds, MnSn(OH)₆ and CoSn(OH)₆, are studied by high-resolution synchrotron X-ray diffraction and from the temperature dependence of magnetic behavior. From maximum entropy image restoration of the electron density and from Rietveld analysis, the degree of octahedral distortion and tilting and the small extent of anti-site disorder are determined. From the nonoverlapping electron density, we infer strongly ionic character of bonding. As the first magnetic study of such materials, we report simple paramagnetic behavior with no long-range magnetic order down to 2 K for the Mn(II) compound, while the cobalt compound presents uncompensated antiferromagnetic interactions, attributed to the single-ion anisotropy of octahedral Co(II).