Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, USA.
J Am Chem Soc. 2012 Jul 25;134(29):12138-48. doi: 10.1021/ja303370j. Epub 2012 Jul 16.
R(33)Fe(14-x)Al(x+y)B(25-y)C(34) (R = La or Ce; x ≤ 0.9; y ≤ 0.2) and R(33)Fe(13-x)Al(x)B(18)C(34) (R = Ce or Pr; x < 0.1) were synthesized from reactions of iron with boron, carbon, and aluminum in R-T eutectic fluxes (T = Fe, Co, or Ni). These phases crystallize in the cubic space group Im3m (a = 14.617(1) Å, Z = 2, R(1) = 0.0155 for Ce(33)Fe(13.1)Al(1.1)B(24.8)C(34), and a = 14.246(8) Å, Z = 2, R(1) = 0.0142 for Ce(33)Fe(13)B(18)C(34)). Their structures can be described as body-centered cubic arrays of large Fe(13) or Fe(14) clusters which are capped by borocarbide chains and surrounded by rare earth cations. The magnetic behavior of the cerium-containing analogs is complicated by the possibility of two valence states for cerium and possible presence of magnetic moments on the iron sites. Temperature-dependent magnetic susceptibility measurements and Mössbauer data show that the boron-centered Fe(14) clusters in Ce(33)Fe(14-x)Al(x+y)B(25-y)C(34) are not magnetic. X-ray photoelectron spectroscopy data indicate that the cerium is trivalent at room temperature, but the temperature dependence of the resistivity and the magnetic susceptibility data suggest Ce(3+/4+) valence fluctuation beginning at 120 K. Bond length analysis and XPS studies of Ce(33)Fe(13)B(18)C(34) indicate the cerium in this phase is tetravalent, and the observed magnetic ordering at T(C) = 180 K is due to magnetic moments on the Fe(13) clusters.
R(33)Fe(14-x)Al(x+y)B(25-y)C(34)（R = La 或 Ce；x ≤ 0.9；y ≤ 0.2）和 R(33)Fe(13-x)Al(x)B(18)C(34)（R = Ce 或 Pr；x < 0.1）是通过铁与硼、碳和铝在 R-T 共晶熔体（T = Fe、Co 或 Ni）中的反应合成的。这些相在立方空间群 Im3m 中结晶（a = 14.617(1)Å，Z = 2，R(1) = 0.0155 对于 Ce(33)Fe(13.1)Al(1.1)B(24.8)C(34），a = 14.246(8)Å，Z = 2，R(1) = 0.0142 对于 Ce(33)Fe(13)B(18)C(34））。它们的结构可以描述为大 Fe(13)或 Fe(14)簇的体心立方阵列，这些簇由硼碳化物链封端，并被稀土阳离子包围。含铈类似物的磁行为很复杂，因为铈可能有两种价态，并且铁位上可能存在磁矩。温度依赖的磁化率测量和穆斯堡尔数据表明，Ce(33)Fe(14-x)Al(x+y)B(25-y)C(34) 中的硼中心 Fe(14)簇没有磁性。X 射线光电子能谱数据表明，室温下铈为三价，但电阻率和磁化率数据的温度依赖性表明 Ce(3+/4+)价态波动始于 120 K。Ce(33)Fe(13)B(18)C(34) 的键长分析和 XPS 研究表明，该相中铈为四价，在 T(C) = 180 K 观察到的磁有序是由于 Fe(13)簇上的磁矩。
