You Tae-Soo, Grin Yuri, Miller Gordon J
Department of Chemistry, Iowa State University, Ames, Iowa 50010, USA.
Inorg Chem. 2007 Oct 15;46(21):8801-11. doi: 10.1021/ic701111e. Epub 2007 Sep 20.
The ternary polar intermetallic compounds EuGaTt (Tt = Si, Ge, Sn) have been synthesized and characterized experimentally, as well as theoretically. EuGaSi crystallizes in the hexagonal AlB(2)-type structure (space group P6/mmm, Z = 1, Pearson symbol hP3) with randomly distributed Ga and Si atoms on the graphite-type planes: a = 4.1687(6) A, c = 4.5543(9) A. On the other hand, EuGaGe and EuGaSn adopt the hexagonal YPtAs-type structure (space group P6(3)/mmc, Z = 4, Pearson symbol hP12): a = 4.2646(6) A and c = 18.041(5) A for EuGaGe; a = 4.5243(5) A and c = 18.067(3) A for EuGaSn. The three crystal structures contain formally GaTt polyanionic 3-bonded, hexagonal networks, which change from planar to puckered and exhibit a significant decrease in interlayer Ga-Ga distances as the size of Tt increases. Magnetic susceptibility measurements of this series of compounds show Curie-Weiss behavior above 86(5), 95(5), and 116(5) K with magnetic moments of 7.93, 7.97, and 7.99 mu(B) for EuGaSi, EuGaGe, and EuGaSn, respectively, indicating a 4f(7) electronic configuration (Eu(2+)) for Eu atoms. X-ray absorption spectra (XAS) are also consistent with these magnetic properties. Electronic structure calculations supplemented by a crystal orbital Hamilton population (COHP) analysis identifies the synergy between atomic sizes, from both Eu and Tt atoms, and the orbital contributions from Eu toward influencing the structural features of EuGaTt. A multicentered interaction between planes of Eu atoms and the GaTt layers rather than through-space Ga-Ga bonding is seen in ELF distributions.
三元极性金属间化合物EuGaTt（Tt = Si、Ge、Sn）已通过实验和理论方法进行了合成与表征。EuGaSi以六方AlB₂型结构（空间群P6/mmm，Z = 1，皮尔逊符号hP3）结晶，Ga和Si原子在石墨型平面上随机分布：a = 4.1687(6) Å，c = 4.5543(9) Å。另一方面，EuGaGe和EuGaSn采用六方YPtAs型结构（空间群P6₃/mmc，Z = 4，皮尔逊符号hP12）：EuGaGe的a = 4.2646(6) Å，c = 18.041(5) Å；EuGaSn的a = 4.5243(5) Å，c = 18.067(3) Å。这三种晶体结构均包含形式上为[GaTt]²⁻的多阴离子三键合六方网络，随着Tt尺寸的增加，该网络从平面变为褶皱状，且层间Ga - Ga距离显著减小。对这一系列化合物的磁化率测量表明，在86(5)、95(5)和116(5) K以上呈现居里 - 外斯行为，EuGaSi、EuGaGe和EuGaSn的磁矩分别为7.93、7.97和7.99 μB，表明Eu原子具有4f⁷电子构型（Eu²⁺）。X射线吸收光谱（XAS）也与这些磁性性质一致。通过晶体轨道哈密顿布居（COHP）分析补充的电子结构计算确定了Eu和Tt原子的原子尺寸之间的协同作用，以及Eu的轨道贡献对EuGaTt结构特征的影响。在电子定域函数（ELF）分布中可以看到Eu原子平面与[GaTt]²⁻层之间存在多中心相互作用，而非通过空间的Ga - Ga键合。
