Mozharivskyj Yurij, Choe Wonyoung, Pecharsky Alexandra O, Miller Gordon J
Ames Laboratory, Iowa State University, Ames, Iowa 500110, USA.
J Am Chem Soc. 2003 Dec 10;125(49):15183-90. doi: 10.1021/ja037649z.
X-ray single crystal and powder diffraction studies on the Gd(5)Ga(x)()Ge(4)(-)(x)() system with 0 < or = x < or = 2.2 reveal dependence of interslab T-T dimer distances and crystal structures themselves on valence electron concentration (T is a mixture of Ga and Ge atoms). While the Gd(5)Ga(x)()Ge(4)(-)(x)() phases with 0 < or = x < or = 0.6 and valence electron concentration of 30.4-31 e(-)/formula crystallize with the Sm(5)Ge(4)-type structure, in which all interslab T-T dimers are broken (distances exceeding 3.4 A), the phases with 1 < or = x < or = 2.2 and valence electron concentration of 28.8-30 e-/formula adopt the Pu(5)Rh(4)- or Gd(5)Si(4)-type structures with T-T dimers between the slabs. An orthorhombic Pu(5)Rh(4)-type structure, which is intermediate between the Gd(5)Si(4)- and Sm(5)Ge(4)-type structures, has been identified for the Gd(5)GaGe(3) composition. Tight-binding linear-muffin-tin-orbital calculations show that substitution of three-valent Ga by four-valent Ge leads to larger population of the antibonding states within the dimers and, thus, to dimer stretching and eventually to dimer cleavage.
对0≤x≤2.2的Gd(5)Ga(x)()Ge(4)( - )(x)()体系进行的X射线单晶和粉末衍射研究表明，板间T - T二聚体距离和晶体结构本身对价电子浓度有依赖性（T是Ga和Ge原子的混合物）。当0≤x≤0.6且价电子浓度为30.4 - 31 e(-)/化学式单位的Gd(5)Ga(x)()Ge(4)( - )(x)()相以Sm(5)Ge(4)型结构结晶时，其中所有板间T - T二聚体均断裂（距离超过3.4 Å），而1≤x≤2.2且价电子浓度为28.8 - 30 e-/化学式单位的相采用板间具有T - T二聚体的Pu(5)Rh(4) - 或Gd(5)Si(4)型结构。已确定Gd(5)GaGe(3)组成具有正交晶系的Pu(5)Rh(4)型结构，它介于Gd(5)Si(4) - 和Sm(5)Ge(4)型结构之间。紧束缚线性 muffin - tin轨道计算表明，用四价Ge取代三价Ga会导致二聚体内反键态的占据数增加，从而导致二聚体拉伸并最终导致二聚体断裂。
