Klem M T, Vaughey J T, Harp J G, Corbett J D
Department of Chemistry and Ames Laboratory-DOE, Iowa State University, Ames, IA 50011, USA.
Inorg Chem. 2001 Dec 31;40(27):7020-6. doi: 10.1021/ic010804v.
A series of compounds that contain square pyramidal Tt(5) polyanions of tin and lead has been obtained in alkaline-earth or rare-earth metal-tetrel systems by direct fusion of the elements at 570 degrees C (Sr(3)Sn(5)), 1000 degrees C (Ba(3)Pb(5)), or 1300 degrees C (La(3)Sn(5)) followed by slow cooling or annealing. The crystal structures for all three have been refined in the Pu(3)Pd(5) structure type (orthorhombic, Cmcm, Z = 4) with cell dimensions of a = 10.644(2), 11.154(7), and 10.352(5) A, b = 8.588(1), 9.049(7), and 8.290(6) A, and c = 10.895(2), 11.370(5), and 10.652(5) A for Sr(3)Sn(5), Ba(3)Pb(5), and La(3)Sn(5), respectively. Square pyramidal clusters of the tetrel elements are weakly interlinked into chains via two types of longer intercluster interactions that are mediated by bridging cations and substantially influenced by cation size and the free electron count. The new compounds are all metallic (rho(295) approximately 10 (Sr(3)Sn(5)) to approximately 25 (La(3)Sn(5)) muOmega.cm), in agreement with simple valence considerations that predict two and five extra electrons per formula unit, respectively, beyond that necessary for closed-shell nido-Tt(5)(4)(-) anions. Extended Hückel tight-binding calculations on the new compounds as well as on La(3)In(5) reveal that bonding in the regions below and around the Fermi energies are dominated by general cation-anion interactions, that is, lattice covalency. Closed-shell bonding features for the classical Sn(5)(4)(-), In(5)(9)(-), etc. ions are also obvious but subsidiary to the heteroatomic interactions with the cations. The intercluster contacts are relatively unimportant in bonding.
通过在570℃（Sr₃Sn₅）、1000℃（Ba₃Pb₅）或1300℃（La₃Sn₅）下直接熔融元素，随后缓慢冷却或退火，在碱土金属或稀土金属 - 四价元素体系中获得了一系列包含锡和铅的正方锥型Tt(5)多阴离子的化合物。这三种化合物的晶体结构均已按照Pu₃Pd₅结构类型（正交晶系，Cmcm，Z = 4）进行精修，对于Sr₃Sn₅、Ba₃Pb₅和La₃Sn₅，其晶胞参数分别为a = 10.644(2)、11.154(7)和10.352(5) Å，b = 8.588(1)、9.049(7)和8.290(6) Å，c = 10.895(2)、11.370(5)和10.652(5) Å。四价元素的正方锥型簇通过两种较长的簇间相互作用微弱地连接成链，这两种相互作用由桥连阳离子介导，并受到阳离子大小和自由电子数的显著影响。这些新化合物均为金属性的（ρ(295)约为10（Sr₃Sn₅）至约25（La₃Sn₅）μΩ·cm），这与简单的化合价考虑相符，即每个化学式单元分别预测有两个和五个额外电子，超出了闭壳层nido - Tt(5)⁴⁻阴离子所需的电子数。对新化合物以及La₃In₅进行的扩展休克尔紧束缚计算表明，在费米能以下及周围区域的键合主要由一般的阳离子 - 阴离子相互作用主导，即晶格共价性。经典的Sn(5)⁴⁻、In(5)⁹⁻等离子的闭壳层键合特征也很明显，但相对于与阳离子的杂原子相互作用而言是次要的。簇间接触在键合中相对不重要。
