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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Exo-bonded six-membered heterocycle in the crystal structures of RE7Co2Ge4 (RE = La-Nd)
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Exo-bonded six-membered heterocycle in the crystal structures of RE7Co2Ge4 (RE = La-Nd)

机译：RE7Co2Ge4（RE = La-Nd）晶体结构中的外键键合六元杂环

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In this article four new ternary phases of RE7Co2Ge4 (RE = La-Nd) are reported. They were synthesized by a solid-state reaction of the elements at high temperature, and their crystal structures were investigated by single crystal X-ray diffraction data. The isostructural phases crystallize in a new monoclinic structure type, space group P2(1)/c, Z = 4, Pearson code mP52, and Wyckoff sequence e(13). They feature planar {Co4Ge6} clusters consisting of a benzene-like six-membered (Co4Ge2) metal heterocycle and four Co-Ge exo-bonds. Band structure calculations were carried out to investigate the electronic structures of La7Co2Ge4, in order to understand the nature of the chemical bonding, and the structure directing factors that determine the atomic ordering and the structure stability. These calculations indicate that the cobalt mid-transition metals are present as (formally) anionic species. They also reveal significant valence electron back-donation from the anionic {Co4Ge6} units to the La-d orbitals through multicenter bonding involving all atoms of the structure, which is key for the structure's stability with respect to incomplete charge transfer. The applicability of the 18 - n rule in rationalizing the Co-Co relative bond strength was also assessed and, the impact of these metal-metal interactions in stabilizing these clusters was described. Similar valence electron back-donation to stabilize further unusual cluster shapes is expected in other rare earth-transition metal-main group phases.
机译：本文报道了RE7Co2Ge4的四个新的三元相（RE = La-Nd）。它们是通过高温下元素的固相反应合成的，并通过单晶X射线衍射数据研究了它们的晶体结构。等结构相结晶为一种新的单斜晶结构类型，空间群P2（1）/ c，Z = 4，皮尔逊码mP52，Wyckoff序列e（13）。它们的特征是平面的{Co4Ge6}簇，由类似苯的六元（Co4Ge2）金属杂环和四个Co-Ge外键构成。进行能带结构计算以研究La7Co2Ge4的电子结构，以了解化学键的性质以及决定原子有序性和结构稳定性的结构指导因素。这些计算表明，钴中间过渡金属以（形式上）阴离子形式存在。他们还揭示了通过涉及结构中所有原子的多中心键合，阴离子{Co4Ge6}单元向La-d轨道显着的价电子给体，这是结构不完整电荷转移的稳定性的关键。还评估了18-n规则在合理化Co-Co相对键强度方面的适用性，并描述了这些金属-金属相互作用对稳定这些簇的影响。在其他稀土过渡金属-主族相中，有望实现类似的价电子返还，以稳定其他不寻常的团簇形状。

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