英国曼彻斯特大学Stephen T. Liddle研究组近日发现了一种具有σ-芳环间金属-金属键的晶态三钍团簇。这一研究成果于2021年8月23日发表在国际顶尖学术期刊《自然》上。
在该研究中，课题组在常规实验条件下制备和分离了含钍-钍键晶态团簇。该团簇表现出一个反磁的、封闭壳层的单线态基态，其具有价电子离域的三中心双电子σ-芳香键，这与先前的理论预测的焦点相反。这是研究人员首次在主基和过渡金属类似物之外发现锕系元素中的σ-芳香键，这一发现将离域的σ-芳香键扩展到元素周期表中主量子数为6的最重的元素，为进一步阐述锕系-锕系金属键提供了新的方法。
据了解，金属-金属键合是化学中的一个广泛的研究领域，其已经成为一个涉及许多过渡金属和主基配合物成熟领域。相比之下，锕系-锕系金属键在预测中被认为较弱，在此前仅限于通过光谱检测到气相中的U2和Th2，6-7 K低温下冻结基质中的U2H2和U2H4，以及富勒烯包封的U2中。相反，试图在冷冻基质中制备钍-钍键只能产生ThHn (n = 1-4)。因此，此前在正常条件下没有可分离的锕系-锕系金属键。计算研究已经探索了锕系-锕系元素成键的可能性质，并集中于与d区过渡金属类似物平行的局域σ-、π-和δ-成键模型，但在相对论机制下的预测是具有挑战性的，且未得到过实验验证。
附：英文原文
Title: A Crystalline Tri-thorium Cluster with σ-Aromatic Metal-Metal Bonding
Author: Boronski, Josef T., Seed, John A., Hunger, David, Woodward, Adam W., van Slageren, Joris, Wooles, Ashley J., Natrajan, Louise S., Kaltsoyannis, Nikolas, Liddle, Stephen T.
Issue&Volume: 2021-08-23
Abstract: Metal-metal bonding is a widely studied area of chemistry1–3, and has become a mature field spanning numerous d transition metal and main group complexes4–7. In contrast, actinide-actinide bonding is predicted to be weak8, being currently restricted to spectroscopically-detected gas-phase U2 and Th29,10, U2H2 and U2H4 in frozen matrices at 6-7 Kelvin (K)11,12, or fullerene-encapsulated U213. Conversely, attempts to prepare thorium-thorium bonds in frozen matrices produced only ThHn (n = 1-4)14. Thus, there are no isolable actinide-actinide bonds under normal conditions. Computational investigations have explored the likely nature of actinide-actinide bonding15, concentrating on localised σ-, π-, and δ-bonding models paralleling d transition metal analogues, but predictions in relativistic regimes are challenging and have remained experimentally unverified. Here, we report thorium-thorium bonding in a crystalline cluster, prepared and isolated under normal experimental conditions. The cluster exhibits a diamagnetic, closed-shell singlet ground-state with a valence-delocalised three-centre-two-electron σ-aromatic bond16,17 that is counter to the focus of previous theoretical predictions. The experimental discovery of actinide σ-aromatic bonding adds to main group and d transition metal analogues, extending delocalised σ-aromatic bonding to the heaviest elements in the periodic table and to principal quantum number six, and constitutes a new approach to elaborating actinide-actinide bonding.
DOI: 10.1038/s41586-021-03888-3
Source: https://www.nature.com/articles/s41586-021-03888-3