Vos Eva, Corral Inés, Montero-Campillo M Merced, Mó Otilia, Elguero José, Alkorta Ibon, Yáñez Manuel
Departamento de Química (Módulo 13, Facultad de Ciencias) and Institute of Advanced Chemical Sciences (IadChem), Universidad Autónoma de Madrid, Campus de Excelencia UAM-CSIC, Cantoblanco, 28049-Madrid, Spain.
Phys Chem Chem Phys. 2021 Mar 21;23(11):6448-6454. doi: 10.1039/d0cp06009g. Epub 2021 Mar 15.
High-level single and multireference ab initio calculations show that the Be cluster behaves as a very efficient Lewis acid when interacting with conventional Lewis bases such as ammonia, water or hydrogen fluoride, to the point that the corresponding acid-base interaction triggers a sequential dissociation of all the bonds of the Lewis base. Notably, this behavior is already found for the simplest beryllium cluster, the Be dimer. However, whereas for Be the first dissociation process involves a low activation barrier which is above the reactants, for Be all the bond dissociation processes involve barriers below the entrance channel leading to a cascade of successive exothermic processes, which end up spontaneously in a global minimum in which the bonding patterns of both the base and the Lewis acid are completely destroyed. Indeed, the global minimum, in all cases, is stabilized by three-center Be-H-Be bonds and covalent interactions between the Be atoms and the basic center of the base, which replace the initial metallic bond stabilizing the Be cluster. As a consequence, in the global minimum the basic atoms (N, O and F) behave as hyper-coordinated centers. Also importantly, the Be cluster and its complexes present RHF-UHF instabilities (not reported before for Be), which require the use of multireference methods to correctly describe them.
高水平的单参考和多参考从头算计算表明，铍簇在与传统的路易斯碱（如氨、水或氟化氢）相互作用时，表现为一种非常有效的路易斯酸，以至于相应的酸碱相互作用会引发路易斯碱所有键的顺序解离。值得注意的是，在最简单的铍簇——铍二聚体中就已经发现了这种行为。然而，对于铍来说，第一个解离过程涉及一个高于反应物的低活化能垒，而对于铍，所有的键解离过程都涉及低于入口通道的能垒，导致一系列连续的放热过程，最终自发地达到一个全局最小值，在这个最小值中，碱和路易斯酸的键合模式都被完全破坏。事实上，在所有情况下，全局最小值都是由三中心Be-H-Be键以及铍原子与碱的碱性中心之间的共价相互作用稳定的，这些相互作用取代了最初稳定铍簇的金属键。因此，在全局最小值中，碱性原子（N、O和F）表现为超配位中心。同样重要的是，铍簇及其配合物存在RHF-UHF不稳定性（此前未报道过铍的这种情况），这需要使用多参考方法来正确描述它们。
