Departamento de Química, Módulo 13, Facultad de Ciencias and Institute for Advanced Research in Chemical Sciences (IAdChem), Universidad Autónoma de Madrid, Madrid 28049, Spain.
Instituto de Química Médica (CSIC), Juan de la Cierva, 3, E-28006 Madrid, Spain.
J Chem Phys. 2022 May 21;156(19):194303. doi: 10.1063/5.0089716.
Although triazoles and tetrazole are amphoteric and may behave as weak acids, the latter property can be hugely enhanced by beryllium bonds. To explain this phenomenon, the structure and bonding characteristics of the complexes between triazoles and tetrazoles with one and two molecules of BeF have been investigated through the use of high-level G4 ab initio calculations. The formation of the complexes between the N basic sites of the azoles and the Be center of the BeF molecule and the (BeF) dimer leads to a significant bonding perturbation of both interacting subunits. The main consequence of these electron density rearrangements is the above-mentioned increase in the intrinsic acidity of the azole subunit, evolving from a typical nitrogen base to a very strong nitrogenous acid. This effect is particularly dramatic when the interaction involves the (BeF) dimer, that is, a Lewis acid much stronger than the monomer. Although the azoles investigated have neighboring N-basic sites, their interaction with the (BeF) dimer yields a monodentate complex. However, the deprotonated species becomes extra-stabilized because a second N-Be bond is formed, leading to a new five-membered ring, with the result that the azole-(BeF) complexes investigated become stronger nitrogenous acids than oxyacids such as perchloric acid.
尽管三唑和四唑是两性的，可能表现为弱酸，但通过铍键可以极大地增强后者的性质。为了解释这一现象，通过使用 G4 从头计算方法研究了三唑和四唑与一个和两个 BeF 分子的配合物的结构和键合特性。唑类化合物的 N 碱性位点与 BeF 分子和（BeF）二聚体的 Be 中心之间形成配合物，导致相互作用的两个亚基的键合发生显著扰动。这些电子密度重排的主要结果是唑亚基固有酸度的上述增加，从典型的氮碱演变为非常强的含氮酸。当相互作用涉及（BeF）二聚体时，即比单体强得多的路易斯酸时，这种效应尤其显著。尽管所研究的唑类化合物具有相邻的 N-碱性位点，但它们与（BeF）二聚体的相互作用生成了单齿配合物。然而，去质子化的物种由于形成了第二个 N-Be 键而得到额外的稳定，导致形成了一个新的五元环，结果是所研究的唑-(BeF)配合物成为比高氯酸等含氧酸更强的含氮酸。
