Tzeli Demeter
Laboratory of Physical Chemistry, Department of Chemistry, National and Kapodistrian University of Athens, Athens, Greece.
Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, Athens, Greece.
J Comput Chem. 2021 Jun 15;42(16):1126-1137. doi: 10.1002/jcc.26527. Epub 2021 Apr 14.
Quadruple bonding is uncommon for main group elements and the identification of species forming such bonds is remarkably interesting particularly in diatomic anions for which there is a lack of information. Here, it is found that the MX anions, TcN , RuC , RhB , and PdBe , present quadruple bonding, as do the corresponding MX neutrals, even though a different type of σ bond is involved in ∑ states of neutral and anions. Specifically, the ground states (X Δ or X ∑ ) of the four anions and their first excited states (A ∑ or A Δ) of TcN , RuC , and RhB present quadruple bonds consisting of two σ and two π bonds: (4d - 2p ) , 5p ← 2s , (4d - 2p ) , and (4d - 2p ) . Bond lengths, dissociation energies, spectroscopic data and electron affinities were calculated via high-level multireference and coupled-cluster methodology using the aug-cc-pV5Z (-PP) basis set. Strong bonding results in short bond lengths ranging from 1.602 (TcN ) to 1.944 (PdBe ) Å. Adiabatic (diabatic) binding energies reach up to 139 (184) kcal/mol. Electron affinities (EA) were calculated at 1.368 (TcN), 1.242 (RuC), 0.873 (RhB), 0.743 (PdBe) eV. Only for RhB has EA been measured experimentally at 0.961 eV, in good agreement with the value reported here.
四重键在主族元素中并不常见，因此识别形成此类键的物种非常有趣，尤其是在缺乏相关信息的双原子阴离子中。在此，发现MX阴离子、TcN、RuC、RhB和PdBe存在四重键，相应的MX中性分子也是如此，尽管中性分子和阴离子的∑态涉及不同类型的σ键。具体而言，四种阴离子的基态（XΔ或X∑）及其第一激发态（A∑或AΔ），以及TcN、RuC和RhB的第一激发态都存在由两个σ键和两个π键组成的四重键：(4d – 2p)、5p ← 2s、(4d – 2p)和(4d – 2p)。使用aug-cc-pV5Z(-PP)基组，通过高水平多参考和耦合簇方法计算了键长、解离能、光谱数据和电子亲和能。强键导致键长较短，范围从1.602（TcN）到1.944（PdBe）Å。绝热（非绝热）结合能高达139（184）kcal/mol。计算得到的电子亲和能（EA）分别为1.368（TcN）、1.242（RuC）、0.873（RhB）、0.743（PdBe）eV。只有RhB的EA通过实验测量为0.961 eV，与本文报道的值高度吻合。
