Quadruple chemical bonding in the diatomic anions TcN⁻, RuC⁻, RhB⁻, and PdBe⁻

Abstract

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

Electronic Structure and Chemical Bonding of the First-, Second-, and Third-Row-Transition-Metal Monoborides: The Formation of Quadruple Bonds in RhB, RuB, and TcB

“…These bonding schemes depend on the bonding and the filling of σ, π, and δ orbitals. MBs can form one-and-a-half, double, triple, and even quadruple bonds, with the latter being recently discovered in RhB and RhB − [2,4,5], while here, we found that RuB and TcB also form quadruple bonds.…”

“…Any differences are related to the differences in the bonding; see Figure 4b. The smallest differences among the three rows are observed in d 1 s 2 , (ds) 5 , and d 10 s 2 , while the first and third rows present similar µ values for the d 5 s 2 metals, where the second-row MB presents a µ value larger by 1.5 D than the corresponding MnB and ReB values due to the quadruple bond of TcB. In Figure 4d,e, the dissociation energies with respect to the adiabatic products (De) and the atomic ground state products at the zero-vibrational level (D0,GS) are plotted with respect to the change in the M atom from left to right for the three rows.…”

“…Tzeli and Karapetsas [4] found that, except for the ground state of RhB, its two lowest excited states, i.e., a 3 ∆ and A 1 ∆, also present quadruple bonds [4]. Additionally, in the ground and the first excited states of the RhB − anion, X 2 Σ + and A 2 ∆ quadruple bonds are also formed [5]. In 2021, Schoendorff et al [42] also studied the bonding in RhB both qualitatively and quantitively at a MCSCF-IOTC/DKH-TZP-2012 Rh /Sapporo-TZP-2012 B level of theory and reached the same results as those in previous works.…”

“…The dissociation energy of the ground state with the atomic ground state atoms is 3.894 eV; see discussion below. The lowest quintet and septet states are of Σ − symmetry, i.e., 5 Σ − , and 7 Σ − , and they lie 0.312 eV and 2.512 eV above the ground state. They are adiabatically correlated with the Tc( 6 S[4d 5 5s 2 ]) + B( 3 P) dissociation channel, but at equilibrium, the Tc atom is excited at the Tc( 6 D[4d 6 ( 5 D)5s]) + B( 3 P) channel.…”

“…Boron has an important role in chemistry, biology, and materials science [1]. It is well known that it forms single, double, and triple bonds, but it was only recently found that it can form quadruple bonds in specific diatomic molecules [2][3][4][5]. Additionally, its chemistry is quite interesting to preparative chemists, theoreticians, industrial chemists, and technologists.…”