Molybdenum–Sulfur Bond: Electronic Structure of Low-Lying States of MoS

Abstract

The molybdenum−sulfur bond plays an important role in many processes such as nitrogen-fixation, and it is found as a building block in layered materials such as MoS 2 , known for its various shapes and morphologies. Here, we present an accurate theoretical and experimental investigation of the chemical bonding and the electronic structure of 20 lowlying states of the MoS molecule. Multireference and coupled cluster methodologies, namely, MRCISD, MRCISD + Q, RCCSD(T), and RCCSD[T], were employed in conjunction with basis sets up to aug-cc-pwCV5Z-PP/aug-cc-pwCV5Z for the study of these states. We note the significance of including the inner 4s 2 4p 6 electrons of Mo and 2s 2 2p 6 of S in the correlated space to obtain accurate results. Experimentally, the predissociation threshold of MoS was measured using resonant two-photon ionization spectroscopy, allowing for a precise measurement of the bond dissociation energy. Our extrapolated computational D 0 value for the ground state is 3.936 eV, in excellent agreement with our experimental measurement of 3.932 ± 0.004 eV. The largest calculated adiabatic D 0 (5.74 eV) and the largest dipole moment (6.50 D) were found for the 5 Σ + state, where a triple bond is formed. Finally, the connection of the chemical bonding of the isolated MoS species to the relevant solid, MoS 2 , is emphasized. The low-lying septet states of the diatomic molecule are involved in the material as a building block, explaining the stability and the variety of the shapes and morphologies of the material.

Electronic Structure of the Low‐Lying States of the Triatomic MoS2 Molecule: The Building Block of 2D MoS2

“…The MoS( X 5 Π) D e value was calculated recently by our group at 92.01 kcal/mol (complete basis set limit of the C‐RCCSD[T]/aug‐cc‐pwCVxZ(−PP) Mo method, where the correlation of the core orbitals 4s4p of Mo and 2s2p of S have also been calculated) [20] . This value is in excellent agreement with our experimental value; [20] i. e., the D 0 calculated (experimental) values are 91.48 (90.67±0.09) kcal/mol. While, for the S 2 ($${{{\rm X}{}^{3}{\rm \Sigma }}_{{\rm g}}^{-}}$$ ) molecule, the CCSD(T)/wCV5Z [38] calculated (experimental) [39] dissociation energy is 102.5(102.9) kcal/mol.…”

“…However, in the bent septet states, single bonds are formed, with bond distance that ranges from 2.39 to 2.47, i. e., the same Mo−S bond distances with the calculated values in the 2D MoS 2 , see above. Note that the Mo−S distances in various polymorphs of Molybdenum sulfide are similar, i. e., 2.38–2.59 Å, [20,56] while in complexes and enzymes are about 2.35 Å [57] . For instance, in nitrogenase, which is a complex enzyme that catalyzes the formation of ammonia, the Mo−S bond distances ranges from 2.31 to 2.35 Å [61] .…”

“…Furthermore, it is worth noting that the septet states of the diatomic MoS, which present half or a single bonds, have bond distances that range from 2.36 to 2.52 Å. [20] The lowest septet state, 7 Π, has a dissociation energy of 2.66 eV, only 0.3 eV larger than the formation of the S vacancy of solid MoS 2 , 2.35 eV in S-rich conditions. [55] The calculated septet states of MoS 2 lie close in energy, i. e., the bent septet states differ in energy less than 10 kcal/mol, and as a result, all can be involved in the 2D material.…”

“…[19] Recently, we studied the diatomic MoS molecule both theoretically and experimentally, and emphasis was given to the formation of molybdenum-sulfur bond explaining the stability and the variety of the shapes and morphologies of the material. [20] As a continuation of this research, here we study the triatomic MoS 2 , which is the exact building block unit of the MoS 2 2D layers. In the present work, the ground and fifteen low-lying excited states of MoS 2 are studied via accurate multi reference configuration interaction methodologies.…”

CrN, CuB, and AuB: A Tale of Two Dissociation Limits

“…However, we argue that other states arising from the same limit will be barrier-free and that coupling to these states allows predissociation to occur when the excited SAL is reached. Moving forward, studying additional metal-p-block molecules where the metals have ground S terms (L = 0) is of interest to clarify when predissociation occurs to the ground SAL (as occurs in CrO, MoN, MoO, MoS, EuO, EuS, EuSe, and YbO) and when predissociation fails to occur at the ground SAL but can be observed at an excited SAL (as happens in CrN, CuB, AuB, and AlCr).…”