Assignment of the Photoelectron Spectra of FeS₃^– by Density Functional Theory, CASPT2, and RCCSD(T) Calculations

Abstract

The geometric structures of FeS(3) and FeS(3)(-) with spin multiplicities ranging from singlet to octet were optimized at the B3LYP level, allowing two low-lying conformations for these clusters to be identified. The planar D(3h) conformation contains three S(2-) atomic ligands (S(3)Fe(0/-)), whereas the C(2v) structure contains, in addition to an atomic S(2-) ligand, also a S(2)(2-) ligand that is side-on-bound to the iron cation: an η(2)-S(2)FeS conformation. Subsequently, energy differences between the various states of these conformations were estimated by carrying out geometry optimizations at the multireference CASPT2 level. Several competing structures for the ground state of the anionic cluster were recognized at this level. Relative stabilities were also estimated by performing single-point RCSSD(T) calculations on the B3LYP geometries. The ground state of the neutral complex was unambiguously found to be (5)B(2). The ground state of the anion is considerably less certain. The 1(4)B(2), 2(4)B(2), (4)B(1), and (6)A(1) states were all found as low-lying η(2)-S(2)FeS(-) states. Also, (4)B(2) of S(3)Fe(-) has a comparable CASPT2 energy. In contrast, B3LYP and RCCSD(T) mutually agree that the S(3)Fe(-) state is at a much higher energy. Energetically, the bands of the photoelectron spectra of FeS(3)(-) are reproduced at the CASPT2 level as ionizations from either the (4)B(2) or (6)A(1) state of η(2)-S(2)FeS. However, the Franck-Condon factors obtained from a harmonic vibrational analysis at the B3LYP level show that only the (4)B(2)-to-(5)B(2) ionization, which preserves the η(2)-S(2)Fe-S conformation, provides the best vibrational progression match with the X band of the experimental photoelectron spectra.

Spin State Energetics of VGen−/0 (n = 5–7) Clusters and New Assignments of the Anion Photoelectron Spectra

“…This approach results in an active space of 14 or 13 electrons in 14 orbitals for VGe 5 −/0 and VGe 6 −/0 clusters, and of 12 or 11 electrons in 14 orbitals for VGe 7 −/0 clusters. The active spaces of 14 orbitals have been proven to sufficient to investigate the geometrical and electronic structures of transition metal‐containing clusters …”

Geometrical and Electronic Structures of MnS3–/0 Clusters from Computational Chemistry and Photoelectron Spectroscopy

“…For the FeS 3 − cluster, the computational results show that the most stable isomer is not the D 3h FeS 3 − isomer but the η 2 -(S 2 )FeS − isomer which contains a side-on S 2 and an atomic S ligand bound to Fe. 4 Although the D 3h MnS 3 − was calculated to be the most stable isomer of MnS 3 − cluster by the BLYP functional in the previous work, the relative stability of η 2 -(S 2 )MnS − isomer as compared to D 3h MnS 3 − was not reported. Therefore, quantum chemical calculations should be performed for η 2 -(S 2 )MnS − isomer in order to obtain the relative stability of this isomer.…”

Computational Investigation of the Geometrical and Electronic Structures of VGen–/0 (n = 1–4) Clusters by Density Functional Theory and Multiconfigurational CASSCF/CASPT2 Method

“…In such cases, the multiconfigurational CASSCF/CASPT2 method needs to be employed. With the ability to calculate the energies of all of the important ground and excited states with high accuracy, CASSCF/CASPT2 has been known as a sufficient method to investigate the low-lying states of transition metal-containing compounds. − Also, the electron detachment energies of the anionic clusters as computed with the CASPT2 method are usually in good agreement with the experimental values as observed in the photoelectron spectra. − ,− To the best of our knowledge, the multiconfigurational CASSCF/CASPT2 method has not been employed to study the geometrical and electronic structures of vanadium-doped germanium clusters.…”