Infrared Spectroscopic and Theoretical Studies of the 3d Transition Metal Oxyfluoride Molecules

Abstract

A collection of 3d transition metal (V, Mn, Fe, Co, and Ni) oxyfluorides were prepared via the reactions of laser-ablated metal atoms and OF2 in an argon matrix, and the products were identified by infrared spectroscopy together with 18OF2 substitution. OMF2 is the major product from the reactions of metal atoms and OF2. The tetravalent metal center is coordinated to two fluorine atoms and one oxygen atom. Triatomic OMF molecules were observed in the reactions of V, Mn, Fe, and Co with OF2. In addition to OMF and OMF2, OMnF3 and OFeF3 were also formed presumably via the reactions of OMnF and OFeF with F2 resulting from photodecomposition of OF2. The seldom observed OF radical was produced in all of these experiments. Electronic structure calculations at the density functional theory and molecular orbital theory including electron correlation effects (CCSD­(T) and CASPT2) levels are used to aid in the assignment of the structures. For OMF (M = Sc–Mn), the structures are bent and those for M = Fe–Cu are linear. The OMF2 molecules are optimized to be C 2v structures. Both OMF and OMF2 have a high spin ground state, with the exception of OCoF2 in which the ground state quartet is the lower energy structure. The M–O stretching frequency is a sensitive measure of the computational method in terms of the bond angle, the coupling of the M–O and M–F stretches, and the amount of spin on the oxygen. A bonding analysis in terms of the CAS orbitals shows that a number of the structures have a multireference character after M = Cr. Oxidation states of the metal are given based on the CASPT2 results. Heats of formation for the OMF and OMF2 are reported.

Multireference Electron Correlation Methods: Journeys along Potential Energy Surfaces

“…Unlike most of the works that report CASPT2 geometry optimization that were focused on organic molecules, a series of papers by Andrews and coworkers [98][99][100][101][102][103][104] explored the electronic structure of small actinide and transition metal complexes in noble gas matrices. These studies demonstrated the importance and applicability of CASPT2 for geometry optimization and harmonic vibrational frequencies calculations, using numerical gradients and numerical Hessian calculations available in molcas.…”

“…30 The species that were studied include N≡UF 3 and P≡UF 3 ; 98 FB=ThF 2 ; 101 N≡U=N-H; 102 SUO and US 2 ; 103 halomethanes with laser-ablated nickel, palladium, and platinum; 99,100 and 3d transition metal oxyfluoride molecules. 104 The numerical gradient implementations of CASPT2 and XMCQDPT2 remain in widespread use for optimizing molecular structures. Notable examples include locating equilibrium geometries and conical intersections with MS-CASPT2 in 2011, 46 locating equilibrium geometries and conical intersection in acetophenone with XMCQDPT2 in 2013, 52 locating equilibrium geometries, conical intersections, transition state geometries, and reaction pathways of thymine with MS-CASPT2 in 2016, 60 locating equilibrium geometries of various RPSB models in 2017, 65 generating a benchmark set of excited-state geometries of organic molecules with MS-CASPT2 in 2017, 67 and optimizing equilibrium structures and crossing points in 2-selenouracil in 2019.…”

Metal Oxo-Fluoride Molecules OnMF2 (M = Mn and Fe; n = 1–4) and O2MnF: Matrix Infrared Spectra and Quantum Chemistry

“…In our argon matrix isolation experiments, the absorptions of the OMnF 2 molecule were observed (Table 1) at 928.0 and 757.0 cm −1 , respectively, which have been reported with the same values for the reaction of Mn with OF 2 in solid argon. 13 The neon−argon matrix shifts of the stretching modes are smaller (8.3 cm −1 reduction) for the more covalent Mn−O bond and larger (12.8 cm −1 ) for the almost purely ionic Mn−F bond. Notably, these absorptions of OMnF 2 in solid argon are very different from some previously reported values.…”

“…In our argon matrix experiments, the absorptions of the OFeF 2 molecule were detected at 882.5 and 761.3 cm −1 , which are the same as the values observed in Fe atom reactions with OF 2 in solid argon. 13 The B3LYP DF calculations on the free molecules yielded the MO stretching wavenumbers +6.7% (M = Mn) and +4.4% (M = Fe) too high and the antisymmetric FMF modes −0.4% and −0.7%, respectively, too low (Table 2). Note that the vibrations dominated by ionic M−F interactions are rather accurately reproduced, while the modes dominated by the more covalent M−O interactions are slightly overestimated as usual.…”

“…The geometric parameters are close to earlier and more recent predictions. 13,38 While the M−F distance (around 1. The calculated frequencies of these species are listed in Table 2.…”