Experimental and computational study of the new gaseous molecules OMnF and OMnF2

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

On reacting laser-ablated manganese or iron difluorides with O₂ or O₃ during codeposition in solid neon or argon, infrared absorptions of several new metal oxo-fluoride molecules, including OMF₂, (η¹-O₂)MF₂, (η²-O₃)MF₂, (η¹-O₂)₂MF₂ (M = Mn and Fe), and O₂MnF, have been observed. Quantum chemical density functional and multiconfiguration wavefunction calculations have been applied to characterize these new products by their geometric and electronic structures, vibrations, charges, and bonding. The assignment of the main vibrational absorptions as dominant symmetric or antisymmetric M-F or M-O stretching modes is confirmed by oxygen isotopic shifts and quantum chemical calculations of frequencies and thermal stabilities. The tendency of Fe to form polyoxygen complexes in lower oxidation states than the preceding element Mn is affirmed experimentally and supported theoretically. The M-F stretching frequencies of the isolated metal oxo-fluorides may provide a scale for the local charge on the MF₂ sites in active energy conversion systems. The study of these species provides insights for understanding the trend of oxidation state changes across the transition-metal series.

First principles study of the diatomic charged fluorides MF±, M=Sc, Ti, V, Cr, and Mn

Employing multireference configuration interaction and coupled-cluster methods in conjunction with quantitative basis sets, we have explored the electronic structure of the charged diatomic fluorides MF(+/-), where M=Sc, Ti, V, Cr, and Mn. In addition, and in order to complete our recently published work on the neutral diatomic fluorides MF, M=Ti-Mn, we have also examined the ground (X (1)Sigma(+)) and the first excited state (alpha (3)Delta) of neutral ScF. For the entire anionic MF(-) series and the cations ScF(+), VF(+), and MnF(+), no experimental or theoretical results of any kind have been reported so far in the literature. For the charged MF(+/-) sequence we have investigated a total of 43=29(MF(+))+14(MF(-)) states, reporting potential energy curves, energetics, and common spectroscopic parameters. Two are the most interesting conclusions of the present work. (a) The Coulombic binding character of MF(+) cations, i.e., the conformity of their equilibrium description to M(2+)F(-) and (b) the atypical bonding of the MF(-) anions and their surprisingly high dissociation energies (up to 85 kcal/mol for the X (2)Delta state of ScF(-)). Considering the complexities of these chemically "simple" systems, our results on ScF, TiF(+), and CrF(+) are in very good agreement with the limited experimental findings.

High-Level ab Initio Thermochemical Data for Halides of Chromium, Manganese, and Iron

The thermochemistry of the transition-metal fluorides and chlorides MF(n)() and MCl(n)() (M = Cr, Mn, Fe; n = 1, 2) has been characterized by high-level ab initio electronic structure methods. Geometries and harmonic vibrational frequencies were computed at the B3LYP level of theory using triple-zeta basis sets including diffuse and polarization functions. Heats of formation were computed from isogyric reaction energies at the CCSD(T) level using high-quality basis sets, including corrections for core-valence correlation and scalar relativistic effects. To investigate the possible linearity of the ground states of CrCl(2) and CrF(2), we performed geometry optimizations for these species at the CCSD(T) level using large basis sets. In both cases, a bent ((5)B(2)) minimum structure was located, but the bent structure is only slightly below the linear form, which was found to be a transition state. For all of the investigated halides, polynomial fits were carried out for the heat capacity and the standard enthalpy and entropy in the 300-3000 K temperature range.

Ab initio investigation of the ground and low-lying states of the diatomic fluorides TiF, VF, CrF, and MnF

The electronic structure of the ground and low-lying states of the diatomic fluorides TiF, VF, CrF, and MnF was examined by multireference and coupled cluster methods in conjunction with extended basis sets. For a total of 34 states we report binding energies, spectroscopic constants, dipole moments, separation energies, and charge distributions. In addition, for all states we have constructed full potential curves. The suggested ground state binding energies of TiF(X (4)Phi), VF(X (5)Pi), CrF(X (6)Sigma(+)), and MnF(X (7)Sigma(+)) are 135, 130, 110, and 108 kcal/mol, respectively, with first excited states A (4)Sigma(-), A (5)Delta, A (6)Pi, and a (5)Sigma(+) about 2, 3, 23, and 19 kcal/mol higher. In essence all our numerical findings are in harmony with experimental results. For all molecules and states studied it is clear that the in situ metal atom (M) shows highly ionic character, therefore the binding is described realistically by M(+)F(-).