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

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 C₂ 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.