ESR spectra of the MnO, MnO2, MnO3, and MnO4 molecules at 4 °K

Abstract

The molecules MnO, MnO2, MnO3, and MnO4 have been prepared by the vaporization and reaction of manganese atoms with O2, N2O, or O3 and isolated in various inert-gas matrices at 4 °K. ESR has been used to determine magnetic parameters which are interpreted in terms of molecular geometry and electronic structure. MnO is confirmed to have a σπ2δ2, 6Σ+ ground state with g⊥=1.990(7) (assuming g∥=ge) and a zero-field splitting in accord with the gas phase value ‖D‖=1.32 cm−1. Hyperfine splittings due to the 55Mn (I=5/2) nucleus are ‖A∥‖=176(8) and ‖A⊥‖=440(11) MHz. MnO2 is a linear 4Σ− molecule with probable configuration σδ2, ‖D‖=1.13 cm−1 (assuming g∥=g⊥=2.0023), ‖A∥‖=353(11), ‖A⊥‖=731(11) MHz. MnO3 exhibits very large hf splittings ‖A∥‖=1772(3) and ‖A⊥‖=1532(3) MHz indicative of a sdz2 hybrid 2A1 ground state of D3h symmetry. The spectrum of MnO4 is consistent with a C3v molecule distorted from a 2T1 electronic state in tetrahedral symmetry by a static Jahn–Teller effect. g and A tensors are slightly anisotropic: g∥=2.0108(8), g⊥=2.0097(8), ‖A∥‖=252(3), ‖A⊥‖=196(3) MHz. The electron hole is almost entirely in an oxygen π-bonded orbital with one oxygen atom displaced along its Mn–O bond axis.

Microwave spectrum of the MnO radical in the X 6Σ+ state

“…[4][5][6][7][8] The rotational, centrifugal distortion, spin-spin coupling, spin-rotation coupling, and the two main hyperfine coupling constants agree well with those obtained by intermodulated fluorescence spectroscopy. 8 Eight minor molecular constants: three hyperfine ͓C I (Mn), b S (Mn), and eQq(Mn)͔; two higher-order fine structure ͑␥ S and ⌰͒; and three centrifugal distortion ͑ D , ␥ D , and b FD ͒ were determined.…”

“…As Ferrante et al 5 discussed the dipolar hfs constant c of MnO is related to a sum of contributions from the 3d unpaired electrons in the 9, 4, and 1␦ orbitals: Using c 2 2 ϭ0.427, the angular expectation values for the 3d orbital, ͗3 cos 2 Ϫ1͘ϭ4/7 for 3d, 2/7 for 3d, and Ϫ4/7 for 3d␦, and the radial expectation value for 3d, ͗1/r 3 ͘ 3d ϭ4.167 a.u. Ϫ3 , 27 c is calculated to be Ϫ54.0 MHz, which may be compared with the observed value of Ϫ48.168 MHz.…”

A Critical Validation of Density Functional and Coupled-Cluster Approaches for the Calculation of EPR Hyperfine Coupling Constants in Transition Metal Complexes

“…The trigonal planar structures are consistent with hyperfine data [44][45][46][47] and IR spectra. 48 58 converged to a regular square pyramid (C 4V ), in agreement with the observed hyperfine structure.…”

Basis set error estimation for DFT calculations of electronic g‐tensors for transition metal complexes

“…For the latter, it should be noted that the majority of experimental values are indeed obtained in a medium, either solution, a frozen matrix or a crystal . Only one experimental g‐tensor component is reported in gas phase . Further studies of such effects could favorably be conducted using the locally dense basis set approach as advocated above.…”