Mössbauer, Electron Paramagnetic Resonance, and Crystallographic Characterization of a High-Spin Fe(I) Diketiminate Complex with Orbital Degeneracy
Citations Over TimeTop 10% of 2005 papers
Abstract
The synthesis and X-ray structure of the low-coordinate, high-spin Fe(I) compound LFe(HCCPh) (L = HC(C[tBu]N[2,6-diisopropylphenyl])2]-), 1, are reported. Low-temperature Mössbauer and electron paramagnetic resonance (EPR) spectroscopies reveal that the electronic ground state is a Kramers doublet with uniaxial magnetic properties (effective g values g(x) = 8.9, 0 < g(y), g(z) < 0.3) that is well isolated from the excited states. The observation of a large and positive magnetic hyperfine field, B(int) = +68.8(3) T, demonstrates that the orbital angular moment is essentially unquenched along one spatial direction. Relaxation rates obtained from variable-temperature Mössbauer spectra were fit to an Orbach process, yielding delta = 130-190 cm(-1) for the energy gap ("zero-field splitting") between the two Kramers doublets of the S = 3/2 multiplet. Density functional theory (DFT) and time-dependent DFT calculations give insight into the electronic structures of the ground and excited states. The oxidation state of the iron and the bond order of the phenylacetylene ligand in complex 1 are analyzed using DFT, showing a substantial back-bonding interaction. Spin-orbit coupling acting in the subspace of quasi-degenerate z2 and yz orbitals provides a consistent description of both the zero-field splitting and magnetic hyperfine parameters that fits the EPR and Mössbauer data for 1. Interestingly, the spin-orbit coupling involves the same two orbitals (z2, yz) as in the analogous three-coordinate Fe(II) compounds, because back-bonding significantly lowers the energy of the xy orbital, making it the lowest doubly occupied d orbital. Despite the different oxidation state and different number of atoms in the first coordination sphere, the electronic structure of LFe(I)(HCCPh) can be interpreted similarly to that of three-coordinate Fe(II) diketiminate complexes, but with a substantial effect of back-bonding. To our knowledge, this is the first detailed Mössbauer and EPR study of a structurally characterized high-spin Fe(I) complex.
Related Papers
- → Theoretical studies of the electronic structure of copper in tetrahedral and triangular coordination with sulfur(1978)26 cited
- → The stereochemistry of metal complexes as an indication of f-orbital participation in the metal–ligand bonding(1967)18 cited
- → The use of population localised orbitals to interpret molecular orbital calculations(1979)35 cited
- → Some new theorems and methods for establishing the relationship between the symmetry of a molecular orbital and its energy(1978)3 cited
- → Theoretical study of spin-singlet contributions to zero-field splitting of a 3d6ion in a trigonal ligand field and applications to Fe2+in FeSiF6· 6H2O and FeCO3(2008)1 cited