High-spin and Low-spin Α-picolylamine Iron(II) Complexes
Effect of ligand reversal on spin state
The magnetic properties and single crystal structures of the α-picolylamine (α-P) complexes, [Fe(α-P)3]Cl2·2H2O and [Fe(α-P)3]Cl2·CH3OH, have been studied in order to discover the relationship between spin state and molecular structure. The dihydrate solvate is low spin at room temperature and below, while the methanol solvate is high spin at room temperature, undergoing a transition to low spin in the region 100-200 K. The room temperature molecular structures of the two complexes exhibit some major differences. The hydrate complex has all three ligands related approximately chirally so that the [Fe-(α-P)3]2+ ion has approximate threefold symmetry. However, the methanol solvate has one of the ligands coordinated with both of its donor atoms reversed. This difference is attributed to hydrogen bonding which occurs only in the dihydrate. The pseudo-threefold axis places all three amine nitrogen atoms on one side of the ion, thereby facilitating hydrogen bonding between the amine nitrogens and the water molecules. This hydrogen bonding is absent in the methanol solvate, and the structure that it exhibits is presumably the more stable one in the absence of hydrogen bonding. The average metal-ligand bond distance, 〈Fe-N〉, is 0.192 Å larger in the high-spin methanol solvate than in the low-spin complex. This is the largest value ever observed for the bond length difference between high-spin and low-spin states. Crystal data for [Fe(α-P)3]Cl2·2H2O follow: space group P1, Z = 2, a = 10.142 (2) Å, b = 10.651 (4) Å, c = 11.351 (2) Å, α = 113.89 (2)°, β = 98.50 (2)°, γ = 93.97 (2)°, V = 1097 Å3, R = 3.3% for 3180 reflections. Crystal data for [Fe(α-P)3]Cl2·CH3OH follow: space group Pbca, Z = 8, a = 22.428 (6) Å, b = 11.524 (2) Å, c = 18.906 (5) Å, V = 4887 Å3, R = 4.1% for 1712 reflections. © 1978 American Chemical Society.
A. M. Greenaway and E. Sinn, "High-spin and Low-spin Α-picolylamine Iron(II) Complexes," Journal of the American Chemical Society, American Chemical Society (ACS), Jan 1978.
The definitive version is available at https://doi.org/10.1021/ja00494a009
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© 1978 American Chemical Society (ACS), All rights reserved.