Enantiopure Tetranuclear Iron(III) Complexes Using Chiral Reduced Schiff Base Ligands: Synthesis, Structure, Spectroscopy, Magnetic Properties, and DFT Studies

摘要

Four new tetranuclear iron(III) complexes of formula E{Fe(L)_2}_3Fe], 1-4, have been prepared by reacting [Fe(ClO_4)_3]_¤6H_2O with H_2L in methanol. Here, L~(2-) is the deprotonated form of N-(2-hyrdoxybenzyl)-L-valinol (H_2L~1), N-(2-hyrdoxybenzyl)-L-leucinol (H_2L~2), N-(5-chloro-2-hyrdoxybenzyl)-L-leucinol (H_2L~3), and N-(2-hyrdoxyben_zyl)-L-phenylalaninol (H_2L~4). The complexes are prepared in an enantiomeric pure form. The complexes have been characterized with the help of IR, UV_vis, circular dichroism (CD), ~1H, and elemental analyses. The complex [{Fe(L~2)_2}_3Fe] _ CH_3OH _ 2H_2O, 2- CH_3OH _ 2H_2O, crystallizes in enantiomeric pure form containing a propeller-like Fe_40_6 core. ~1H and CD spectral studies of the four species are consistent with the structural similarities of the complexes in solution. Variable-temperature magnetic susceptibility of one case shows an intramolecular antiferro_magnetic coupling between the Fe(III) ions. Magnetic measurements are in accord with the S= 5 ground state and suggest single molecular magnet behavior. The magnetic exchange coupling constant between the iron centers within the molecule is interpreted using broken-symmetry density functional theory calculation.