Structures and Magnetic Properties of Some Fe(III) Complexes with Hexadentate Ligands: In Connection with Spin-Crossover Behavior

Article abstract of DOI:10.1246/bcsj.70.3001

Several iron(III) complexes with the different hexadentate Schiff-base ligands of N₄O₂ donor sets were synthesized; these are 1 : 2 condensation products of linear tetramines (3,3,3-, 3,2,3-, 2,3,2- or 2,2,2-tetramine) and salicylaldehyde, acetophenone or benzophenone derivatives. Their crystal structures, Moessbauer spectra, magnetic susceptibilities, electronic spectra and cyclic voltammetry of the complexes were examined. The X-ray structures of the single crystals of [Fe(3,2, 3-sal₂tet)]NO₃ (1), [Fe(3,2,3-sal₂tet)]BPh4 (2), [Fe(3,2,3-mpk₂tet)]PF₆ (3), [Fe(2,3,2-sal₂tet)]ClO₄ (4), [Fe(2,3,2-3MeO-sal₂tet)]ClO₄ (5), [Fe(2,3,2-mpk₂tet)]ClO₄ (6), [Fe(2,3,2-bpk₂tet)]ClO₄ (7), and [Fe(2,2,2-bpk₂tet)]ClO₄·EtOH (8) were determined. Crystal data for (1): C₂₂H₂₈N₅O₅Fe, space group P2₁/c, Z = 4, a = 7.607(1), b = 16.063(1), c = 19.063(1) A, β = 91.00(2)°, V = 2329(3) A³, R = 5.8%, R_w = 4.2%, 4605 reflections. Crystal data for (2): C₄₆H₄₈N₄O₂BFe, space group P2₁/n, Z = 4, a = 14.390(6), b = 20.617(8), c = 14.754(5) A, β = 115.85(2)°, V = 3939(2) A³, R = 6.3%, R_w = 6.7%, 7458 reflections. Crystal data for (3): C₂₄H₃₂N₄O₂PF₆Fe, space group P2₁/c, Z = 4, a = 9.37(6), b = 24.15(7), c = 12.85(3) A, β = 97.7(3)°, V = 2880(17) A³, R = 10.9%, R_w = 13.6%, 5569 reflections. Crystal data for (4): C₂₁H₂₆N₄O₆ClFe, space group Pbcn, Z = 4, a = 11.041(2), b = 17.251(2), c = 11.722(2) A, V = 2232(1) A³, R = 3.9%, R_w = 2.8%, 2258 reflections. Crystal data for (5): C₂₃H₃₀N₄O₈ClFe, space group Pccn, Z = 8, a = 14.567(1), b = 22.288(1), c = 15.477(1) A, V = 5025(4) A³, R = 6.3%, R_w = 6.2%, 4956 reflections. Crystal data for (6): C₂₃H₃₀N₄O₆ClFe, space group Pbca, Z = 8, a = 28.249(4), b = 13.989(4), c = 13.174(4) A, V = 5205(1) A³, R = 8.2%, R_w = 8.4%, 5148 reflections. Crystal data for (7): C₃₃H₃₄N₄O₆ClFe, space group P1, Z = 2, a = 10.241(3), b = 17.373(1), c = 9.692(7) A, α = 105.95(6)° β = 91.61(4)°, γ = 93.83(4)°, V = 1652(1) A³, R = 7.1%, R_w = 7.6%, 6179 reflections. Crystal data for (8): C₃₄H₃₈N₄O₇ClFe, space group P2₁/c, Z = 4, a = 14.553(4), b = 14.079(4), c = 16.959(6) A, β = 94.92(3)°, V = 3461(1) A³, R = 8.4%, R_w = 7.7%, 6651 reflections. The moieties of the iron atoms of (1), (2), and (3) with 3,2,3-tetramine, and (7) with 2,3,2-tetramine were pseudo octahedral with trans-FeN₄O₂ geometry. Those of (4), (5), and (6) with 2,3,2-tetramine, and (8) with 2,2, 2-tetramine were cis-FeN₄O₂ geometry. The iron(III) complexes (1), (2), (3), and (7) were in the low-spin state, and the iron(III) complexes (4), (5), (6), and (8) were in the high-spin state. In the electronic spectra, the wave lengths of the LMCT bands for the low-spin complexes were longer than those for the high-spin complexes. The values of redox potentials for the low-spin states were suggested to be 0.12 V more negative than those for the high-spin states.