New poly-iron(II) complexes of N4O dinucleating Schiff bases and pseudohalides:: Syntheses, structures, and magnetic and Mossbauer properties

Six dinuclear ferrous complexes including [Fe2(acpypentO)(O 2CMe)(NCS)2] (1), [Fe2(acpypentO)(O 2CMe)(NCSe)2] (2), [Fe2(acpypentO)(NCO) 3] (3), ([Fe2(acpybutO)(O2CMe)(NCS) 2] (5), [Fe2(acpybutO)(O2CMe)(NCO) 2] (6), and [Fe2(acpybutO)(O2CMe)(N 3)2] (7), one tetranuclear (bis-dinuclear) ferrous compound, [Fe4(acpypentO)2(N3)6] (4), and one mononuclear ferrous compound, [Fe(acpybutOH)(NCS)2] (8), have been prepared, and their structures and magnetic and Mössbauer properties have been studied (acpybutOH = 1,4-bis{[2-pyridyl(1-ethyl]imino)}butane-2-ol and acpypentOH = 1,5-bis{[2-pyridyl(1-ethyl]imino)}pentane-3-ol). The X-ray diffraction analyses yielded the following results: 1 (C23H26Fe 2N6O3S2, monoclinic, P2 1/n, a = 8.0380(7) Å, b = 12.4495(8) Å, c = 27.358(2) Å, β = 92.180(10)°, V = 2735.7(4) Å3, Z = 4) is a dinuclear species in which the unequivalent high-spin (HS) FeII sites are bridged by the alkoxo oxygen atom of the symmetrical acpypentO - Schiff base and one syn-syn acetato anion; 3 (C22H 23Fe2N7O4, triclinic, P1̄, a = 8.4152(10) Å, b = 9.1350(10) Å, c = 17.666(2) Å, α = 97.486(14)°, β = 100.026(14)°, γ = 113.510(13)°, V = 1195.9(2) Å3, Z = 2) is a dinuclear species in which the unequivalent HS FeII sites are bridged by the alkoxo oxygen atom of the symmetrical acpypentO- Schiff base and one end-on NCO anion; 4-MeOH (C39H50Fe4N26O3, triclinic, P1̄, a = 9.1246(11) Å, b = 10.2466(11) Å, c = 14.928(2) Å, α = 91.529(15)°, β = 101.078(16)°, γ = 106.341(14)°, V = 1309.6(3) Å3, Z = 1) is a bis-dinuclear species in which the unequivalent HS FeII sites are bridged by the alkoxo oxygen atom of the symmetrical acpypentO- Schiff base and one end-on N3- anion, and the symmetry related FeII sites are bridged by two end-on N3 - anions; 8-MeOH (C21H26FeN6O 2S2, triclinic, P1̄, a = 8.7674(9) Å, b = 12.0938(13) Å, c = 12.2634(14) Å, α = 106.685(14)°, β = 93.689(14)°, γ = 108.508(13)°, V = 1163.7(2) Å 3, Z = 2) is a mononuclear species in which the octahedral low-spin (LS) FeII site is in an N6 environment provided by the four N atoms of the protonated asymmetrical acpybutOH Schiff base and two thiocyanato anions. The Mössbauer spectra of all dinuclear species (1-3 and 5-7), and of the bis-dinuclear compound 4, evidence two distinct HS Fe II sites while the Mössbauer spectra of the mononuclear compound 8 evidence a LS FeII site over the 80-300 K temperature range. The temperature dependence of the magnetic susceptibility was fitted with J = -13.7 cm-1, D = -1.8 cm-1, and g = 2.096 for 1; J = 3.0 cm-1, D1 = 1.6 cm-1, E1 = -0.35 cm-1 (λ1 = 0.22), D2 = -12.2 cm-1, E2 = 1.1 cm-1 (λ2 = 0.09), and g = 2.136 for 3; and J1 = -0.09 cm-1, J 2 = 15.9 cm-1, D1 = 5.7 cm-1, D 2 = 12.1 cm-1, and g = 1.915 for 4. The nature of the ground state in 3 and 4 was confirmed by simulation of the magnetization curves at 2 and 5 K. The intradinuclear interaction through the central O alkoxo of the acpypentO- ligand and one pseudohalide bridges is ferromagnetic in 3 (end-on cyanato) while it is very weakly antiferromagnetic in 4 (end-on azido). The interdinuclear interaction through two end-on azido bridges (4) is ferromagnetic as expected. In agreement with the symmetry of the two iron sites of complexes 3 and 4, the fits show that D2 (tetragonal pyramid) is larger than D1 (distorted trigonal bipyramid (3) or distorted octahedron (4)).