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

Abstract

Six dinuclear ferrous complexes including [Fe2(acpypentO)(O2CMe)(NCS)2] (1), [Fe2(acpypentO)(O2CMe)(NCSe)2] (2), [Fe2(acpypentO)(NCO)3] (3), ([Fe2(acpybutO)(O2CMe)(NCS)2] (5), [Fe2(acpybutO)(O2CMe)(NCO)2] (6), and [Fe2(acpybutO)(O2CMe)(N3)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 (C23H26Fe2N6O3S2, monoclinic, P2(1)/n, a = 8.0380(7) A, b = 12.4495(8) A, c = 27.358(2) A, beta = 92.180(10) degrees, V = 2735.7(4) A(3), Z = 4) is a dinuclear species in which the unequivalent high-spin (HS) Fe(II) sites are bridged by the alkoxo oxygen atom of the symmetrical acpypentO- Schiff base and one syn-syn acetato anion; 3 (C22H23Fe2N7O4, triclinic, Ponemacr;, a = 8.4152(10) A, b = 9.1350(10) A, c = 17.666(2) A, alpha = 97.486(14) degrees, beta = 100.026(14) degrees, gamma = 113.510(13) degrees, V = 1195.9(2) A3, Z = 2) is a dinuclear species in which the unequivalent HS Fe(II) sites are bridged by the alkoxo oxygen atom of the symmetrical acpypentO- Schiff base and one end-on NCO anion; 4-MeOH (C39H50Fe4N26O3, triclinic, Ponemacr;, a = 9.1246(11) A, b = 10.2466(11) A, c = 14.928(2) A, alpha = 91.529(15) degrees, beta = 101.078(16) degrees, gamma = 106.341(14) degrees, V = 1309.6(3) A3, Z = 1) is a bis-dinuclear species in which the unequivalent HS Fe(II) sites are bridged by the alkoxo oxygen atom of the symmetrical acpypentO- Schiff base and one end-on N(3)(-) anion, and the symmetry related Fe(II) sites are bridged by two end-on N3- anions; 8-MeOH (C21H26FeN6O2S2, triclinic, Ponemacr;, a = 8.7674(9) A, b = 12.0938(13) A, c = 12.2634(14) A, alpha = 106.685(14) degrees, beta = 93.689(14) degrees, gamma = 108.508(13) degrees, V = 1163.7(2) A3, Z = 2) is a mononuclear species in which the octahedral low-spin (LS) Fe(II) 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 Fe(II) 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), D(1) = 1.6 cm(-1), E(1) = -0.35 cm(-1) (lambda(1) = 0.22), D2 = - 12.2 cm(-1), E2 = 1.1 cm(-1) (lambda2 = 0.09), and g = 2.136 for 3; and J(1) = - 0.09 cm(-1), J(2) = 15.9 cm(-1), D(1) = 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)).