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 ...

A Diferrous Single‐Molecule Magnet

“…In the temperature range 10-78 K, there is no significant variation of the doublets: the two sites exhibit almost temperature-independent isomer shifts and quadrupole splittings. For temperatures below 10 K, the spectra exhibit line-broadening and a spectrum with magnetic features is observed at 4.2 K. These spectra look slightly different from those recorded previously [13] essentially because of a remarkable sensitivity related to a strong dependence of the relaxation times on temperature below 7 K. From DC magnetic susceptibility measurements, no evidence for long-range effects were observed, which suggests that the magnetically split spectrum at 4.2 K is due to slow paramagnetic relaxation. The Mössbauer spectra are in line with the magnetic susceptibility measurements, which indicate ferromagnetic coupling between the ferrous ions.…”

“…At 78 K, the two ferrous sites are characterized by δ 1 = 1.01 mm s -1 , ∆E Q1 = 2.27 mm s -1 and δ 2 = 1.01 mm s -1 , ∆E Q2 = 3.38 mm s -1 . [13] The temperature dependence of the isomer shifts above 78 K is attributed to the second-order Doppler effect whereas the dependence of the quadrupole splitting values is typical for high-spin ferrous ions.…”

“…Recently, we reported the synthesis and physical characterization of a series of polynuclear Fe II complexes including the dinuclear species [Fe 2 (acpypentO)(NCO) 3 ] (1), [13] where acpypentO -is the anion of 1,5-bis[2-pyridyl(1-ethylimino)]pentane-3-ol ( Figure 1). This complex was found to contain two pentacoordinate Fe II ions bridged by one alkoxido oxygen belonging to the ligand, and one end-on cyanato anion.…”

Antiferromagnetic Co–Gd Interactions in a Tetranuclear [CoGd]2 Complex with Low‐Spin Square‐Planar Co Ions – Role of the Singly Occupied 3d Co Magnetic Orbital

“…In view of the structural data, the magnetic susceptibility has been computed by exact calculation of the energy levels associated with the spin Hamiltonian H = -J CoGd (S Co1 ·S Gd1 + S Co2 ·S Gd2 ) -j CoGd (S Co1 ·S Gd2 + S Co2 ·S Gd1 ) through diagonalization of the full energy matrix. [13] The best fit yields the following data, J CoGd = -1.0 cm -1 , j CoGd = -0.10 cm -1 , g = 2.04, with an R factor equal to 1.0 ϫ 10…”

Tetra‐ and Decanuclear Iron(II) Complexes of Thiacalixarene Macrocycles: Synthesis, Structure, Mössbauer Spectroscopy and Magnetic Properties

“…The II -O(phenoxy) distances. [47][48][49][50][51][52][53][54] The Fe II -S bond lengths are longer than the few previously reported for thioether complexes of high-spin iron(ii) (2.20-2.29 Å). [55] This should be due to the rigidity of the macrocycle, which does not allow the sulfur atoms to come closer to the iron(ii) ions.…”