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 ...

Complex [FeO(OCPh)(py)]ClO·py (1) crystallizes in the hexagonal P6/m space group, and its cation exhibits a crystallographically imposed D symmetry due to a C axis passing through the oxide of its {FeO} core. Single-crystal unit-cell studies carried out with synchrotron radiation confirmed that this symmetry is retained down to 4.5 K; a full crystal structure determination carried out at 90 K resolved the previously reported disorder of the perchlorate anion. Magnetic susceptibility and electron paramagnetic resonance (EPR) data for complex 1 were interpreted with a model considering the retention of the threefold crystallographic symmetry while predicting a lowering of the magnetic symmetry. This model considered the effects of atomic vibrations of the central oxide on the magnetic properties of the complex by incorporating these movements into the spin Hamiltonian through angular overlap considerations of the atomic orbitals; no ad hoc magnetic Jahn-Teller effect was considered. The derived magnetostructural correlations achieved an improvement in the interpretation of the magnetic susceptibility data using the same number of free variables. They also improved the simulations of the EPR data, which exhibit a complicated set of at least five axial resonances; improved simulations were achieved using only two spectral components. Due to the thermal effects on the oxide vibrations, the model predicts a temperature dependence of the magnetic coupling J, which should not be viewed as a constant but as a variable.

A new asymmetrically coordinated bis-trinuclear iron(III) cluster containing a {Fe 3 O} 7+ core has been synthesized and structurally, magnetically, and spectroscopically characterized. [Fe 6 Na 2 O 2 (O 2 CPh) 10 (pic) 4 (EtOH) 4 (H 2 O) 2 ](ClO 4 ) 2 ‚ 2ΕtOH (1‚2ΕtOH) crystallizes in the P1 h space group and consists of two symmetry-related {Fe 3 O} 7+ subunits linked by two Na + cations. Inside each {Fe 3 O} 7+ subunit, the iron(III) ions are antiferromagnetically coupled, and their magnetic exchange is best described by an isosceles triangle model with two equal (J) and one different (J ′) coupling constants. On the basis of the H ) −2ΣJ ij S i S j spin Hamiltonian formalism, the two best fits to the data yield solutions J ) −27.4 cm -1 , J ′ ) −20.9 cm -1 and J ) −22.7 cm -1 , J ′ ) −31.6 cm -1 . The ground state of the cluster is S ) 1 / 2 . X-band electron paramagnetic resonance (EPR) spectroscopy at liquid-helium temperature reveals a signal comprising a sharp peak at g ∼ 2 and a broad tail at higher magnetic fields consistent with the S ) 1 / 2 character of the ground state. Variable-temperature zero-field and magnetically perturbed Mo ¨ssbauer spectra at liquid-helium temperatures are consistent with three antiferromagnetically coupled high-spin ferric ions in agreement with the magnetic susceptibility and EPR results. The EPR and Mo ¨ssbauer spectra are interpreted by assuming the presence of an antisymmetric exchange interaction with |d| ∼ 2−4 cm -1 and a distribution of exchange constants J ij .