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Novel Rectangular [Fe44-OHO)(μ-OH)2]7+ versus “Butterfly” [Fe43-O)2]8+ Core Topology in the FeIII/RCO2-/phen Reaction Systems (R = Me, Ph; phen = 1,10-Phenanthroline):  Preparation and Properties of [Fe4(OHO)(OH)2(O2CMe)4(phen)4](ClO4)3, [Fe4O2(O2CPh)7(phen)2](ClO4), and [Fe4O2(O2CPh)8(phen)2]

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journal contribution
posted on 02.11.2002 by Athanassios K. Boudalis, Nikolia Lalioti, Georgios A. Spyroulias, Catherine P. Raptopoulou, Aris Terzis, Azzedine Bousseksou, Vassilis Tangoulis, Jean-Pierre Tuchagues, Spyros P. Perlepes
The preparations, X-ray structures, and detailed physical characterizations are presented for three new tetranuclear FeIII/RCO2-/phen complexes, where phen = 1,10-phenanthroline:  [Fe4(OHO)(OH)2(O2CMe)4(phen)4](ClO4)3·4.4MeCN·H2O (1·4.4MeCN·H2O); [Fe4O2(O2CPh)7(phen)2](ClO4)·2MeCN (2·2MeCN); [Fe4O2(O2CPh)8(phen)2]·2H2O (3·2H2O). Complex 1·4.4MeCN·H2O crystallizes in space group P21/n, with a = 18.162(9) Å, b = 39.016(19) Å, c = 13.054(7) Å, β = 104.29(2)°, Z = 4, and V = 8963.7 Å3. Complex 2·2MeCN crystallizes in space group P21/n, with a = 18.532(2) Å, b = 35.908(3) Å, c = 11.591(1) Å, β = 96.42(1)°, Z = 4, and V = 7665(1) Å3. Complex 3·2H2O crystallizes in space group I2/a, with a = 18.79(1) Å, b = 22.80(1) Å, c = 20.74(1) Å, β = 113.21(2)°, Z = 4, and V = 8166(1) Å3. The cation of 1 contains the novel [Fe44-OHO)(μ-OH)2]7+ core. The core structure of 2 and 3 consists of a tetranuclear bis(μ3-O) cluster disposed in a “butterfly” arrangement. Magnetic susceptibility data were collected on 13 in the 2−300 K range. For the rectangular complex 1, fitting the data to the appropriate theoretical χM vs T expression gave J1 = −75.4 cm-1, J2 = −21.4 cm-1, and g = 2.0(1), where J1 and J2 refer to the FeIIIO(O2CMe)2FeIII and FeIII(OH)FeIII pairwise exchange interactions, respectively. The S = 0 ground state of 1 was confirmed by 2 K magnetization data. The data for 2 and 3 reveal a diamagnetic ground state with antiferromagnetic exchange interactions among the four high-spin FeIII ions. The exchange coupling constant Jbb (“body−body” interaction) is indeterminate due to prevailing spin frustration, but the “wing−body” antiferromagnetic interaction (Jwb) was evaluated to be −77.6 and −65.7 cm-1 for 2 and 3, respectively, using the appropriate spin Hamiltonian approach. Mössbauer spectra of 13 are consistent with high-spin FeIII ions. The data indicated asymmetry of the Fe4 core of 1 at 80 K, which is not detected at room temperature due to thermal motion of the core. The spectra of 2 and 3 analyze as two quadrupole-split doublets which were assigned to the body and wing-tip pairs of metal ions. 1H NMR spectra are reported for 13 with assignment of the main resonances.