Novel Rectangular [Fe4(μ4-OHO)(μ-OH)2]7+ versus "Butterfly" [Fe4(μ3-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]

The preparations, X-ray structures, and detailed physical characterizations are presented for three new tetranuclear Fe-\\\/RCO2-/phen complexes, where phen = 1,10-phenanthroline: [Fe-4(OHO)(OH)(2)(O2CMe)(4)(phen)(4)](CIO4)(3).4.4MeCN.H2O (1.4.4MeCN.H2O); [Fe4O2(O2CPh)(7)(phen)(2)](CIO4).2MeCN (2.2MeCN); [Fe4O2(O2CPh)(8)(phen)(2)]-2H(2)O (3.2H(2)O). Complex 1.4.4MeCN.H2O crystallizes in space group P2(1)/n, with a = 18,162(9) Angstrom, b = 39.016(19) Angstrom, c = 13.054(7) Angstrom, beta = 104.29(2)degrees, Z = 4, and V = 8963.7 Angstrom(3). Complex 2.2MeCN crystallizes in space group P2(1)/n, with a = 18.532(2) Angstrom, b = 35.908(3) Angstrom, c = 11.591 (1) Angstrom, beta = 96.42(l)degrees, Z = 4, and V = 7665(l) Angstrom(3). Complex 3.2H(2)O crystallizes in space group /2/a, with a = 18.79(1) Angstrom, b = 22.80(1) Angstrom, c = 20.74(1) Angstrom, beta = 113.21(2)degrees, Z = 4, and V = 8166(1) Angstrom(3). The cation of 1 contains the novel [Fe-4(mu(4)-OHO)(mu-OH)(2)](7+) core. The core structure of 2 and 3 consists of a tetranuclear bis(mu(3)-O) cluster disposed in a "butterfly" arrangement. Magnetic susceptibility data were collected on 1-3 in the 2-300 K range. For the rectangular complex 1, fitting the data to the appropriate theoretical chi(M) vs T expression gave J(1) = -75.4 cm(-1), J(2) = -21.4 cm(-1), and g = 2.0(1), where J(1) and J(2) refer to the (FeO)-O-\\\(O2CMe)(2)Fe-\\\ and Fe-\\\(OH)Fe-\\\ 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 Fe-\\\ ions. The exchange coupling constant J(bb) ("body-body" interaction) is indeterminate due to prevailing spin frustration, but the "wing-body" antiferromagnetic interaction (J(wb)) was evaluated to be -77.6 and -65.7 cm(-1) for 2 and 3, respectively, using the appropriate spin Hamiltonian approach. Mossbauer spectra of 1-3 are consistent with high-spin Fe-\\\ 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. H-1 NMR spectra are reported for 1-3 with assignment of the main resonances.