title: Hexanuclear iron(III) salicylaldoximato complexes presenting the [Fe6(mu3-O)2(mu2-OR)2]12+ core: syntheses, crystal structures, and spectroscopic and magnetic characterization.
abstract: The use of salicylaldehyde oxime (H2salox) in iron(III) carboxylate chemistry has yielded two new hexanuclear compounds [Fe6(mu3-O)2(O2CPh)10(salox)2(L)2].xMeCN.yH2O [L = MeCONH2, x = 6, y = 0 (1); L = H2O, x = 2, y = 3 (2)]. Compound 1 crystallizes in the triclinic space group P with (at 25 degrees C) a = 13.210(8) A, b = 13.87(1) A, c = 17.04(1) A, alpha = 105.79(2) degrees , beta = 96.72(2) degrees , gamma = 116.69(2) degrees , V = 2578.17(2) A(3), and Z = 1. Compound 2 crystallizes in the monoclinic space group C2/c with (at 25 degrees C) a = 21.81(1) A, b = 17.93(1) A, c = 27.72(1) A, beta = 111.70(2) degrees , V = 10070(10) A(3), and Z = 4. Complexes 1 and 2 contain the [Fe6(mu3-O)2(mu2-OR)2]12+ core and can be considered as two [Fe3(mu3-O)] triangular subunits linked by two mu2-oximato O atoms of the salox2- ligands, which show the less common mu3:eta1:eta2:eta1 coordination mode. The benzoato ligands are coordinated through the usual syn,syn-mu2:eta1:eta1 mode. The terminal MeCONH2 ligand in 1 is the hydrolysis product of the acetonitrile solvent in the presence of the metal ions. Mössbauer spectra from powdered samples of 2 give rise to two well-resolved doublets with an average isomer shift consistent with that of high-spin Fe(III) ions. The two doublets, at an approximate 1:2 ratio, are characterized by different quadrupole splittings and are assigned to the nonequivalent Fe(III) ions of the cluster. Magnetic measurements of 2 in the 2-300 K temperature range reveal antiferromagnetic interactions between the Fe(III) ions, stabilizing an S = 0 ground state. NMR relaxation data have been used to investigate the energy separation between the low-lying states, and the results are in agreement with the susceptibility data.
authors.affiliation: Institute of Materials Science, NCSR Demokritos, 15310 Aghia Paraskevi, Athens, Greece. craptop@ims.demokritos.gr
authors.forename: Catherine P
authors.initials: CP
authors.lastname: Raptopoulou
authors.forename: Athanassios K
authors.initials: AK
authors.lastname: Boudalis
authors.forename: Yiannis
authors.initials: Y
authors.lastname: Sanakis
authors.forename: Vassilis
authors.initials: V
authors.lastname: Psycharis
authors.forename: Juan Modesto
authors.initials: JM
authors.lastname: Clemente-Juan
authors.forename: Michael
authors.initials: M
authors.lastname: Fardis
authors.forename: George
authors.initials: G
authors.lastname: Diamantopoulos
authors.forename: George
authors.initials: G
authors.lastname: Papavassiliou
mesh_terms: D015392:Chemistry, Inorganic / Q000379:methods; D018360:Crystallography, X-Ray; D058085:Iron Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008280:Magnetics; D015394:Molecular Structure; D015204:Spectroscopy, Mossbauer
chemical_list: D058085:Iron Compounds