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The magnetic properties of j[(tacn)6Fe8(M3-0)2(M2-0H)12]Br7(H20)}Br'H20, Fe8, tacn = 1,4,7-triazacyclononane, a molecule comprising eight iron(III) ions bridged by oxo and hydroxo groups, are reported. The magnetic susceptibility, both dc and ac, and the magnetization indicate that at low-temperature spin levels with 8 < S < 10 are populated. EPR confirms that levels of high spin multiplicity are populated at 4.2 K. For the first time an attempt is made to calculate the energy of the spin levels of such a large cluster within a spin Hamiltonian formalism. The 1 679 616 states originating from the coupling of eight S = s/2 spins are classified by using total spin and point group symmetry, and the Hamiltonian matrix is calculated using an irreducible tensor operator approach. In this way the susceptibility can be calculated, and satisfactory fits of the experimental magnetic susceptibility are achieved. The values of the required parameters compare well with those previously reported in analogous iron complexes.

Veterinary anti-inflammatory Cu(II) complexes of indomethacin (1-(4-chlorobenzoyl)-5-methoxy-2-methyl-1H-indole-3-acetic acid = IndoH), of the general formula [Cu(2)(Indo)(4)L(2)] (L = N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methylpyrrolidone (NMP), and water), were studied by zero-field and X-band EPR spectroscopies, electronic spectroscopy, magnetic measurements, and X-ray powder diffraction. The complexes are similar to Cu(II) acetate monohydrate, with a strong antiferromagnetic exchange interaction, J, ranging from -141 to -152 cm(-)(1). Variable temperature magnetic susceptibility data for all of the complexes are similar, with the exception of a [Cu(2)(Indo)(4)(H(2)O)(2)] complex, which displays an unusual increase in magnetic moment with decreasing temperature from 50 to 10 K. The X-ray powder diffraction patterns of the DMF and DMA dimers show that they are isostructural. Two isostructural H(2)O complexes were synthesized from different methods yet displayed different variable temperature magnetic susceptibity data. All of the [Cu(2)(Indo)(4)L(2)] complexes crystallize in the triclinic space group P&onemacr;. Single-crystal X-ray diffraction analysis of the DMF complex, [Cu(2)(Indo)(4)(DMF)(2)].1.6(DMF), shows that it is similar to the previously reported [Cu(2)(Indo)(4)(DMSO)(2)] with a Cu-Cu bond length of 2.630(1) Å, Cu-O(RCOO) of 1.960(4)-1.967(4) Å, and Cu-O(DMF) of 2.143(5) Å and crystal parameters a = 10.848(3) Å, b = 13.336(6) Å, c = 16.457(4) Å, alpha = 104.67(3) degrees, beta = 100.94(2) degrees, and gamma = 107.16(3) degrees. The X-ray structure of the DMF dimer does not exhibit strong intermolecular interactions due to the hydrophobic nature of the exterior. This may be important in facilitating its dissolution in micelles and transport through membranes.