TRANSITION-METAL COMPLEXES WITH THIOSEMICARBAZIDE-BASED LIGANDS .13. SYNTHESIS AND STRUCTURE OF MU-OXO-BIS-((PENTANE-2,4-DIONE BIS(S-METHYLISOTHIOSEMICARBAZONATO-KAPPA-2N,N'')(3-))IRON(IV))

Reaction of S-methylisothiosemicarbazide hydroiodide, pentane-2,4-dione and sodium carbonate with iron(III) nitrate in ethanol yielded paramagnetic (mu-eff = 3.00) [FeL(I)] [L = pentane-2,4-dione bis(S-methylisothiosemicarbazonato)(3-)]. When treated with ammonia a methanolic solution of [FeL(1)] yielded the diamagnetic complex [(FeL)2O]. Its structure has been determined by X-ray crystallography, and characterized by spectroscopic measurements. The complex crystallizes in the monoclinic space group P2(1)/c with a = 11.542(1), b = 20.710(4), c = 13.232(2) angstrom, beta = 113.12(1)-degrees and Z = 4. The structure was solved by application of the heavy-atom method on the basis of 3362 reflections [l > 3-sigma(l)] and refined by full-matrix least squares to R 0.025. It consists of a binuclear complex molecule in which two iron atoms are bridged by oxygen. Both Fe atoms have approximate square-pyramidal co-ordination with the quadridentate ligand lying in the basal plane and the bridging oxygen occupying the apical position. The ligands in both halves of the molecule are saddle shaped, bent away from the apical oxygen atom and twisted around the Fe-O-Fe bridge. The Fe-O distances are 1.736(2) and 1.745(2) angstrom, Fe-N in the range 1.893(3)-1.917(2) angstrom. On the basis of the stoichiometry, crystal structure, electronic and NMR spectra, and magnetic measurements the formal oxidation state of +4 was assigned to iron in [(FeL)2O].