PROPERTIES AND REACTIVITY OF UNUSUAL DIIRON COMPLEXES OF A LINEAR TETRADENTATE LIGAND - CRYSTAL-STRUCTURES OF DIIRON-(II) AND DIIRON-(III) COMPLEXES

Dinuclear iron complexes containing the tetradentate N-4 ligand thyl-N ,N'-bis(2-pyridyl-methyl)-ethane-1,2-diamine (L) have been prepared. T he diiron(II) complex [LFe(O(2)CMe)(2)FeL]-[ClO4](2) 1 has been charac terized by X-ray crystallography: triclinic, space group P $($) over b ar$$ 1 with a = 13.756(3), b = 15.033(3), c = 13.637(3) Angstrom, alph a = 97.82(1), beta = 108.95(1), gamma = 118.07(1)degrees and Z = 2. Th e structure refined to a final R value of 0.046 for 3556 reflections. The complex contains two iron(II) ions bridged by two acetate groups, Fe...Fe 4.382(2) Angstrom. Each acetate bridges the iron atoms in an O ,O' mode using the syn lone pair of one carboxylate oxygen atom and th e,anti lone pair of the other. The ligand shows a cis-a conformation a bout the iron(II) centres. Complex 1 is readily oxidized in solution b y air and from these solutions a diiron(III) complex containing a mu-o xo-mu-acetato core, [LFeO(O(2)CMe)FeL][ClO4](3), was recovered. Anothe r diiron(III); complex, prepared in the absence of other possible brid ging groups; is formulated as [LFeO(OH)FeL][ClO4](3).2H(2)O, 2. The sp ectroscopic data for it are consistent with the unusual formulation of a doubly bridged mu-oxo-mu-hydroxo-diiron(III) core, only the second reported example of a small molecule with this core structure. In solu tion, 2 is sensitive towards carbon dioxide, reacting to give [LFeO(CO 3)FeL][ClO4](2).2H(2)O, 3. The structure of 3 has been solved by X-ray crystallography and shows a dibridged mu-oxo-mu-carbonato-O,O' core: monoclinic, space group C2/c, a = 19.565(8), b = 13.427(2), c = 13.722 (9) Angstrom, beta = 94.31(3)degrees and Z=8. The structure refined to a final R value of 0.066 for 4575 reflections. The average Fe-(mu-O) is 1.804(5) Angstrom, Fe-O-Fe is 126.1(3)degrees and Fe...Fe 3.216(1) Angstrom. Again L shows a cis-alpha conformation. Complex 2 was used t o prepare other complexes containing the [LFeOFel](4+) core: [LFeO(O(2 )CMe)FeL][ClO4](3), [LFeO(O2CH)- FeL][ClO4](3) and [LFeO(SO4)FeL][ClO4 ](2), by addition of acetic acid, formic acid and sodium hydrogensulfa te respectively; and [L(Cl)FeOFe(Cl)L][ClO4](2) by addition of chlorid e ions.