SYNTHESIS, CHARACTERIZATION, AND CRYSTAL-STRUCTURE OF A (MU-OXO)BIS(MU-ACETATO)DIIRON(III) COMPLEX WITH A DINUCLEATING HEXAPYRIDINE LIGAND,1,2-BIS[2-(BIS(2-PYRIDYL)METHYL)-6-PYRIDYL]ETHANE - THE FIRST EXAMPLEOF A DISCRETE (MU-OXO)BIS(MU-ACETATO)DIIRON(III) COMPLEX WITH A DINUCLEATING LIGAND

A mononucleating tripyridine ligand, 2-(bis(2-pyridyl)methyl)-6-methyl pyridine (L(1)), and a dinucleating hexapyridine ligand, 1,2-bis[2-(bi s(2-pyridyl)methyl)-6-pyridyl]ethane (L(2)), have been prepared. The r eaction of a carbanion of 2,6-lutidine with 2-bromopyridine affords L( 1) which is converted to LJ quantitatively by treating with tert-butyl lithium and 1,2-dibromoethane. (mu-Oxo)bis(mu-acetato)diiron(III) comp lexes [Fe-2(O)(OAc)(2)(L(1))(2)](ClO4)(2) (1) and [Fe-2(O)(OAc)(2)L(2) ](ClO4)(2) (2) have been synthesized and characterized by means of inf rared, UV/vis, mass, and Mossbauer spectroscopies and by measuring mag netic susceptibility and cyclic voltammograms. All the spectral data a re consistent with the (mu-oxo)bis(mu-acetato)diiron(III) core structu re in both 1 and 2. A relatively strong molecular ion peak at m/z 865 corresponding to [{Fe2O(OAc)(2)L(2)}(ClO4)](+) in a FAB mass spectrum of 2 suggests the stabilization of the (mu-oxo)bis(mu-acetato)diiron(I II) core structure by L(2) in a solution state. The compound 2 . DMF . 2-PrOH . H2O, chemical formula C44Cl2Fe2H51N7O16, crystallizes in the monoclinic space group C2/c with a 22.034(6) Angstrom, b = 12.595(5) Angstrom, c = 20.651(7) Angstrom, beta 121.49(2)degrees, and Z = 4. Th e cation has 2-fold symmetry with the bridging oxygen atom on the 2-fo ld axis: Fe-(mu-O) = 1.782(5) Angstrom, Fe-O-Fe = 123.6(6)degrees, and Fe ... Fe = 3.142(3) Angstrom. The diiron(III) core structure of 2 se ems to be stabilized by encapsulation of the ligand. Compound 2 is the first example of a discrete (mu-oxo)bis(mu-acetato)diiron(III) comple x with a dinucleating ligand.