Synthesis, Characterization, and Crystal Structure of a (μ-Oxo)bis(μ-acetato)diiron(III) Complex with a Dinucleating Hexapyridine Ligand, 1,2-Bis[2-(bis(2-pyridyl)methyl)-6-pyridyl]ethane. The First Example of a Discrete (μ-Oxo)bis(μ-acetato)diiron(III) Complex with a Dinucleating Ligand

A mononucleating tripyridine ligand,
2-(bis(2-pyridyl)methyl)-6-methylpyridine (L1),
and a dinucleating
hexapyridine ligand,
1,2-bis[2-(bis(2-pyridyl)methyl)-6-pyridyl]ethane
(L2), have been prepared. The reaction of
a carbanion of 2,6-lutidine with 2-bromopyridine affords L1
which is converted to L2 quantitatively by
treating
with tert-butyllithium and 1,2-dibromoethane.
(μ-Oxo)bis(μ-acetato)diiron(III) complexes
[Fe2(O)(OAc)2(L1)2](ClO4)2 (1) and
[Fe2(O)(OAc)2L2](ClO4)2
(2) have been synthesized and characterized by means of
infrared,
UV/vis, mass, and Mössbauer spectroscopies and by measuring
magnetic susceptibility and cyclic voltammograms.
All the spectral data are consistent with the
(μ-oxo)bis(μ-acetato)diiron(III) core structure
in both 1 and 2. A
relatively strong molecular ion peak at m/z 865
corresponding to
[{Fe2O(OAc)2L2}(ClO4)]+
in a FAB mass spectrum
of 2 suggests the stabilization of the
(μ-oxo)bis(μ-acetato)diiron(III) core structure
by L2 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) Å,
b = 12.595(5) Å, c = 20.651(7) Å,
β = 121.49(2)°, and Z = 4. The cation
has
2-fold symmetry with the bridging oxygen atom on the 2-fold axis: 
Fe−(μ-O) = 1.782(5) Å, Fe−O−Fe =
123.6(6)°, and Fe···Fe = 3.142(3) Å. The
diiron(III) core structure of 2 seems to be stabilized
by encapsulation
of the ligand. Compound 2 is the first example of a
discrete (μ-oxo)bis(μ-acetato)diiron(III)
complex with a
dinucleating ligand.