Conformation and electronic configuration of complexes with multiple dimetal units
Date
2009-05-15
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Abstract
By using the building blocks Mo2(DAniF)3(O2CCH3) (DAniF = N,N'-di-panisylformamidinate)
and [Mo2(cis-DAniF)2(NCCH3)4](BF4)2, a series of complexes with
multiple dimolybdenum units, bridged by a variety of linkers and having various
oxidation states, has been synthesized and studied by various physical and chemical
methods.
The isomeric neutral diamidate-bridged molecules, α– and β–
(DAniF)3Mo2(ArN(O)CC(O)NAr)Mo2(DAniF)3 (Ar = p-anisyl), have been oxidized to
give the PF6 salts of the four cations α1+, α2+, β1+, β2+; all four structures together with
supporting evidence show that in α1+
and α2+ the unpaired electrons are localized while in
β1+ and β2+ they are delocalized in the time scale of these experiments.
It is also found that a hydroxide bridged complex having a [Mo2](µ-OH)2[Mo2]
core undergoes a oxidative deprotomation, both in solution and in crystals, to a
compound with a [Mo2](µ-O)2[Mo2] core. A probable key intermediate with one OH and
one O bridge has also been characterized.
One electron oxidation of the tetrabridged compounds [Mo2(cis-DAniF)2]2(µ-X)4,
where X is a halogen atom (Cl, Br, I), produces a decrease of about 0.24 Å in the
separation between the midpoints of the multiply bonded dimolybdenum units. DFT calculations suggest partial bond formation during the oxidation, which is consistent with
NIR, EPR and electrochemical measurements.
Additionally, a pair of isomeric cyclic triads containing three [Mo2(cis-DAniF)2]2+
units, bridged by six fluoride anions, have been synthesized and crystallographically
characterized. The symmetry of the α isomer is C2v because the three [Mo2] units are
oriented in two orthogonal directions while that of the other isomer is D3h because the
three [Mo2] units are parallel. No direct interconversion between isomers has been
detected by heating or irradiation of solutions but oxidation of the α isomer first generates
an α+ species that changes to β+.
Finally, reaction of [Mo2(cis-DAniF)2(NCCH3)4](BF4)2 and Bun
4NBH4 in ether
gives [Mo2(cis-DAniF)2]2(µ-H)4 (14), a compound whose Mo4H4 core may be described
as an elongated tetrahedron in which the four H atoms are along the four long edges and
the Mo2 units along the short edges.
Description
Keywords
conformation, electronic configuration