Electronic localization versus delocalization: a dimetal approach
A series of dimolybdenum compounds having a Mo2
4+ core coordinated by various
ligands, including formamidinate (e.g. DAniF = N, NN-di-p-ansisylformamidinate ), acetate
and/or acetonitrile molecules, have been synthesized as building blocks for the construction
of Mo2-containing supramolecular arrays. Compound Mo2(DAniF)3(O2CCH3) was
specifically designed for the preparation of dimolybdenum pairs, whereas the others meet
the needs of Mo2
4+ units for different geometry settings.
Compounds described by a general formula [Mo2]L[Mo2], where [Mo2] =
[Mo2(DAniF)3]+, have two dimetal units electronically coupled by the central unit L , which
consequently engender significant impact on the redox property and electronic structure of
the molecule. It is found that in the weakly coupled complex system, [Mo2]M(OCH3)4[Mo2]
(M = Zn and Co), the mixed-valence complexes present asymmetric molecular structures
with two distinct [Mo2] units corresponding to be a bond order 4.0 (F2B4*2) and 3.5
(F2B4*1), respectively. EPR and magnetic susceptibility measurements for the doubly
oxidized species show that there is no significant antifferromagnetic spin coupling.
Electron delocalization occurs in the complex system where a N, N'-dimethyloxamidate binds two [Mo2] units within two fused six-membered rings. In this
case, the mixed-valence complex has a symmetric molecular structure, implying that the
odd electron is fully delocalized over two [Mo2]units. Strong metal-metal interaction is also
evidenced by intervalence charge transfer of the mixed-valence species and the diamanetism
of the doubly oxidized complex.
Remarkably, two isomers varying in linkage conformation, namely, alpha and beta, have
been isolated as diaryloxamidate ligands are used as the linker. Studies on the neutral and
the oxidized compounds of the two isomers by employing various techniques consistently
show that in the alpha form intramolecular electron transfer is blocked , while in the beta form, the electrons are delocalized over the two [Mo2] units. Thus, the mixed-valence complexes
of the two isomers are appropriately described by alpha-[Mo2]0(oxamidate)[Mo2]1+ and beta-
Advisor:Cotton, F. Albert; Fackler, John P.; Gabbai, Francois, P; Tsai, Jerry W.
School:Texas A&M University
School Location:USA - Texas
Source Type:Master's Thesis
Keywords:electron delocalization metal bond dimolybdenum mixed valence compound
Date of Publication:05/01/2003