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Description:
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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 -
[Mo2]0 .5+ (oxamidate )[Mo2]0 .5+ respectively . |