This work focuses the syntheses and magnetic

This work focuses the syntheses and magnetic studies
of new molecular manganese-oxo clusters using oxime-based ligands and
covalently bonded supramolecular aggregates of single-molecule magnets (SMMs).
Employing 1,3-phenylenebis(pyridin-2-ylmethanone)
dioxime (1,3-ppmdH2), 1,4-phenylenebis(pyridin-2-ylmethanone)
dioxime (1,4-ppmdH2) and 1,4-naphthalenebis(pyridine-2-ylmethanone)
dioxime (1,4-npmdH2) in the reaction with non-SMM MnIII3O(O2CR)6(py)3(ClO4)
(R = Me, Ph) complex yielded one dimeric Mn32 and two
octameric Mn38 supramolecules. The dimer consists of
two MnIII3+7 triangular units linked by
three 1,3-ppmd2- groups while octameric complexes have symmetric
cubic shapes and each consists of eight MnIII3+7
units linked covalently either by the 1,4-ppmd2- or by the 1,4-npmd2-
groups through the edges of the cubes. Solid state dc and ac magnetic
susceptibility studies revealed that each Mn3 unit is still an SMM
with ground-state spin of S = 6.
Magnetization vs. dc-field sweeps on a single crystal of Mn32
below 1.3 K exhibited hysteresis loops that showed ferromagnetically coupled
exchange-biased quantum tunneling of magnetization (QTM) steps whereas that of
Mn38 complex (using 1,4-ppmd2-) displayed
hysteresis loop below 1.2 K with antiferromagnetically coupled exchange-biased
QTM steps, confirming Mn32 and Mn38
to be supramolecular aggregates of two and eight weakly exchange-coupled SMM
units, respectively. Supramolecular octamer, Mn38, is
the highest nuclearity member of supramolecular aggregates of Mn3
SMMs whereas supramolecular dimer, Mn32, is a rare
molecular magnet to exhibit ferromagnetically coupled exchange-bias in QTM
steps and the inter-SMM coupling through 1,3-ppmd2- groups was found
to be very weak, J ~ +0.0065 K.

           Two salicyloxime derivatives, 2,2′-dihydroxy benzophenone oxime
(dboH3) and 3-methoxy-2-hydroxybenzaldoxime or
vanillin oxime (vanoxH2), have been introduced
for the first time in manganese cluster chemistry. Four new clusters including
Mn7, Mn3 and two Mn6 were synthesized. Solid
state dc and ac magnetic susceptibility measurements revealed that Mn7,
Mn3 and two Mn6 complexes have ground-state spin of 11/2,
3 and 4, respectively.  Mn7
and Mn6 clusters appear to be good single-molecule magnets while Mn3
is a scalene triangle with unprecedented ground-state spin, S = 3.

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          The syntheses, crystal structures and magnetic properties were
reported for two new
mixed-valence Mn clusters,

 (Mn9) and

 (Mn14). They were obtained from the
respective reactions of Mn12O12(O2CR)16(H2O)4
(R = Me, Ph) with eight equivalents of mpkoH in acetonitrile. Where mpkoH is
methyl(pyridine-2-yl)ketone oxime. Variable-temperature, solid-state dc and ac magnetic
susceptibility measurements established that Mn9 and Mn14
possess ground state spins of S = 3/2
and S = 1, respectively, which was
confirmed by ac in-phase susceptibility data.

          An alternate and direct synthetic
approach have been employed to synthesize rectangular Mn34pdpd
tetramer by using one-pot reaction of MnII salt and pdpdH2.
This complex was previously reported and synthesized by using preformed non-SMM
Mn3 cluster and pdpdH2. Solid state dc and ac magnetic
susceptibility measurements suggested that Mn3 units have S = 6 ground-state. The
syntheses and characterizations of a dioxime linker (dpdH2), which
was used to synthesize Mn32dpd dimer (previously
reported); a tetraoxime (ppdtH4) and a triacid (ttbaH3)
linkers, which can potentially be used for the construction of supramolecular
aggregates of Mn3 SMMs, will also be described. 

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