INQUIMAE   12526
INSTITUTO DE QUIMICA, FISICA DE LOS MATERIALES, MEDIOAMBIENTE Y ENERGIA
Unidad Ejecutora - UE
artículos
Título:
Ferromagnetic coupled mu-phenoxo-mu-carboxylato heterodinuclear complexes based on the Cr(salen) moiety: structural and magnetic characterization.
Autor/es:
PABLO ALBORÉS; JOHANNA SEEMAN; EVA RENTSCHLER
Revista:
JOURNAL OF THE CHEMICAL SOCIETY, DALTON TRANSACTIONS
Editorial:
Royal Society of Chemistry
Referencias:
Año: 2009 p. 7660 - 7668
ISSN:
0300-9246
Resumen:
The synthesis, crystal structure, and magneto-chemical characterization
of two new unprecedented mu-phenoxo-mu-carboxylato heterodinuclear
complexes based on the Cr(salen) moiety (salen =
N,N'-bis(salicylidene)ethylenediamine),
[M-II(O2C(CH3)(3))(OH2)(2)(mu-O2C(CH3)(3))(mu-salen)Cr-III-(O2C(CH3)(3))],
M = Ni (2), Co(3) are reported. The dinuclear complexes were obtained
starting from the mononuclear trans-[Cr(salen)(CN)(2)]PPh4 (1), whose
crystal structure is also reported. They show a trans arrangement of the
Cr(salen) unit, bridging through the phenolate O atoms to a second
metal center. An additional mu(2)-O-2-carboxylato bridge and a further
monodentating carboxylate ligand complete the roughly octahedral Cr(III)
coordination sphere. The highly distorted octahedral M(II) coordination
environment is completed by two coordinated water molecules and an
additional monodentating carboxylate. Variable-temperature solid-state
DC magnetization studies were carried out in the 2.0-300 K range.
Ferromagnetic isotropic pairwise exchange parameters were found with
values of J = 4.1 cm(-1) (2) and J = 2.1 cm(-1) (3). Additionally, for
complex 3, a ZFS parameter, D, was employed to properly fit the
experimental data. Magnetization (M) vs. field (H) and temperature (T)
data further support the presence of this anisotropic component and
confirm ground states S = 5/2 and S = 3 for 2 and 3, respectively.
Broken symmetry DFT calculations properly reproduce the experimental J
values supporting the ferromagnetic exchange interaction experimentally
observed. No out of phase susceptibility signal was observed in 0 DC
magnetic field for both complexes. However, in the case of complex 3 a
non-zero chi '' is observed when a small external field is applied below
3 K, suggesting slow relaxation of the magnetization which at 0 DC
field is suppressed, probably due to efficient tunnelling relaxation
pathways. The low symmetry of the Co(II) site in complex 3 may lead to
the presence of transversal anisotropic components which could be
responsible for the enhanced tunnelling pathway.