Polymorphic Coordination Networks Responsive to CO2, Moisture and Thermal Stimuli : Porous Cobalt(II) and Zinc(II) Fluoropyrimidinolates
Articolo
Data di Pubblicazione:
2008
Citazione:
Polymorphic Coordination Networks Responsive to CO2, Moisture and Thermal Stimuli : Porous Cobalt(II) and Zinc(II) Fluoropyrimidinolates / S. Galli, N. Masciocchi, G. Tagliabue, A. Sironi, E. Barea, J. M. Salas, L. Mendez, M. Domingo, M. Perez-Mendoza and J. A. R. Navarro. - In: CHEMISTRY-A EUROPEAN JOURNAL. - ISSN 0947-6539. - 14:32(2008), pp. 9890-9901.
Abstract:
The novel porous [{MACHTUNGTRENUNG(F-pymo)
2}n]·2.5nH2O coordination networks
(M=Co, Zn; F-pymo=5-fluoropyrimidin-
2-olate), possessing sodalitic topology,
have been synthesised and structurally
characterised by means of
powder diffraction methods. Thermodiffractometry
demonstrated their plasticity:
when heated up to 363 K, they
reversibly transform into three-dimensional
dehydrated [{MACHTUNGTRENUNG(F-pymo)2}n] species,
with significantly different lattice
parameters. Further heating induces irreversible
polymorphic transformations
into layered phases, in which the original
MN4 coordination sphere changes
into an MN3O one. A mixed-metal
phase, [{CoxZn1 xACHTUNGTRENUNG(F-pymo)2}n]·2.5nH2O,
was also prepared, showing that zinc is preferentially inserted, when starting
from a Co/Zn reagent ratio of 1:1. The
solid–gas adsorption properties of the
anhydrous 3D frameworks have been
explored towards N2, H2 (77 K) and
CH4, CO2 (273 K). These results show
that these materials permit the diffusion
of CO2 molecules only. Remarkably,
the CO2 adsorption process for the
[{CoACHTUNGTRENUNG(F-pymo)2}n] network proceeds in
two steps: the first step takes place at
low pressures (<600 kPa) and the
second one above a threshold pressure
of 600 kPa. By contrast, the [{ZnACHTUNGTRENUNG(Fpymo)
2}n] network only permits CO2
diffusion by applying pressures above
900 kPa. This type of behaviour is typical
of porous networks with gated
channels. The high CO2 selectivity of
these systems over the rest of the essayed
probe gases is explained in terms
of flexibility and polarity of the porous
network. Finally, the magnetic studies
on the CoII systems reveal that the as
synthesised [{CoACHTUNGTRENUNG(F-pymo)2}n]·2.5nH2O
material behaves as an antiferromagnet
with a TN of about 29 K. At variance,
the [{CoACHTUNGTRENUNG(F-pymo)2}n] layered phase
shows an unusually weak ferromagnetic
ordering below 17 K, arising from a
spin-canting phenomenon.
Tipologia IRIS:
01 - Articolo su periodico
Keywords:
Adsorption; Cobalt; Metal-organic frameworks; X-ray diffraction; Zinc
Elenco autori:
S. Galli, N. Masciocchi, G. Tagliabue, A. Sironi, E. Barea, J. M. Salas, L. Mendez, M. Domingo, M. Perez-Mendoza and J. A. R. Navarro
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