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with an S
2
magnetic ground state. Thus, this molecular material can be considered as a soft magnet
with an overall magnetic ordering below a T
C
of 4 K.
A second remarkable feature of
MOROF-1
is the reversible 'shrinking - breathing' of its solid state
structure upon solvent uptake and release. Indeed, when
MOROF-1
is removed from the mother liquor
solution in which it was crystallized and exposed to air at room temperature, the crystalline material
loses the ethanol and water guest molecules, very rapidly becoming an amorphous material with a volume
decrease of around 30 % (Figure 2.14). Even more interesting is the fact that the evacuated sample of
MOROF-1
recovers its original crystallinity and up to 90 % of its original size after exposure to liquid or
vapour ethanol solvent. The quasi-reversible process also occurs with methanol, but not with other organic
solvents, therefore showing a large selectivity for small alcohols. Thus, apparently
MOROF-1
behaves
as a sponge-like magnet material selective towards methanol and ethanol. The chemical, structural and
morphological quasi-reversibility is also accompanied by changes in the magnetic properties that are macro-
scopically detected. Magnetic properties of an evacuated amorphous sample of
MOROF-1
show similar
magnetic behavior to that shown by the as-synthesized crystals of
MOROF-1
, with the exception that its
critical temperature is one order of magnitude lower, around 0.4 K. Thus, the most striking feature exhibited
by
MOROF-1
is that the structural and chemical evolution of the material in the process of solvent inclu-
sion can be completely monitored either by the magnetic properties or its X-ray diffraction pattern. When
MOROF-1
is again re-immersed in ethanol, a fast recovery of up to 60 % of the signal can be seen during
the first minutes, whereupon the recovery of magnetic signal seems to be linear with the logarithm of time.
Two new supramolecular cobalt(II)-based coordination polymers, [Co(
13
)(4,4
-bpy)(H
2
O)
3
]
=
1
/
·
2H
2
O(
MOROF-2
)andCo
6
(
13
)
4
(py)
17
(H
2
O)
4
-(C
2
H
5
OH) (
MOROF-3
) have also been reported.
60,49
·
6C
2
H
5
OH
Crystalline
Amorphous
EtOH, H
2
O
air
EtOH, MeOH
Figure2.14
Imagesof a singlecrystalof
MOROF-1
followedwithan opticalmicroscope.The top seriesshow
the 'shrinking' process, in which a crystal of
MOROF-1
exposed to the air experiences a volume decrease of
around30%.Inthelowerseries,thesamecrystalexposedagainsttoethanolliquidbeginstoswell.Thescheme
represents the structural changes of
MOROF-1
in contact or not with ethanol or methanol solvent. (Reprinted
with permission from [56]. Copyright 2004 Royal Society of Chemistry.) A full-colour version of this figure
appearsintheColourPlatesectionof this topic.
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