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results show that cage 1 has a gradual spin crossover behavior,
and its transition temperature T1/2 is around 256 K, slightly
lower than room temperature. The multiple down-up
magnetic cycles measurement confirms that the SCO is
reversible and stable. Despite many attempts, the
determination of the crystal structures with different spin
states failed due to the very rapid decay of these crystals.
Compared with 1, complex 2 is more inclined to low-spin
state (Fig. 4b). As the temperature increased from 30 to 298 K,
the MT value increased slowly from 3.47 to 5.29 cm3 mol−1 K,
indicating that 22% of the ferrous ions in 2 were in high-spin
state within the temperature range. The MT showed an
abrupt rise up to a maximum value of 17.38 cm3 K mol-1 at 400
K. This value is much lower than the theoretical value of eight
high-spin ferrous ions (MT = 24 cm3 mol−1 K, g = 2.0). The
results show that about 72% of the ferrous metals are in high-
spin state at 400 K. Therefore, 2 exhibited incomplete spin
crossover behaviour in the range of test temperature.
Compared with 1, the inclusion of I2 and TTF resulted in
stabilization of the high-spin state of iron(II) centers in the
host-guest material [I2/TTF1] (Fig. 4a). For [I2/TTF2], the
guest changed its spin-crossover behaviors slightly (Fig. 4b). 2
is less affected by the TTF/I2 mixtures due to the TTF radical
cation. The difference of the magnetic behaviour between
I2/TTF1 and I2/TTF2 was explained by the different degrees
of interaction between the guest molecules and host
assemblies. 1 adsorbed more guest molecules than 2, and
I2/TTF1 was more inclined to possess high-spin state than
I2/TTF2. This is in consistent with other reported porous SCO
compounds, in which the guest molecules caused assemblies
to move high-spin state.16
DOI: 10.1039/D0DT00353K
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of which synergistically adsorbing I2 and TTF, and showing solid
state spin-crossover behaviors. To the best of our knowledge,
these are the rare supramolecular assemblies based on cubic
SCO cages with 3D connected porous. We believe that these
results will initiate the search for other supramolecular
assemblies with polyhedral metal organic cages as building
blocks.
This work was supported by the National Natural Science
Foundation of China (21771089), the Fundamental Research
Funds for the Central Universities (JUSRP21936,
JUSRP51725B),
the project for Jiangsu scientific and technological innovation
team, and the MOE & SAFEA for the 111 Project (B13025). We
gratefully thank the members of the Central Laboratory,
School of Chemical and Material Engineering, Jiangnan
University for help with experimental methodologies.
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Conflicts of interest
There are no conflicts to declare.
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Notes and references
1
(a) H. Furukawa, K. E. Cordova, M. O'Keeffe and O. M. Yaghi,
The chemistry and applications of metal-organic frameworks,
Science, 2013, 341, 1230444; (b) Y. Bai, Y. Dou, L.-H. Xie, W.
4 | J. Name., 2012, 00, 1-3
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