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A Highly Porous Metal–Organic Framework
FULL PAPER
Table 1. Crystallographic data for SNU-77, SNU-77’, SNU-77R, SNU-77S, and SNU-77H.
activated by treatment with su-
percritical CO2 (see the Experi-
mental Section), a single crystal
SNU-77[a]
SNU-77’[a]
SNU-77R
SNU-77S
SNU-77H[a]
formula
crystal system
space group
Mr
Zn4C78H48N2O13 Zn4C78H48N2O13 Zn4C78H48N2O13 Zn4C78H48N2O13 Zn4C78H48N2O13
cubic
cubic
cubic
cubic
cubic
Ia-3
1482.76
32.2713(18)
33609(3)
8
0.586
293
0.71073
0.591
0.868
of [Zn4OACTHUNGTERNNU(G TCBPA)2] (SNU-77S)
Pa-3
Pa-3
Pa-3
Pa-3
resulted. The X-ray crystal
structure of SNU-77S is similar
to that of SNU-77R, as shown
in Figure 1, which indicates that
treatment with supercritical
CO2 is as mild as room-temper-
ature evacuation and induces
rather small structural rear-
rangements.
1482.76
32.6570(9)
34828.0(17)
8
1482.76
32.5926(6)
34622.4(11)
8
1482.76
32.407(5)
34034(9)
8
1482.76
32.4053(7)
34028.9(13)
8
a [ꢀ]
V [ꢁ3]
Z
1calcd [gcmꢀ3
T [K]
]
0.566
0.569
0.579
0.579
293
293
293
293
l [ꢁ]
0.71073
0.570
0.703
0.71073
0.574
0.796
0.0522, 0.1337
0.1222, 0.1465
0.71073
0.584
1.072
0.0925, 0.2503
0.2025, 0.3318
0.71073
0.584
1.053
0.0883, 0.2459
0.2219, 0.3348
m [mmꢀ1
]
GOF (F2)
[c]
R1,[b] wR2 [I>2s(I)] 0.0890, 0.2052
0.0957, 0.2470
0.2028, 0.2852
[c]
R1,[b] wR2 (all data) 0.2182, 0.2327
Interestingly,
however,
[a] The residual electron densities were flattened by using the SQUEEZE option of PLATON. [b] R=SjjFo j
[Zn4O(TCBPA)2] (SNU-77H),
AHCTUNGTRENNUNG
1
2
2
2
2
ꢀjFcjj/SjFo j. [c] wR(F2)=[Sw
N
E
G
+
2
which was obtained by heating
SNU-77’ at 1108C under a pres-
2
2
2Fc2)/3 for SNU-77, w=1/[s
G
N
(0.1696P)2 +(26.59)P], P=(Fo2 +2Fc2)/3 for SNU-77R, w=1/[s
2(Fo )+(0.1776P)2 +(4.96)P], P=(Fo2 +2Fc2)/3
2
sure of 10ꢀ5 torr for 2 h, exhibits
2
for SNU-77S, and w=1/[s
2(Fo )+(0.1569P)2 +(0.000)P], P=(Fo2 +2Fc2)/3 for SNU-77H.
a significantly different struc-
ture to those of SNU-77, SNU-
77’, SNU-77R, and SNU-77S.
When crystals of SNU-77 were immersed in toluene for
24 h, the DMA guest molecules were exchanged with tolu-
ene to yield [Zn4OACHTUNGTRENNUNG(TCBPA)2]·14PhCH3·3H2O (SNU-77’), as
characterized by IR spectroscopy, elemental analysis, and
TGA. The X-ray crystal structure of SNU-77’ is very similar
to that of SNU-77 (Figure 1).
The crystal space group is Ia-3, compared with Pa-3 for the
others, and only one kind of TCBPA3ꢀ unit exists. Most im-
portantly, the TCBPA3ꢀ unit within the structure exhibits
large rotational rearrangements: The dihedral angle be-
tween the outer phenyl rings of the biphenyl groups located
in the trans positions around the Zn4O cluster is 0.08, com-
pared with 79.1(1)8 in SNU-77’ and 68.6(3)8 in SNU-77R,
and the dihedral angles between the two phenyl rings of the
biphenyl groups in TCBPA3ꢀ are 8.7(3)8, compared with an
average of 30.5(1)8 in SNU-77’ and an average of 30.3(3)8 in
SNU-77R (Figure 1). Face-to-face p–p interactions exist be-
tween two interpenetrating nets in SNU-77H [the shortest
C–C distance, 3.693(2) ꢁ; dihedral angle, 8.8(4)8], in con-
trast to edge-to-face p–p interactions in the others (Fig-
ure S2). The effective window size (8.1ꢂ4.1 ꢁ) is larger than
those of SNU-77’, SNU-77R, and SNU-77S. The void
volume of SNU-77H estimated by PLATON[29] is 69.1%
(1.18 cm3 gꢀ1).
When SNU-77’ was activated at room temperature under
a pressure of 10ꢀ5 torr for 24 h, [Zn4O
ACTHNUGTRNE(NUG TCBPA)2] (SNU-
77R) resulted. The X-ray diffraction data of SNU-77R col-
lected at room temperature indicates that many of its key
dihedral angles are different to those of SNU-77 and SNU-
77’. In particular, the dihedral angle between the two outer
phenyl rings of the ligands located in the trans positions
around the Zn4O cluster is 68.6(3)8 compared with 79.1(1)8
in SNU-77’, and the dihedral angles between the inner
phenyl rings of TCBPA1 and TCBPA2 are 76.9(3) and
59.7(8)8, respectively, compared with 74.5(1) and 72.0(1)8 in
SNU-77’ (Figure 1). These angles indicate that the phenyl
rings in TCBPA3ꢀ in the framework rotate upon removal of
the guests even at room temperature. SNU-77R exhibits
edge-to-face p–p interactions between two interpenetrating
nets [the shortest C–C distance, 3.806(30) ꢁ], but the dihe-
dral angle [24.6(7)8] is remarkably different to that in SNU-
77’ [48.3(1)8; Figure S2]. Due to these rotational rearrange-
ments, the shape of the channel is different to that of SNU-
77’ and the effective window size is enlarged to 7.7ꢂ4.4 ꢁ
compared with 4.1ꢂ4.9 ꢁ for SNU-77’. A few examples of
enlarged pore windows on desolvation have been reported
in the literature.[27,28] The void volume of SNU-77R estimat-
ed by PLATON[29] is 69.9% (1.21 cm3 gꢀ1), similar to the
value of 70.3% (1.24 cm3 gꢀ1) for SNU-77.
The major structural differences between SNU-77’
AHCTUNGTREG(NNUN =SNU-77), SNU-77R (=SNU-77S), and SNU-77H are the
effective window sizes and shapes, which are determined by
the dihedral angles between the phenyl rings around a Zn4O
cluster (Table 2), although they have similar cell parameters
and only 2.3–3.0% differences in cell volumes. SNU-77R
and SNU-77S have intermediate structures between SNU-
77’ and SNU-77H. Despite the different fine structures re-
vealed by the single-crystal X-ray data, the simulated
powder X-ray diffraction (PXRD) patterns of SNU-77R,
SNU-77S, and SNU-77H are very similar: Only the small
peaks at 2q=9.4, 10.1, and 11.28 for SNU-77 and SNU-77’
are significantly weaker in the patterns of SNU-77R and
SNU-77S, and they disappear in SNU-77H (Figure S3). This
indicates that the rearrangements of the molecular compo-
nents can barely be recognized by the PXRD patterns
unless extremely careful attention is paid to the very small
peaks.
Supercritical drying is a common washing method in poly-
mer synthesis and aerogel production. Recently, supercriti-
cal CO2 drying has been applied to MOFs as an efficient ac-
tivation method that leads to increased surface areas of the
MOFs.[14] In this study, when single crystals of SNU-77 were
Chem. Eur. J. 2011, 17, 7251 – 7260
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
7253