Structure and charge control in metal-organic frameworks based on the tetrahedral ligand tetrakis(4-tetrazolylphenyl)methane

Article abstract of DOI:10.1002/chem.200801336

Use of the tetrahedral ligand tetrakis(4-tetrazolylphenyl)methane enabled isolation of two three-dimensional metal-organic frameworks featuring 4,6- and 4,8-connected nets related to the structures of garnet and fluorite with the formulae Mn₆(ttpm)₃·5DMF·3H₂0 (1) and Cu[(Cu₄Cl)(ttpm)₂]₂·CuCl ₂·5 DMF·11H₂O (2) (H₄ttpm = tetrakis(4-tetrazolylphenyl)methane). The fluorite-type solid 2 displays an unprecedented post-synthetic transformation in which the negative charge of the framework is reduced by extraction of copper(II) chloride. Desolvation of this compound generates Cu₄(ttpm)₂·0.7 CuCl₂ (2d), a microporous material exhibiting a high surface area and significant hydrogen uptake.

Full text of DOI:10.1002/chem.200801336

DOI: 10.1002/chem.200801336
Structure and Charge Control in Metal–Organic Frameworks Based on the
Tetrahedral Ligand Tetrakis(4-tetrazolylphenyl)methane
Mircea Dincaˇ,[a] Anne Dailly,[b] and Jeffrey R. Long*[a]
Abstract: Use of the tetrahedral ligand
tetrakis(4-tetrazolylphenyl)methane
enabled isolation of two three-dimen-
sional metal–organic frameworks fea-
turing 4,6- and 4,8-connected nets re-
lated to the structures of garnet and
fluorite with the formulae Mn6-
(2) (H4ttpm=tetrakis(4-tetrazolylphe-
nyl)methane). The fluorite-type solid 2
displays an unprecedented post-syn-
thetic transformation in which the neg-
ative charge of the framework is re-
duced by extraction of copper(II) chlo-
ride. Desolvation of this compound
generates Cu4ACHTNUTRGNE(NUG ttpm)2·0.7CuCl2 (2d), a
microporous material exhibiting a high
surface area and significant hydrogen
uptake.
Keywords: copper · manganese ·
metal–organic
frameworks
·
ACHTUNGTRENNUNG
microporous materials · tetrazoles
A
ACHTUNGTRENNUNG
Introduction
mensional frameworks are based on planar, aromatic bridg-
ing ligands that need not assemble into three-dimensional
structures. Instead, three-dimensionality in these frame-
works is enforced by the metal building units, which usually
consist of multinuclear clusters synthesized in situ from
single metal-ion precursors.[5] Although mathematical and
computational principles have been laid out to understand
and sometimes predict the topology of frameworks based on
certain cluster building units,[6] the synthetic conditions re-
quired to target a given cluster are still poorly understood.
As such, the synthesis of three-dimensional frameworks
starting from simple, two-dimensional ligands remains large-
ly a matter of trial and error.
A potentially more efficient way to synthesize three-di-
mensional metal–organic frameworks is to focus on the or-
ganic ligands rather than the metal building unit, and to uti-
lize one of the many readily available three-dimensional or-
ganic scaffolds, such as tetraphenylmethane, adamantane, or
spirane. Indeed, employing a three-dimensional bridging
Owing to their porosity and potential utility in a wide varie-
ty of applications, especially in gas storage, separations, and
catalysis, metal–organic frameworks have attracted consider-
able recent attention. In particular, reports of frameworks
with surface areas well above those of any zeolites,[1] with
high hydrogen-storage capacities,[2] or displaying unprece-
dented gas separation or catalytic properties[3] have
strengthened the wide-spread interest in the field. To con-
struct materials with such remarkable properties, researchers
must rely on somewhat serendipitous synthetic methods,
which more often than not produce materials with no per-
manent porosity. Although it is not generally possible to
predict the stability of a given framework upon guest evacu-
ation, empirical observations show that the vast majority of
permanently porous frameworks covalently extend in three
dimensions.[4] Surprisingly, however, most known three-di-
ligand promotes the formation of
a three-dimensional
ˇ
[a] M. Dinca, Prof. J. R. Long
framework, regardless of the geometry around the metal
building unit. Herein, we show that use of the tetrahedral
molecule tetrakis(4-tetrazolylphenyl)methane (H4ttpm)
leads to the formation of two new three-dimensional frame-
works with rare 4,6- and 4,8-connected topologies identical
to those of garnet (gar) and fluorite (flu).[6d] We further
show that solvent exchange in the flu-type framework coin-
cides with an anionic-to-neutral post-synthetic transforma-
tion that has not been observed in metal–organic frame-
works thus far, and that evacuation of this framework pro-
Department of Chemistry
University of California at Berkeley
Berkeley CA, 94720-1460 (USA)
Fax : (+1)510-643-3546
E-mail: jrlong@berkeley.edu
[b] Dr. A. Dailly
Chemical and Environmental Sciences Laboratory
General Motors Corporation
Warren MI, 48090 (USA)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200801336.
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FULL PAPER
duces a material with permanent porosity and high surface
area.
square-planar {Cu4Cl}7+ units are bridged by eight distinct
ttpm4ꢀ ligands to form
a three-dimensional structure
(Figure 2). Within a given {Cu4Cl}7+ unit, each Cu2+ ion is
coordinated by four nitrogen atoms and one chloride anion,
whereas pairs of neighboring Cu2+ ions are bridged by two
tetrazolate rings, such that overall, the cluster can be de-
scribed as an eight-connected node. The resulting net anion-
ic charge of the framework in 2 is balanced by extraframe-
work Cu2+ ions, which are chelated by two nitrogen atoms
on adjacent tetrazolate rings. Notably, X-ray analysis also re-
vealed that the structure of 2 includes one full equivalent of
CuCl2, such that the sixth coordination site on the intrafra-
mework Cu2+ cations is occupied by a solvent molecule
75% of the time and by a chloride anion 25% of the time.
Although square-planar clusters surrounded by eight
bridging ligands have been observed previously in the struc-
tures of Mn- and Cu-tetrazolate frameworks,[2d,11] and in Fe-,
Co-, and Cd-based carboxylate frameworks,[12] their combi-
nation here with the tetrahedral four-connected nodes corre-
Results and Discussion
The tetrahedral ligand H4ttpm was synthesized by a dipolar
[2+3] cycloaddition between NaN3 and tetra(p-cyanophe-
nyl)methane, which in turn was obtained from tetraphenyl-
methane via tetra(p-bromophenyl)methane.[7] To explore
the ability of H4ttpm to promote the formation of porous
three-dimensional metal–organic frameworks, we screened
synthetic conditions that had previously been effective in
the formation of transition-metal–tetrazolate frameworks.
Thus, solventothermal reactions between H4ttpm and Mn-
ACHTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
a
crystal of 1 revealed a structure
in which linear Mn3 clusters are
connected to six distinct ttpm4ꢀ
ligands to form a neutral three-
dimensional
framework
(Figure 1). Here, each trimetal-
lic unit consists of a central
Mn2+ ion octahedrally coordi-
nated by nitrogen atoms from
six tetrazolate rings, and two
outer Mn2+ ions, each bridged
to the central Mn2+ ion by
three tetrazolate rings and fa-
cially coordinated by three sol-
vent molecules.[8] Overall, each
trinuclear unit is surrounded by
six tetrazolate rings and can
thus be described as a six-con-
nected node. Although such
linear trimetallic units are
common in both tetrazolate-
and carboxylate-based frame-
works,[9] their unique combina-
tion here with the four-connect-
ed nodes corresponding to the
ttpm4ꢀ ligands gives rise to a
rare 4,6-connected framework
with the garnet topology (gar).
Notably, this highly-connected
topology has, to our knowledge,
only been observed once before
in a metal–organic framework:
in the structure of In3Zn2(im)12
(imꢀ =imidazolate).[10]
Figure 1. Portions of the crystal structure of 1: the four- and six-connected nodes, depicted in grey and orange
and representing ttpm4ꢀ and {Mn3(tetrazolate)6} units, respectively, combine to form a three-dimensional struc-
ture with the garnet topology. Orange, grey, and blue spheres represent Mn, C, and N atoms, respectively; sol-
vent molecules and hydrogen atoms are omitted for clarity. Selected interatomic distances [ꢁ] and angles [8]:
X-ray analysis of
a single
crystal of 2 revealed a structure
ꢀ
ꢀ
ꢀ
in which chloride-centered, Mncentral N 2.32(2), Mnexterior N 2.25(2), Mnexterior O 2.16(1), Mn···Mn 4.05(3); N-Mn-N 87(1), Mn-N-N 127(1).
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J. R. Long et al.
units showed comparatively
higher porosity, samples of
Mn
(bdt)3
and
Zn3ACHTUNGTRENNUNG(bdt)3
Unlike 1, crystals of as-syn-
thesized 2 remained intact both
during methanol exchange and,
more importantly, upon evacua-
tion at 658C under reduced
pressure. The behavior of 2 to-
wards solvent exchange and
guest evacuation is similar to
that observed previously for
Mn
G
N
8ACHTGNUTERN(NUNG CH3OH)10]2
and HCu
G
(btt3ꢀ =1,3,5-benzenetristetra-
zolate),[2d,11a] two related frame-
works containing analogous
square-planar {M4Cl}7+ building
units. In stark contrast to the
btt3ꢀ-based structures, however,
initial X-ray analysis of an
evacuated crystal of 2 revealed
a surprisingly low occupancy of
the central Clꢀ anion. This sug-
gests that methanol exchange
Figure 2. Portions of the crystal structure of 2: the four- and eight-connected nodes, depicted in grey and could in principle extract CuCl2
purple and represented by ttpm4ꢀ and {Cu4Cl(tetrazolate)8} units, respectively, combine to form a three-dimen-
sional structure with the fluorite topology. Purple, green, blue, and grey spheres represent Cu, Cl, N, and C
atoms, respectively. Solvent molecules and hydrogen atoms were omitted for clarity. Selected interatomic dis-
equivalents from 2 to provide a
neutral framework with the for-
mula Cu4ACHTUNTRGNEUNG(ttpm)2, which would
be composed entirely of chlo-
ride-voided Cu4 squares, as de-
scribed by Equation (1):
ꢀ
ꢀ
tances [ꢁ] and angles [8]: Cu Cl 2.539(1), Cu N 2.036(3), Cu···Cu 3.590(1); Cu-Cl-Cu 90, N-Cu-N 87.25(1),
92.23(1), Cu-N-N 123.88(1).
sponding to the ttpm4ꢀ ligands gives rise to another rare
Cu½ðCu4ClÞðttpmÞ2ꢁ2 ꢂ CuCl2 ! 2 Cu4ðttpmÞ2 þ 2 CuCl2
ð1Þ
net—a 4,8-connected net with the fluorite topology (flu).
Notably, the structure of 2 is isotypic with that of Cd2-
A
(tcpm)[12a] (H4tcpm=tetra(p-carboxyphenyl)methane), one
The prospect of effecting an anionic-to-neutral transfor-
mation is particularly attractive in 2 because the chloride-
defficient Cu4 squares that would be formed upon extraction
of CuCl2 could potentially serve as strong binding pockets
for small molecules, such as O2, N2, or H2. In an effort to
probe the possibility of such a transformation, we employed
a strategy involving a Soxhlet extraction of CuCl2 from a
fresh sample of 2 with hot methanol. The initially colorless
solvent gradually turned green, confirming the extraction of
CuCl2 from the crystals of 2. After five days, methanol-
washed single crystals of 2 were collected by filtration and
evacuated at 658C under reduced pressure to produce Cu4-
of only two other examples of metal–organic frameworks
exhibiting the flu topology.[13]
Space-filling diagrams of the structures of 1 and 2 suggest-
ed that evacuation of the guest and bound solvent molecules
could potentially give rise to microporous solids in both
cases. To test the porosity of the two materials, as-synthe-
sized samples were first soaked in distilled methanol to ex-
change high-boiling DMF from within the pores with a
lower-boiling solvent. We have previously shown that this
technique allows evacuation of a given framework at a re-
duced temperature, thus diminishing the possibility of col-
lapse upon guest removal.[2d] Despite this precautionary
step, desolvated samples of 1 did not retain crystallinity and
showed no significant gas uptake, suggesting that framework
collapse in this case occurs even under relatively mild evacu-
ation conditions. Indeed, although previous examples of tet-
razolate-bridged frameworks based on linear trimetallic
AHCTUNGRTENGUN(N ttpm)2·0.7CuCl2 (2d). As expected, X-ray analysis of an
evacuated single crystal of 2d revealed a further decrease of
the Clꢀ occupancy at the central position within the square-
planar {Cu4Cl}7+ units. Although partially occupied Clꢀ
anions are still bound to outside axial positions of Cu4 units
in 2d, X-ray analysis suggested that the Soxhlet extraction
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Structure and Charge Control in Metal–Organic Frameworks
FULL PAPER
eliminated the central Clꢀ anion from ca. 50% of the
{Cu4Cl}7+ clusters. Despite the fact that only a limited
amount of CuCl2 was eliminated from 2 under these condi-
tions, the transformation from 2 to 2d represents the first
example of a postsynthetic modification in which the charge
of the metal–organic framework is reduced.
tion amount of 640 cm3 gꢀ1 at 1 bar. Fits of the isotherm em-
ploying the BET and Langmuir models gave apparent sur-
face areas of 2506(2) and 2745(3) m2 gꢀ1, respectively. Signif-
icantly, these represent the highest surface areas yet report-
ed for a tetrazolate-bridged framework, surpassing the
previous record held by Ni2.75Mn0.25[(Mn4Cl)3(btt)8]2
Further evidence of CuCl2 elimination from 2 comes, as
one may expect, from the significant structural changes
caused by the loss of Clꢀ from the square-planar {Cu4Cl}7+
building units. In this context, the most significant changes
·20CH3OH, which exhibits
a
BET surface area of
2110(5) m2 gꢀ1 and
2282(8) m2 gꢀ1.[14]
a
Langmuir surface area of
The combination of high internal surface area and ex-
posed metal coordination sites suggested that compound 2d
might be of interest for hydrogen storage applications.
Indeed, its H2 adsorption isotherm at 77 K revealed a rever-
sible uptake of 2.8 wt% at 1.2 bar (Figure 4), representing
ꢀ
were observed in the length of the Cu N bonds and the
trans Cu···Cu distances, which were shortened from 2.036(3)
and 5.078(2) ꢁ, respectively, in 2, to 1.985(3) and
4.932(2) ꢁ, respectively, in 2d. However, despite a shorten-
ing of the distances within the square-planar units, which
are situated parallel to the ac plane, the a and c parameters
are in fact larger in 2d than in 2, as shown in Table 1. This
seemingly counterintuitive observation is due to a reorgani-
zation of the tetrahedral ligand, wherein the acute angle be-
tween two of the arms widens from 84(1) in 2 to 89(1)8 in
2d.
Table 1. Comparison of the tetragonal unit-cell dimensions for 2 and 2d.
2
2d
Difference ([%])
a [ꢁ]
c [ꢁ]
V [ꢁ3]
15.501
29.401
7064
16.091
28.187
7299
0.59 (3.8)
ꢀ1.214 (ꢀ4.1)
235 (3.3)
*
*
)
Figure 4. Isotherms for the excess uptake of H2 within 2d at 77 K (
,
As such, the a and c cell edges are extended, whereas the
b parameter is shortened for an overall cell volume augmen-
tation of 3.3% in going from 2 to 2d. In 2d, two types of
pores exist: tetragonally-distorted octahedral cagelike pores
defined by six {Cu4Cl}7+ units and eight ttpm4ꢀ ligands and
with interior atom-to-atom dimensions of 27.5ꢂ17.8ꢂ
17.8 ꢁ3, and rhombohedral-shaped two-dimensional chan-
nels running parallel to the ac plane, with diagonal atom-to-
atom dimensions of 14.1ꢂ12.6 ꢁ2.
~
,
~
and at 87 K (
). Filled and empty symbols represent adsorption and
desorption data, respectively, whereas the lines correspond to the virial
fits to the two adsorption isotherms.
one of the highest H2 uptakes reported for a metal–organic
framework under these conditions.[15] Measurement of an H2
adsorption isotherm at 87 K and fitting of the combined 77
and 87 K isotherms allowed calculation of the isosteric heat
of adsorption, which showed a zero-coverage value of
8.4 kJmolꢀ1. This is slightly lower than the value of
An N2 adsorption isotherm for 2d, shown in Figure 3, re-
vealed a reversible Type I adsorption isotherm with a satura-
9.4 kJmolꢀ1 established for HCu (btt)8]·3.5HCl.[11a]
ACHTNUTRGENN[UG (Cu4Cl)3ACHTUGNTRENNUGN
The lower zero-coverage enthalpy of adsorption in 2d is
likely a consequence of the reduction in the number of
strong H2 binding sites due to the presence of Clꢀ anions
and the fact that, as evidenced by X-ray crystallography,
only 70% of the Cu2+ sites are available for H2 binding,
with Clꢀ anions occupying the rest of the available sites. Fur-
ther H2 adsorption measurements at pressures up to 70 bar
revealed an excess H2 uptake of 4.1 wt% at 20 bar and
77 K, as shown in Figure 5. The total uptake of 5.6 wt% at
70 bar (corresponding to a volumetric H2 storage density of
41 gLꢀ1), is comparable to the total gravimetric uptakes of
Mn3CAHTNUGERTN[NUNG (Mn4Cl)3ACTUHNTGNNER(GUN btt)8ACHNUTRGTE(NUNNG CH3OH)10]2 and HCuAHTCUGNTERN[NUNG (Cu4Cl)3ACHTUNGTRENNUNG(btt)8]
·3.5HCl,[2d,11] which at 70 bar showed total uptakes of 6.7
Figure 3. Isotherm for the adsorption of N2 within 2d at 77 K.
and 5.6 wt%, respectively, but is lower than the total H2
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J. R. Long et al.
dilute HCl (ca. 50 mL, 1m) until no further precipitate formed. The pre-
cipitate was then collected by filtration, dried in air, and dissolved in
aqueous NaOH (1m). The resulting clear, colorless solution was titrated
with dilute HCl (ca. 20 mL, 1m) until the pH of the solution was 4. The
ensuing precipitate was washed with distilled water (3ꢂ150 mL) and
dried in air to afford 0.75 g (70%) of product as a white powder.
1H NMR ([D6]DMSO, 400 MHz): d=8.05 (d, 8H, J=8.8 Hz), 7.57 ppm
(d, 8H, J=8.8 Hz); 13C NMR (D6]DMSO, 400 MHz): d=131.7,
127.4 ppm (aromatic tertiary C); IR (neat): n˜ =3364 (m, br), 3215 (m,
br), 3105 (m, br), 3033 (m, br), 2941 (w, br), 2876 (m, br), 2775 (m, br),
1614 (s), 1568 (s), 1501 (vs), 1439 (s), 1250 (m), 1155 (m), 1074 (m), 1025
(w), 998 (m), 760 (m), 748 (s), 733 (s), 704 cmꢀ1 (s); elemental analysis
calcd (%) for C29H20N16·7H2O: C 48.46, H 4.77, N 31.18; found: C 48.66,
H 4.78, N 31.13.
Mn
G
(1):
Solid
Mn
G
(190 mg,
0.95 mmol) and H4ttpm·7H2O (50 mg, 0.070 mmol) were dissolved in a
mixture of DMF (10 mL) and methanol (8 mL) inside a 20 mL scintilla-
tion vial sealed with a Teflon-lined cap. The vial was heated at 758C for
4 d. Colorless cube-shaped crystals deposited on the walls of the vial
after ca. 2 d. The crystals were collected by filtration inside a nitrogen-
filled glove bag, quickly rinsed with 10 mL of anhydrous DMF, and then
soaked in distilled methanol. Upon evacuation at 858C, 40 mg (70%) of
product was obtained. IR (neat): n˜ =3162 (br, m), 2828 (m), 1616 (w),
1450 (s), 1423 (m), 1230 (w), 1119 (w), 1003 (vs), 833 (vs), 763 (s), 735
(s), 647 cmꢀ1 (vs); elemental analysis calcd (%) for C102H89Mn6N53O8: C
48.71, H 3.58, N 29.52; found: C 46.90, H 2.85, N 29.23; this compound is
water- and moisture-sensitive.
Figure 5. Isotherms for the adsorption of H2 within 2d at 77 K. Empty
and solid symbols represent excess and total uptake, respectively.
uptake of 9.4 wt% observed for Zn4O(1,4-benzenedicarbox-
ylate)3 under these conditions.[2g]
Conclusion
Cu
A
N
(2):
Solid
CuCl2·2H2O
(100 mg, 0.59 mmol) and H4ttpm·7H2O (50 mg, 0.070 mmol) were dis-
solved in a mixture of DMF (7 mL) and methanol (3 mL) inside a 20 mL
scintillation vial sealed with a Teflon-lined cap. The initially green sus-
pension dissolved upon addition of concentrated HCl (ca. 20 mL) to
afford a clear bright-green solution, which was left undisturbed at room
temperature for 4 d. Green tetragonal rodlike crystals were deposited on
the bottom and walls of the vial, and were collected by filtration inside a
nitrogen-filled glove bag and quickly rinsed with anhydrous DMF
(10 mL). After drying at 758C under reduced pressure, a yield of 39 mg
(61%) of product was isolated. IR (neat): n˜ =3035 (br, w), 1646 (s), 1607
(m), 1454 (vs), 1418 (m), 1369 (w), 1116 (w), 1062 (w), 1009 (m), 829
(vs), 759 (s), 739 (s), 695 cmꢀ1 (m); elemental analysis calcd (%) for
C131H121Cl4Cu10N69O16: C 42.58, H 3.30, N 26.16; found: C 42.66, H 2.88,
N 25.96; this compound is sparingly soluble in DMF, insoluble in nonpo-
lar organic solvents, and is water- and moisture-sensitive.
The foregoing results show that use of predesigned three-di-
mensional organic ligands can circumvent the formation of
low-dimensional systems, enabling isolation of metal–organ-
ic frameworks with rare, highly-connected three-dimensional
topologies. Herein, two contrasting examples serve to reiter-
ate that predicting the stability of any given framework to
desolvation remains a great challenge, but that targeting
three-dimensional systems by using this strategy can be an
effective way for discovering new materials with permanent
porosity. Future efforts will focus on further developing the
coordination chemistry of three-dimensional bridging li-
gands such as H4ttpm and its adamantane-centered ana-
logue. In addition, the unprecedented capability of the
{Cu4Cl}7+ tetrazolate clusters to eliminate chloride anions
will be explored in the context of sequestering small mole-
cules for potential applications in their storage, activation,
and catalytic transformation.
CuACTHNURGTENNUG(ttpm)2·0.7CuCl2 HCATUNGTRENN(UGN 2d): A freshly-prepared sample of 2 was loaded
into a Soxhlet extractor equipped with a water condenser. Freshly dis-
tilled methanol was heated to reflux and cycled through the sample for
5 d, during which it changed color to green. The methanol-washed crys-
tals were then dried by heating at 658C under high vacuum (<10ꢀ5 torr)
for 2 d. IR (neat): n˜ =3382 (br, w), 1614 (m), 1453 (vs), 1258 (w), 1162
(w), 1124 (w), 1072 (w), 1008 (s), 836 (s), 758 (m), 739 (m), 697 (w),
656 cmꢀ1
(w);
elemental
analysis
calcd
(%)
for
C58H32Cl1.4Cu4.7N32·5.5H2O: C 42.88, H 2.67, N 27.59; found: C 43.04, H
2.25, N 27.19.
Experimental Section
Gas adsorption measurements: Gas adsorption isotherms for pressures in
the range 0–1.2 bar were measured by using a Micromeritics ASAP2020
instrument. High pressure H2 adsorption isotherms were measured on a
HyEnergy PCTPro-2000 instrument in a manner that has been previously
described.[2d] Ultra-high purity He (UHP grade 5.0, 99.999% purity) was
used for free-space measurements. H2 and N2 isotherms at 77 K were
measured in liquid nitrogen baths by using UHP-grade gas sources. H2
isotherms at 87 K were measured in liquid argon baths. Oil-free vacuum
pumps and oil-free pressure regulators were used for all measurements
to prevent contamination of the samples during the evacuation process,
or of the feed gases during the isotherm measurement. The total amount
of hydrogen stored in 2d was calculated as previously described.[2d]
General: All reagents were obtained from commercial vendors and,
unless otherwise noted, were used without further purification. Methanol
was distilled over Mg/I2 prior to use. The compound tetra(p-cyanophe-
nyl)methane was synthesized according to a previously published proce-
dure.[7] Caution! Although we did not encounter any incident while han-
dling the compounds described herein, metal azides and tetrazoles are po-
tentially explosive and should be handled with great care.
Tetrakis(4-2H-tetrazol-5-yl-phenyl)methane
heptahydrate
(H4ttpm·7H2O): mixture of tetra(p-cyanophenyl)methane (0.62 g,
A
1.5 mmol), NaN3 (1.2 g, 18 mmol), and triethylamine hydrochloride
(2.5 g, 18 mmol) in toluene (25 mL) and methanol (5 mL) was heated at
reflux in a 100 mL round-bottomed flask for 4 d. Upon cooling to room
temperature, an aqueous solution of NaOH (25 mL, 1m) was added, and
the mixture was stirred for 30 min. The aqueous layer was treated with
X-ray structure determinations (see Table S1 in the Supporting Informa-
tion): Crystals of 1, 2, and 2d were coated in Paratone-N oil, attached to
Kapton loops, transferred to a Siemens SMART APEX diffractometer,
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Structure and Charge Control in Metal–Organic Frameworks
FULL PAPER
and cooled in a dinitrogen stream. Lattice parameters were initially de-
termined from a least-squares analysis of more than 100 centered reflec-
tions; these parameters were later refined against all data. None of the
crystals showed significant decay during data collection. The raw intensi-
ty data were converted (including corrections for background, Lorentz,
and polarization effects) to structure factor amplitudes and their esdꢃs by
using the SAINT 7.07b program. An empirical absorption correction was
applied to each data set by using SADABS. Space-group assignment was
based on systematic absences, E-statistics, and successful refinement of
the structures. Structures were solved by direct methods with the aid of
difference Fourier maps and were refined against all data by using the
SHELXTL 5.0 software package. Hydrogen atoms were inserted at ideal-
ized positions and refined by using a riding model with an isotropic ther-
mal parameter 1.2 times that of the attached carbon atom. To determine
the correct stoechiometry for 2 and 2d, the occupancies and thermal pa-
rameters of extraframework Cu and Cl atoms were refined freely. The
disorder evidenced in the electron-density map prevented the refinement
of solvent molecules within the pores of these three compounds. As such,
all peaks with electron densities larger than one electron were refined as
partially occupied oxygen and carbon atoms. The poor quality of the dif-
fraction data and extreme disorder of the bound and guest solvent mole-
cules led to relatively large R1 and wR2 values for the structure of 1.
However, the connectivity and structure of the skeleton within 1 was un-
equivocally determined by using this dataset. CCDC-690344, -690345,
and -690346 contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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Received: July 2, 2008
Published online: October 9, 2008
Chem. Eur. J. 2008, 14, 10280 – 10285
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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