Cubic octanuclear Ni(II) clusters in highly porous polypyrazolyl-based materials

Article abstract of DOI:10.1021/ja102862j

Two highly porous coordination polymers, containing rare octanuclear hydroxo-nickel clusters and long bis-pyrazolyl spacers, are shown to possess, after mild thermal treatment, lattice cavities up to 72% of the total crystal volume.

Full text of DOI:10.1021/ja102862j

Published on Web 05/20/2010
Cubic Octanuclear Ni(II) Clusters in Highly Porous Polypyrazolyl-Based
Materials
†
,†
†
†
†
Norberto Masciocchi, Simona Galli,* Valentina Colombo, Angelo Maspero, Giovanni Palmisano,
‡
‡
,‡
Behnam Seyyedi, Carlo Lamberti, and Silvia Bordiga*
Dipartimento di Scienze Chimiche e Ambientali, UniVersit a` dell’Insubria, Via Valleggio 11, I-22100 Como,
Italy and Department of Chemistry IFM & NIS Centre of Excellence, UniVersity of Turin,
Via Quarello 11, I-10135 Torino
Received April 6, 2010; E-mail: simona.galli@uninsubria.it
Over the past two decades, many efforts have been devoted to
devise hybrid three-dimensional porous systems, in which metallic
isolation of the ꢀ-dicarbonyl intermediate. In contrast, species 2
was prepared by reacting 4-aminopyrazole with pyromellitic
anhydride in a one-pot reaction. These highly insoluble species
could be recovered as polycrystalline materials, the structure of
1
nodes are linked by long organic spacers, aiming at the formation
2
of thermally stable and chemically inert materials for gas storage,
2
0
gas separation, and catalytic purposes. To this goal, polycarboxy-
which was retrieved by X-ray powder diffraction (XRPD) data.
Both of these rod-like molecules crystallize in the P2 /c space group,
3
4
lates and, later, polyazolates have been largely employed, reaching
significant scientific and technological achievements, with some
of the best performing materials being marketed by leading chemical
1
within rather elongated cells, in which evident N-H· · ·N interac-
tions among neighboring molecules generate corrugated two-
dimensional sheets of fishbone aspect, well separated from adjacent
ones. Details of syntheses, spectroscopic properties, and structures
are supplied in the Supporting Information (SI).
5
companies.
The versatility of these systems can be traced back to the variety
of the metallic nodes (either simple ions or polymetallic oxo-
clusters), of the organic linkers, of the different synthetic techniques,
and to the possibility of generating polymorphic species depending
on the reaction or on the environmental conditions. Altogether,
On reacting 1 and 2 with Ni(OAc) ·4H O in a variety of solvents,
2
2
two polycrystalline derivatives, [Ni (OH) (OH ) (pbp) ]·nSolv and
8
4
2 2
6
[Ni (OH) (OH ) (tet) ]·nSolv (3 and 4, respectively) were iso-
8
4
2 2
6
6
21
thousands of species of this kind have appeared in the literature:
lated. Their XRPD structural analysis showed that these two
isomorphous species are constituted by octanuclear Ni(II) hydroxo
22
while some have been serendipitously isolated, several highly
performing materials were engineered using (poly)metallic nodes
clusters linked by tetradentate µ -pbp and µ -tet ligands in a complex
4
4
7
with specific geometric requirements, ligands of tailored coordina-
Ni (µ -X) (µ -L) polyhedron of rigorous cubic symmetry (X )
8
4
6
4
6
-
tion capacity, and, particularly, the highly fruitful isoreticular
OH or H O; L ) pbp or tet). Figure 1 shows the local
2
8
9
approach. In this respect, the polycarboxylate species of Yaghi
stereochemistry of the octametallic node, which closely resembles
1
0
11
23
2-
and F e´ rey, as well as the polyazolate materials reported by Long,
are widely considered renowned cornerstones of this field.
that of the recently reported [Ni (OH) (µ -pyrazolate) ] anion.
8
6
2
12
Similarly to the latter species, each Ni(II) ion in 3 and 4 is
In past years we have been interested in the coordination
chemistry of homoleptic metal pyrazolates, imidazolates, and
pyrimidinolates, which have demonstrated an extreme structural
hexacoordinated in a fac-NiN O fashion and shows intermetallic
nonbonding distances close to 3.0 Å (2.96-3.00 Å in ref 23).
In 3 and 4, the presence of long and rigid bis(exobidentate)
3
3
1
2
1
3
versatility, witnessed by the existence of cyclic oligomeric species,
spacers possessing pyrazolato moieties at both ends induces the
1
4
15
stretched and helical 1D polymers, layered compounds, and
dense, as well as porous, 3D frameworks. After shifting our
interests toward polytopic nitrogen ligands containing several donor
sites, we have eventually prepared two new bis-pyrazolyl species,
,4′-bis(1H-pyrazol-4-yl)biphenyl, 1, H pbp, and 2,6-bis(1H-pyra-
zol-4-yl)pyrrolo[3,4-f]isoindole-1,3,5,7(2H,6H)-tetrone, H tet (Chart
), in which the heterocycles are separated by long rigid spacers.
12+
formation of a fcc packing of the [Ni
linked to 12 symmetry-related nodes by the µ
8
(µ
4
-X)
6
]
clusters, each
1
6
-L2- ligands and
4
maintained more than 17 Å apart (see Figure 1). As recently
encountered in Zr (OH) (L*) (L* ) linear polyphenylendicar-
17
6
O
4
4
6
2
4
2
boxylates), this favorable topology and coordination geometry
result in highly porous 3D frameworks: indeed, upon elimination
of the residual solvents from the as-prepared samples, they possess
accessible octahedral cavities (ca. 72% void volume in 3, ca. 70%
in 4) and, consequently, very low crystal density (down to less than
2
1
Chart 1. Molecular Drawings of Species 1 and 2
-
3
0
.50 g cm ). Therefore, these materials are ideal candidates for
gas sorption investigations. As a matter of fact, they show high N
sorption capacities, with Langmuir surface areas peaking well above
2
2
-1
1
700 m g . Notably, the occurrence and stability of these self-
assembled octanuclear Ni(II) SBUs in the presence of different
pyrazolato-based ligands can be fruitfully used in constructing finely
tuned, isoreticular porous coordination polymers with even longer,
or differently functionalized, spacers.
The preparation of 1 strictly followed the synthetic route reported
1
7
11,18
by us and others
yl)benzene: 1 was recovered in analytically pure form starting from
for the isolation of 4,4′-bis(1H-pyrazol-4-
A special comment is deserved by the still ambiguous formulation
set above for compounds 3 and 4, due to structural disorder. While
it is fairly obvious that solvent molecules can occupy the large voids
of the structure (trapped either during direct precipitation, subse-
1
,1′-biphenyl-4,4′-bis(acetic acid), through the Vilsmeier-Haack
19
reaction followed by heterocyclization with hydrazine, without
†
Universit a` dell’Insubria.
University of Turin.
‡
25
quent washing or from aerial moisture), it proved much more
7
902 9 J. AM. CHEM. SOC. 2010, 132, 7902–7904
10.1021/ja102862j  2010 American Chemical Society

C O M M U N I C A T I O N S
The XANES spectrum of 4 (Figure 3a) is very similar to that
2
8
observed for the Ni-CPO-27 MOF, confirming that in 4 (pseu-
do)octahedral Ni(II) ions are present, discarding, at the same time,
the presence of mixed-valence Ni(II)/Ni(III) clusters. More in detail,
three main transitions can be observed: a very weak 1sf3d dipole-
forbidden electronic transition at 8333.3 eV; a strong 1sf4p dipole-
allowed one near 8343 eV (scarcely visible because too close to
the edge jump); and a white line at 8349.5 eV (first resonance after
the edge). Worthy of note, the higher intensity of the 1sf3d
transition observed in 4 with respect to that observed in the Ni-
8 4 6 4 6
Figure 1. Left: drawing of the Ni (µ -X) (µ -L) cluster (X ) hydroxyl or
water fragments) in 3 and 4. Dashed lines are a guide to the eyes highlighting
the octametallic cube. For simplicity, all X ligands are idealized as hydroxyl
groups. Right: drawing of the crystal packing in 4, showing, with yellow
solid spheres, the location (neither the sizes nor the shapes) of the cavities
CPO-27 MOF reflects a higher distortion from a perfect local O
symmetry: in 4 the NiN chromophore is present, while in Ni-
h
3 3
O
CPO-27 six (chemically unequivalent) oxygen atoms are bound to
Ni(II); see SI for direct comparison.
oc rb yt as ti an le dv o ul up mo ne.mild evacuation of the solid, accounting for ∼70% of the
2,28
As was the case for other MOF systems,
notwithstanding the
knowledge of the structure from XRPD, EXAFS data interpretation
was not straightforward (see SI). Indeed, several single and multiple
scattering (SS and MS) paths contribute to the overall amplitude.
Contributions of the SS paths N1 (joint with O1), N2, Ni1, and
Ni2, as can be singled out in Figure 3c, are highlighted as colored
traces in Figure 3b in k-space. The final results of the structural
refinement are shown in Table 1: the experimental geometrical
parameters derived from our combined EXAFS and XRPD data
analysis confirm the powder X-ray structure presented above, ruling
difficult to assess the real nature of the X ligands, which we model
-
2
as a 2:1 ratio of OH and H O moieties. As a matter of fact, species
3
and 4 contain octanuclear clusters similar to those found in
2
6
[
Ni
were found to belong to water, rather than hydroxo, ligands,
statistically distributed on the surface of the Ni cube. Aiming at
8
(OH)
4
(H
2
O)
2
(C
5
H
9
O
2
)
12], where two of the six µ
4
-O atoms
8
the full comprehension of the nature of 3 and 4, we have chosen
the latter as a representative example to perform a number of
complex spectroscopic analyses. The DRS-UV-vis spectrum of
2
8
out the presence of extraframework nickel-containing cations,
]2-
balancing metallic nodes of a much simpler [Ni
formulation.
8
(OH)
6 4 6
(µ -L)
4
(blue curve in Figure 2a) shows electronic transitions associated
with the organic linker 2 (three strong bands peaking at 34 500,
-
1
2
9 500, and 22 300 cm , gray curve) and two weaker d-d
-1
transitions for pseudo octahedral Ni(II) ions (15 900, 10 200 cm ).
The latter are perturbed upon water removal (Figure 2a) testifying
a distortion of the Ni(II) coordination sphere. The IR spectra of
the as-prepared sample and those obtained upon its activation at
increasing temperatures, up to 453 K, are shown in Figure 2b.
Beyond the expected bands due to the linker (lying in the
3
160-2850 and 1790-500 cm-1 ranges; see SI for the latter),
progressive elimination of water is observed with a sharpening of
the absorption band at 3593 cm , attributed to the bridging OH
groups located on the faces of Ni units. Worthy of note, this band
lies at a significantly lower frequency than that observed for the
hydroxyl groups in Ni-phosphonates, likely because of the unusual
-bridging mode of the hydroxyl moieties in 4. Notably, the
persistence of a band centered at 3370 cm , eVen after prolonged
outgassing at 453 K, can only be explained by considering the
presence of structural water molecules that cannot be remoVed
without compromising the MOF structure. These assignments are
-1
8
27
Figure 3. XANES spectrum for species 4 (a). Results of the EXAFS
analysis for species 4 in k-space (b), reporting the most important SS
contributions defined from the cluster shown in (c), where A ) adsorber.
µ
4
-1
The possible presence of other extraframework cationic moieties
was thoroughly tested and coherently discarded, by coupling
elemental analyses as well as chemical and unconventional
2
confirmed by IR spectroscopy, namely D O-induced proton ex-
change and (low temperature) framework interaction with CO (see
SI for further details).
spectroscopic evidence (see SI): the presence of protonated cations
+
of the H
3
L type could be ruled out through vibrational spectros-
copy, elemental analysis, and in view of the basic environment in
which the syntheses were performed. We are thus left with the final
formulation of species 3 and 4 as [Ni
8
(OH)
4
(OH
2
)
2
(µ
4
-L)
6 2
]·nH O,
eventually clearing out the ambiguity put forward in the previous
text.
The thermal stability of these coordination polymers has been
investigated by DSC/TG and, particularly, by thermodiffractometric
analyses. As shown in Figure 4, compound 4 is stable from rt (blue
trace) up to 410 °C, where decomposition begins. In this temperature
range, variable temperature X-ray powder diffraction data indicate
a substantial constancy of the crystal structure, with only marginal
changes of some low-angle peak intensity, due to water elimination.
This process is reversible: in open air, moisture is readsorbed in a
few hours.
Figure 2. Effect of successive outgassing (see legend) on UV-vis (a) and
IR spectra (b) of 4. Also the spectrum of 2 is reported in (a). K-M u. )
Kubelka-Munk units; a.u. ) absorbance units.
J. AM. CHEM. SOC. 9 VOL. 132, NO. 23, 2010 7903

C O M M U N I C A T I O N S
Table 1. Summary of EXAFS30 and XRPD Results; Esd’s in
Navarro, J. A. R. Chem. Mater. 2010, 22, 1664–1672, and references
Parentheses
therein.
(
5) Czaja, A. U.; Trukhan, N.; M u¨ ller, U. Chem. Soc. ReV. 2009, 38, 1284–
Parameter
EXAFS (4)
XRPD (3)
XRPD (4)
1293.
(
6) Long, J. R.; Yaghi, O. M. Chem. Soc. ReV. 2009, 38, 1213–1214.
R-factor
0.011
a
a
(7) Tranchemontagne, D. J.; Mendoza-Cort e´ s, J. L.; O’Keeffe, M.; Yaghi, O. M.
Chem. Soc. ReV. 2009, 38, 1257–1283.
∆
0
E
0, eV
-4.1(5)
0.92(4)
2.04(1)
0.0087(5)
2.77(2)
0.010(2)
2.96(1)
0.011(1)
4.12(3)
0.010(3)
-0.03(3)
0.007(1)
-
-
2
(8) Eddaoudi, M.; Kim, J.; Rosi, N.; Vodak, D.; Wachter, J.; O’Keeffe, M.;
Yaghi, O. M. Science 2002, 295, 469–472.
S
-
-
〈
R
O1,N1〉, Å
2.09-2.15
-
2.89
-
2.92
-
4.13
-
-
-
2.01-2.08
-
2.88
-
2.83
-
4.08
-
-
-
(
9) Eddaoudi, M.; Moler, D.; Li, H.; Reineke, T. M.; O’Keeffe, M.; Yaghi,
2
2
σ (O1,N1), Å
O. M. Acc. Chem. Res. 2001, 34, 319–330, and references therein.
R
N2, Å
(10) F e´ rey, G.; Serre, C. Chem. Soc. ReV. 2009, 38, 1380–1399, and references
2
2
σ (N2), Å
R
σ (Ni1), Å
R
therein.
(
11) Choi, H. J.; Dinca, M.; Long, J. R. J. Am. Chem. Soc. 2008, 130, 7848–
Ni1, Å
2
2
7850.
(
(
12) Masciocchi, N.; Galli, S.; Sironi, A. Comm. Inorg. Chem. 2005, 26, 1–37.
13) Masciocchi, N.; Corradi, E.; Moret, M.; Ardizzoia, G. A.; Maspero, A.;
La Monica, G.; Sironi, A. Inorg. Chem. 1997, 36, 5648–5650.
14) Masciocchi, N.; Moret, M.; Cairati, P.; Sironi, A.; Ardizzoia, G. A.; La
Monica, G. J. Am. Chem. Soc. 1994, 116, 7668–7676.
Ni2, Å
2
2
σ (Ni2), Å
(
(
R(all other paths)
2
2
σ (all other paths), Å
15) Ardizzoia, G. A.; La Monica, G.; Masciocchi, N.; Maspero, A.; Sironi, A.
Angew. Chem., Int. Ed. 1998, 37, 3366–3369.
a
See crystal data in ref 22.
(16) Galli, S.; Masciocchi, N.; Tagliabue, G.; Sironi, A.; Navarro, J. A. R.; Salas,
J. M.; Mendez-Li n˜ an, L.; Domingo, M.; Perez-Mendoza, M.; Barea, E.
Chem.sEur. J. 2008, 14, 9890–9901, and references therein.
(
17) Maspero, A.; Galli, S.; Masciocchi, N.; Palmisano, G. Chem. Lett. 2008,
3
7, 956–957.
(
(
(
18) He, X.; An, B.-L.; Li, M.-X. Acta Crystallogr. 2008, E64–o40.
19) Vilsmeier, A.; Haack, A. Ber. 1927, 60, 119.
14 4 1
20) Crystal data for 1: C18H N /c, a
, fw ) 286.34 g mol-1, monoclinic, P2
)
16.042(2) Å, b ) 5.5181(6) Å, c ) 7.8621(7) Å, ꢀ ) 93.96(1)°, V )
3 -3 -1
6
94.3(1) Å , Z ) 2, F ) 1.370 g cm , µ(Cu KR) ) 67.1 mm , R
and RBragg ) 0.035, 0.048, 0.015, respectively, for 3501 data collected in
the 5.0°-75.0° 2Θ range. Crystal data for 2: C16 , fw 348.28 g
/c, a ) 5.2503(4) Å, b ) 5.3608(3) Å, c ) 24.376(2)
p
, Rwp,
8 6 4
H N O
-1
mol , monoclinic, P2
Å, ꢀ ) 90.480(4)°, V ) 686.0(1) Å , Z ) 2, F ) 1.686 g cm , µ(Cu KR)
1
3
-3
1
)
108.3 mm- , R
001 data collected in the 5.0°-105.0° 2Θ range.
21) If, instead, NiCl · 6H O is reacted with H tet, a different species,
NiCl (H tet)] (5), is formed, structurally characterized by XRPD analysis
as containing 2D layers built upon pseudooctahedral trans-NiCl
chromophores linked in infinite NiCl ribbons. Crystal data for 5:
p
, Rwp, and RBragg ) 0.075, 0.104, 0.058, respectively, for
5
(
(
2
2
2
[
2
2
4
N
2
Figure 4. Thermodiffractogram of species 4, highlighting the substantial
constancy of its XRPD pattern, when heated, in air, from rt (blue trace) to
2
-1
j
2 6 4
N NiO , fw ) 477.88 g mol , triclinic, P1, a ) 6.315(1) Å, b )
C
16
H
8
Cl
3
.620(1) Å, c ) 18.443(3) Å, R ) 94.85(3)°, ꢀ ) 109.93(1)°, γ ) 89.25(3)°,
4
10 °C. The upper insert shows the relative changes of peak intensities
3
-3
-1
V ) 394.5(2) Å , Z ) 1, F ) 2.012 g cm , µ(Cu KR) ) 531.9 mm , R
p
,
due to extraframework water elimination.
R
wp, and RBragg ) 0.025, 0.036, 0.023, respectively, for 3525 data collected
in the 4.5°-75.0° 2Θ range. Differently, the reaction of H
2
pbp with
In summary, state-of-the-art structural powder diffraction tech-
2 2
NiCl · 6H O affords 4, i.e., the same product obtained with nickel acetate.
22) Crystal data for 3, [Ni
8
(OH)
4
(OH
2
)
2
(µ
4 6 80 8 6
-pbp) ], C108H N24Ni O , fw )
3
niques (which have recently increased the basket of structural tools
-1
j
2
279.53 g mol , cubic, Fm3m, a ) 31.358(3) Å, V ) 30836(9) Å , Z )
2
9
-3
-1
in the structural chemist’s hands, well beyond the traditional
methods of qualitative and quantitative analyses) were coupled with
X-ray absorption techniques and spectroscopic measurements,
allowing the detection and confirmation of relevant stereochemical
features and, above all, the determination of the correct, but elusiVe,
4, F ) 0.49 g cm , µ(Cu KR) ) 69.8 mm , R
.012, 0.008, for 3626 data collected in the 7.5°-80.0° 2Θ range. Crystal
data for 4: [Ni (OH) (OH (µ -tet) ]·6H 36, fw ) 2759.27
p
, Rwp, and RBragg ) 0.007,
0
8
4
j
)
2 2
4
6
2 56 8
O, C96H N36Ni O
-1
3
g mol , cubic, Fm3m, a ) 30.5845(2) Å, V ) 28610(6) Å , Z ) 4, F )
-3
-1
0
p
.64 g cm , µ(Cu KR) ) 89.4 mm , R , Rwp, and RBragg ) 0.030, 0.054,
0
.054, for 4876 data collected in the 7.5°-105.0° 2Θ range.
(23) Xu, J.-Y.; Qiao, X.; Song, H.-B.; Yan, S. P.; Liao, D.-Z.; Gao, S.; Journaux,
Y.; Cano, J. Chem. Commun. 2008, 6414–6416.
stoichiometry of these [Ni
8
(OH)
4
(OH
2
)
2
(µ
4
-L)
6
2
] · nH O porous
(
24) The presence of (disordered) solvent is witnessed by the fact that framework
atoms alone did not model the whole X-ray scattered intensity. The less-
than-ideal quality of the XRPD traces hampered solvent modeling.
coordination polymers.
Acknowledgment. Fondazione CARIPLO (Project No. 2007-
(25) Ovcharenko, V.; Fursova, E.; Romanenko, G.; Eremenko, I.; Tretyakov,
E.; Ikorskii, V. Inorg. Chem. 2006, 45, 5338–5350.
5
117) is heartily acknowledged for funding. Mr. Iacopo Galli, for
(
26) Miller, S. R.; Pearce, G. M.; Wright, P. A.; Bonino, F.; Chavan, S.; Bordiga,
S.; Margiolaki, I.; Guillou, N.; F e´ rey, G.; Bourrelly, S.; Llewellyn, P. L.
J. Am. Chem. Soc. 2008, 130, 15967–15981.
helping in the syntheses, and Dr. Damiano Monticelli, for helping
in ICP-MS analyses, are also acknowledged. XANES and EXAFS
(
27) (a) Bonino, F.; Chavan, S.; Vitillo, J. G.; Groppo, E.; Agostini, G.; Lamberti,
C.; Dietzel, P. D. C.; Prestipino, C.; Bordiga, S. Chem. Mater. 2008, 20,
3
0
spectra were collected at BM26A at ESRF.
4957–4968. (b) Chavan, S.; Vitillo, J. G.; Groppo, E.; Bonino, F.; Lamberti,
C.; Dietzel, P. D. C.; Bordiga, S. J. Phys. Chem. C 2009, 113, 3292–3299.
c) Chavan, S.; Bonino, F.; Vitillo, J. G.; Groppo, E.; Lamberti, C.; Dietzel,
P. D. C.; Zecchina, A.; Bordiga, S. Phys. Chem. Chem. Phys. 2009, 11,
811–9822.
Supporting Information Available: Details on the synthesis,
spectroscopy, crystallographic analysis (CIF files and Rietveld refine-
ment plots) of species 1-5; TG and DSC plots for species 1-4. Details
on the XANES and EXAFS data acquisition and analysis. EXAFS fit
in R-space. Details on the IR and DRS-UV-vis analyses; IR spectra
(
9
(
28) Hafizovic, J.; Bjorgen, M.; Olsbye, U.; Dietzel, P. D. C.; Bordiga, S.;
Prestipino, C.; Lamberti, C.; Lillerud, K. P. J. Am. Chem. Soc. 2007, 129,
3612–3620.
-
1
(29) David, W. I. F., Shankland, K., McCusker, L. B.; B a¨ rlocher, Ch., Eds.;
down to 50 cm . This material is available free of charge via the
Internet at http://pubs.acs.org.
Structure determination from powder diffraction data; Oxford University
Press: 2006, Oxford, U.K.
3
(
30) The fit was performed in R-space in the 1.0-4.5 Å range over k -weighted
-1
FT of the ꢁ(k) functions performed in the 2.0-16.0 Å interval. A single
2
References
0 0
∆E and a single S have been optimized for all SS and MS paths. The
Ni-O and Ni-Ni (first and second neighbor) SS paths have been modeled
2
(
(
(
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with their own path length and Debye-Waller factors, while a unique σ
and a unique path length parameter R, common to all other SS and MS
paths, have been optimized.
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JA102862J
7
904 J. AM. CHEM. SOC. 9 VOL. 132, NO. 23, 2010