Cocrystal controlled solid-state synthesis of a rigid tetracarboxylate ligand that pillars both square grid and Kagome lattice layers

Article abstract of DOI:10.1039/c0ce00542h

[Cu₂(carboxylate)₄] paddlewheel molecular building blocks, MBBs, are capable of generating square grid or Kagome lattice supramolecular isomers when dicarboxylates such as 1,3-benzenedicarboxylate (1,3-bdc) and 1,4-benzenedicarboxyla

Full text of DOI:10.1039/c0ce00542h

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Cocrystal controlled solid-state synthesis of a rigid tetracarboxylate ligand
ꢀ
that pillars both square grid and Kagome lattice layers†
*
Jason A. Perman, Amy J. Cairns, qukasz Wojtas, Mohamed Eddaoudi and Michael J. Zaworotko
Received 16th August 2010, Accepted 19th September 2010
DOI: 10.1039/c0ce00542h
a tetracarboxylic acid 5,50-(1,3,6,8-tetraoxobenzo[Imn][3,8] phenan-
throline-2-7-diyl)bis-1,3-benzenedicarboxylic acid, H4BIPA-TC, is
prepared using C3S3 and then used as a ligand to generate two
isomeric nets that represent examples of ‘‘ligand-to-ligand’’ pillaring.
The 120ꢀ angle subtended by the carboxylate moieties of 1,3-bdc
means that it can serve as an angular linker between the vertices of
[M2(carboxylate)4] paddlewheel MBBs and sustain squares of
[Cu2(carboxylate)4] paddlewheel molecular building blocks, MBBs,
ꢀ
are capable of generating square grid or Kagome lattice supramo-
lecular isomers when dicarboxylates such as 1,3-benzenedicarboxy-
late (1,3-bdc) and 1,4-benzenedicarboxylate (1,4-bdc) are exploited
to link the paddlewheel MBBs. In this contribution we demonstrate
that it is possible to use a solvent-free reaction (cocrystal controlled
solid-state synthesis) to prepare a tetracarboxylic acid, H4BIPA-
TC, formed by rigidly linking two 1,3-bdc moieties at the 5-position.
squares (that in turn form undulating square grids)24 or triangles of
25
squares (that in turn form Kagome lattices). 1,3-bdc can also
ꢀ
ꢀ
BIPA-TC can pillar both square grid and Kagome lattice supra-
generate structures with both triangles and squares, the combination
of which facilitates curvature and polyhedral structures that can exist
within infinite nets (e.g. supermolecular building blocks, SBBs, as in
HKUST-117 and rht-126) or as discrete molecules (e.g. small rhom-
bihexahedra, faceted polyhedra that represents prototypal metal–
organic polyhedra or nanoballs10,11) (Fig. 1). Rigidly linked pairs of
1,3-bdc ligands cannot link nanoballs because the only feasible 24-
connected net is binodal and requires a 3-connected node, e.g. a 24,3-
or rht topology.26–31 However, flexibly linked pairs of 1,3-bdc moieties
can engage in multiple links between the triangular or square
windows of nanoballs and thereby reduce the nanoball to an
8-connected or 6-connected node.32–34 Flexibly linked 1,3-bdc
molecular isomers, thereby generating nets that exhibit lvt or nbo
topologies, respectively.
The continually evolving field of crystal engineering applies the
concepts of supramolecular chemistry to facilitate bottom-up design
of crystal structures. That molecular level control can be exerted over
structure in turn affords diversity of composition and can even lead to
control over properties as exemplified by two classes of compound:
organic structures such as pharmaceutical cocrystals that enhance
solubility or stability of a pharmaceutically active ingredient;1 metal–
organic materials (MOMs) that use metals or metal clusters as
nodes and multi-functional organic ligands as linkers.2–9
Carboxylate sustained MOMs are particularly well studied and
have furnished a number of prototypal structures based upon 1,3-
bdc,10–12 1,4-bdc,13–15 and 1,3,5-benzenetricarboxylate.16,17 We have
been exploring green chemistry approaches for the synthesis of new
imide based ligands via condensation of anhydrides and amines in the
solid-state, i.e. cocrystal controlled solid-state synthesis (C3S3).18 C3S3
reactions are a subset of the much broader class of reactions
encompassed by solid-state synthesis and are distinguished by the
reactants that form in a cocrystal phase prior to reaction. Reduction
or complete elimination of solvent and direct isolation of a pure
product offers obvious advantages over solvent based approaches to
synthesis.19–23 In this contribution we demonstrate how
Department of Chemistry, University of South Florida, 4202 East Fowler
Avenue, CHE 205, Tampa, Florida, 33620-5250, USA. E-mail: xtal@
usf.edu; Tel: +1 813-974-3451
† Electronic supplementary information (ESI) available: FTIR, TGA,
and NMR information is available for the ligand synthesis; a list of
ꢀ
ligands used for pillaring Kagome lattice and square grids is given in
Fig. 1 [M2(carboxylate)4] moieties (squares) linked at their vertices by
Fig. S5. CCDC reference numbers 789422–789424. For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/c0ce00542h
1,3-bdc ligands can generate three supramolecular isomers: square grids,
ꢀ
Kagome layers or discrete nanoballs.
3130 | CrystEngComm, 2011, 13, 3130–3133
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HNO3 (0.45 mL, 3.5 M in DMF) was placed in a 20 mL scintillation
vial. The solution was heated at 1.5 ꢀC minꢁ1 to 85 ꢀC for 12 hours,
heated at 105 ꢀC for 23 hours and at 115 ꢀC for 23 hours, affording
single crystals of [Cu2(BIPA-TC)(H2O)2]n, 1 (ESI†).‡ The crystal
structure of 1 reveals that it is sustained by [Cu2(carboxylate)4] pad-
˚
dlewheel MBBs (Cu/Cu davg ¼ 2.636(4) A), the vertices of which are
ꢀ
linked into Kagome layers that are in turn pillared via ligand-to-
ligand cross-linking (Fig. 3). Compound 1 therefore exhibits two
types of 4-connected node (the paddlewheels and the BIPA-TC
ligands) and their connectivity generates nbo topology. There are two
types of windows and cavities in 1. One set of windows results from
triangles of square paddlewheels and exhibits an effective diameter of
˚
ca. 5.0 A. These windows lie above and below a cavity that results
from cross-linking the remaining six vertices of the triangles of square
Fig. 2 Powder XRD and materials listed from bottom to top
5-NH2BDC, NTCDA, dry grind, DMF grind (cocrystal), and
H4BIPA-TC.
paddlewheels by six BIPA-TC ligands. This cavity can accommodate
˚
an ꢂ12.1 A diameter sphere (Fig. S4†). The second cavity is con-
˚
nected through isosceles triangular windows with dimensions 12.25 A
˚
by 3.94 A (L ꢃ W). This small opening is due to the imide moiety
rotating 82.2ꢀ and 79.2ꢀ with respect to the isophthalate plane,
presumably because of steric repulsion between isophthalate C–H
and imide C]O moieties. This cavity spans two layers with a length
moieties can also facilitate variants on Kagome lattices.35 We herein
ꢀ
describe how a ligand based upon rigidly linked 1,3-bdc moieties can
be prepared using C3S3 and subsequently used to cross-link or pillar
either of the 2D nets that are based upon [M2(carboxylate)4]
paddlewheel MBBs.
˚
˚
of ꢂ32 A and it exhibits a diameter of ꢂ9 A at its widest point
(Fig. S4†). With axial ligands and solvent molecules removed,
1 exhibits 70% void space as calculated by Platon.37
A mixture of Cu(NO3)2$2.5H2O (0.052 mmol), H4BIPA-TC (0.05
mmol), DMA (1 mL), H2O (1 mL), and pyridine (0.1 mL, 1 M in
DMF) was placedina20 mLscintillationvial. The solutionwasheated
at 1.5 ꢀCminꢁ1 to 85 ꢀC for 12 hours, heated at 105 ꢀC for 23 hours and
at 115 ꢀC for 23 hours, affording single crystals of [Cu2(BIPA-
TC)(DMA)2]n, 2a (ESI†).‡ [Cu2(carboxylate)4] paddlewheels (Cu/
Experimental and results
Synthesis of H4BIPA-TC: 5-aminoisophthalic acid (5-NH2BDC) and
1,4,5,8-naphthalene tetracarboxylic dianhydride (NTCDA) were
ground in a pestle and mortar in 2 : 1 stoichiometry with 100 mL
DMF resulting in the formation of a purple cocrystal. The cocrystal
was heated for one hour at 180 ꢀC to afford yellow H4BIPA-TC in
yields of >95% (ESI†). Synthesis by refluxing in DMF has also been
accomplished with yields of 85%.36 Fig. 2 illustrates how this reaction
can be monitored using powder X-ray diffraction. Dry grinding of
the substrates affords a simple mixture of 5-NH2BDC and NTCDA.
Similar behavior was seen with NTCDA and 3-aminobenzoic acid.18
H4BIPA-TC is also isolated if the dry grind is heated. In both
instances the isolated product is largely amorphous.
˚
Cu d ¼ 2.6620(7) A) assemble into squares that adopt 1,2-alternate
calixarene-like partial cone conformations and render 4,4-nets that
˚
possess an ꢂ4.6 A diameter window. Layers are cross-linked through
˚
˚
BIPA-TC ligands, thereby generating zigzag channels of 10 A by 13 A
and an lvt topology (Fig. 3). An ssb-like topology could also result with
4,4-layers if the squares of paddlewheels had adopted 1,3-alternate
partial cone conformations, a situation which indeed occurred with
another rigid tetracarboxylate ligand.38 With axial ligands and solvent
molecules removed 2exhibits 66% void space ascalculatedbyPlaton.37
Cu(NO3)2$2.5H2O (0.1 mmol), H4BIPA-TC (0.05 mmol), DMF (1
A mixture of Cu(NO3)2$2.5H2O (0.15 mmol), as prepared
H4BIPA-TC (0.052 mmol), DMF (1 mL), chlorobenzene (1 mL) and
4ꢁ
ꢀ
Fig. 3 [Cu2(O2CR)4] linked by 1,3-bdc generates either Kagome (above) or square grid (below) layers which can then be cross-linked by BIPA-TC
.
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˚
˚
M ¼ 891.72, orthorhombic Imma; a ¼ 15.2248(3) A, b ¼ 36.4392(7) A,
mL), methanol (0.5 mL), 3,5-lutidine (11.3 mL), HMTA (100 mL, 1.4
MinH2O) and HNO3 (0.4 mL, 2.8 M in DMF) heated at 1.5 ꢀCminꢁ1
to 105 ꢀC for 24 hours afforded single crystals of [Cu2(BIPA-TC)(3,5-
lutidine)2]n,2b (ESI†).‡ Compound 2b is isostructural with 2a but
3,5-lutidine is coordinated to the paddlewheel moieties (Cu/
c ¼ 10.3036(2) A, V ¼ 5716.23(19) A , Z ¼ 4, Dcalcd ¼ 1.036 Mg mꢁ3, m ¼
1.352ꢁ1, GOF ¼ 1.032, final R1 ¼ 0.0375, wR2 ¼ 0.1018 [for 2594 data I >
2s(I)]. Crystal data for 2b at 183(2) K: Cu2C44H28N4O12, M ¼ 931.78,
3
˚
˚
˚
˚
˚
orthorhombic, Imma; a ¼ 14.981(21) A, b ¼ 36.371(5) A, c ¼ 10.922(2) A,
V ¼ 5951.1(16) A , Z ¼ 4, Dcalcd ¼ 1.040 Mg mꢁ3, m ¼ 0.763 mmꢁ1
,
3
˚
GOF ¼ 1.039, final R1 ¼ 0.0429, wR2 ¼ 0.1238 [for 2922 data I > 2s(I)].
˚
Cu d ¼ 2.6780(7) A).
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[Cu2(BIPA-TC)$solvent]n exhibits supramolecular isomers that can
be controlled by utilizing the appropriate conditions for their
synthesis. The isostructural series NOTT-100 through 108, 110, 111
and PCN-14, 46 were also constructed through ligand-to-ligand
cross-linking of 1,3-bdc moieties and exhibit the same topology as 1
whereas NOTT-109 exhibits ssb topology similar to 2. The NOTT
and PCN nets use benzene, naphthalene, substituted benzene, and
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ꢀ
bdc ligands had therefore afforded pillared Kagome (nbo) nets with
just one exception, NOTT-109. We herein report the first examples
ꢀ
of ligand-to-ligand pillared square grid and Kagome lattice struc-
tures which exhibit the same composition, i.e. supramolecular
isomers. Very recently, Kitagawa et al. reported that metal-to-
metal pillaring using diamine pillars and [Zn2(carboxylate)4] pad-
dlewheel MBBs can also afford such supramolecular isomers.42
The NOTT series of compounds were evaluated in terms of
porosity towards hydrogen and it was observed that smaller pore
volume and smaller surface area afforded higher Qst at low
loading. PCN-46 was also studied in terms of porosity towards
hydrogen and was found to exhibit a higher Qst at low loading
than NOTT-101, a compound with similar surface area.38,39
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Conclusions
There is not yet a set of general rules that defines how subtle changes
in reaction conditions afford one supramolecular isomer over another
but herein we demonstrate that it is at least possible to exert control
through reaction conditions. MOMs that are of the same composi-
tion but different in topology are not yet common but they could be
of fundamental value since they will facilitate systematic study of
binding affinity towards important guests such as small gas molecules
(especially hydrogen and carbon dioxide). In particular, they will
allow ‘‘apples with apples’’ comparisons of how pore size and surface
area affect guest binding energies. Preliminary experiments suggest
that 2a and 2b retain porosity following evacuation and in-depth
studies are underway to determine its uptake behavior towards
hydrogen and carbon dioxide. The synthesis of H4BIPA-TC reported
herein requires little or no solvent and affords a product that is ready
to use without cleanup. Such ligands might become attractive if and
when practical applications for MOMs are developed.
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Acknowledgements
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We gratefully acknowledge the financial support of the DOE-BES
(DE0FG02-07ER4670).
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‡ Crystal data for 1 at 100(2) K: Cu2C30H10N2O14, M ¼ 749.48,
˚
˚
˚
monoclinic, C2/m; a ¼ 32.461(12) A, b ¼ 18.024(6) A, c ¼ 19.748(7) A,
ꢀ
3
b ¼ 119.964(9) , V ¼ 10 010(6) A , Z ¼ 6, Dcalcd ¼ 0.746 Mg mꢁ3, m ¼
˚
0.672 mmꢁ1, GOF ¼ 0.951, final R1 ¼ 0.0819, wR2 ¼ 0.1424 [for 5453
data I > 2s(I)]. Crystal data for 2a at 100(2) K: Cu2C38H28N4O14
,
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