Metal-organic frameworks incorporating Cu3(μ3-OH) clusters

Article abstract of DOI:10.1039/b604804h

Interaction of 4,4′-bi(1,2,4-triazole) (btr) with copper(II) chloride (bromide) in aqueous or aqueous alcohol media led to a series of coordination polymers featuring the formation of μ ₃-hydroxotricopper(II) clusters and their integration into 3D frameworks. These unprecedented structures originate in the propagation of trigonal hydroxotricopper(II) clusters bridged by tri- or tetradentate organic ligands. Complex [{Cu₃(μ₃-OH)}{Cu₃(μ ₃-O)}(μ₄-btr)₃(H₂O) ₄(OH)₂Cl₆]Cl·0.5H₂O adopts a structure of SrSi₂ topology, with eight-fold interpenetration of the coordination frameworks. The structure of [{Cu₃(μ ₃-OH)}₂(μ₃-btr)₆(μ ₄-btr)(μ-X)X₄]X₅·nH₂O (X = Br, n = 6; X = Cl, n = 8) involves 2D coordination layers [{Cu ₃(μ₃-OH)}(μ₃-btr)₃] _n with an exceptional (3,6)-net topology, which are cross-linked by tetradentate btr ligands and bridging chloride (bromide) ions. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b604804h

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PAPER
www.rsc.org/dalton | Dalton Transactions
Metal–organic frameworks incorporating Cu3(l3-OH) clusters†‡
Andrey B. Lysenko,a Evgen V. Govor,a Harald Krautscheidb and Konstantin V. Domasevitch*a
Received 3rd April 2006, Accepted 26th May 2006
First published as an Advance Article on the web 7th June 2006
DOI: 10.1039/b604804h
Interaction of 4,4ꢀ-bi(1,2,4-triazole) (btr) with copper(II) chloride (bromide) in aqueous or
aqueous alcohol media led to a series of coordination polymers featuring the formation of
l3-hydroxotricopper(II) clusters and their integration into 3D frameworks. These unprecedented
structures originate in the propagation of trigonal hydroxotricopper(II) clusters bridged by tri- or
tetradentate organic ligands. Complex [{Cu3(l3-OH)}{Cu3(l3-O)}(l4-btr)3(H2O)4(OH)2Cl6]Cl·0.5H2O
adopts a structure of SrSi2 topology, with eight-fold interpenetration of the coordination frameworks.
The structure of [{Cu3(l3-OH)}2(l3-btr)6(l4-btr)(l-X)X4]X5·nH2O (X = Br, n = 6; X = Cl, n = 8)
involves 2D coordination layers [{Cu3(l3-OH)}(l3-btr)3]n with an exceptional (3,6)-net topology, which
are cross-linked by tetradentate btr ligands and bridging chloride (bromide) ions.
allows the generation of the polymer by propagation of the trigonal
Introduction
geometry of the molecular unit (Scheme 1). In this case the twisted
conformation of the bitriazole11 facilitates control over the entire
connectivity: it predetermines an orthogonal orientation for the
successively bridged tricopper clusters and generation of a 3D
three-connected net.
In recent years, metal–organic frameworks1 containing coor-
dinatively unsaturated metal centers have received significant
attention2 due to the possibility of evaluating a fundamental
host–guest interaction, to perform chemical sensing, hydrogen
storage3 and catalysis.4 Increases in efficiency and selectivity of
such 3D host lattices may arise via the use of receptor centers,
in which the coordination core provides multiple binding sites,
as may be compared with simpler axially unsaturated copper(II)
diketonates, porphyrins and related systems.5 However, in most
polynuclear species the metal centers are blocked by ligation (as
occurs for l4-oxo zinc carboxylates) and therefore are almost
excluded from direct interaction with potential substrates.6 Unlike
these species, nearly planar l3-hydroxo trimetallic clusters retain
steric accessibility of the multiple metal centers at two axial
sides, they display potential in catalysis and in biology (e.g.,
reactions provided by copper blue oxidases)7 and they could be
best applied to the functionalization of metal–organic polymers.
Herein, we report the utilisation of this coordination archetype
as an unprecedented secondary building block5,8 for the pre-
programmed synthesis of framework solids.
Results and discussion
An efficient design strategy was based upon the construction of the
2
l3-hydroxotrimetallic core using suitable g -heterocyclic bridges
that also provide further integration of the cluster in a framework.
A series of molecular tricopper(II) clusters with 1,2,4-triazoles9
and pyrazolide ions10 supply a paradigmatic precedent for such
a combination of inorganic and organic bridges, while a doubled
functionality, as provided by the 4,4ꢀ-bi(1,2,4-triazole) ligand (btr),
Scheme 1 The l3-hydroxo cluster formed by btr ligands and cop-
per(II) chloride or bromide (a) and target polymeric motifs that imply
self-association (b) or further aggregation (c) of the tricopper clusters.
The framework structure of [{Cu3(l3-OH)}{Cu3(l3-O)}(l4-
btr)3(H2O)4(OH)2Cl6]Cl·0.5H2O (1) originates in a combination
of these design prerequisites, it exists in the form of a regular 3D
net of (10,3)-a topology (usually related to the SrSi2 structure;
103 tile) that implies the tricopper clusters are three-connected
nodes (Fig. 1, 2). This array may be best compared with a
hydrogen bonded framework formed by 4,4ꢀ-bipyrazole, in which
the pyrazole functions adopt a characteristic trimeric pattern.12
aInorganic Chemistry Department, Kiev University, Volodimirska Street 64,
Kiev, 01033, Ukraine. E-mail: dk@univ.kiev.ua
bInstitut fu¨r Anorganische Chemie, Universita¨t Leipzig, Linne´straße 3, D-
04103, Leipzig, Germany
† The HTML version of this article has been enhanced with additional
colour.
‡ Electronic supplementary information (ESI) available: Crystal structure
determination and refinement details for 1–3. See DOI: 10.1039/b604804h
3772 | Dalton Trans., 2006, 3772–3776
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◦
˚
Table 1 Selected bond distances (A) and angles ( ) for complexes 1–3
[{Cu3(l3-OH)}{Cu3(l3-O)}(l4-btr)3(H2O)4(OH)2Cl6]Cl·0.5H2Oa (1)
Cu(1)–N(1)
Cu(1)–N(2a)
Cu(1)–O(1)
Cu(1)–O(2)
Cu(1)–Cl(1)
Cu(1)–O(1)–Cu(1a)
2.004(4) O(1)–Cu(1)–Cl(1)
1.996(4) N(1)–Cu(1)–Cl(1)
2.026(2) N(1)–Cu(1)–N(2a)
2.200(5) N(1)–Cu(1)–O(1)
2.294(1) N(1)–Cu(1)–O(2)
163.7(2)
89.7(1)
170.2(2)
88.2(1)
90.7(2)
97.7(3)
114.4(2)
O(1)–Cu(1)–O(2)
[{Cu3(l3-OH)}2(l3-btr)6(l4-btr)(l-Br)Br4]Br5·6H2O (2)
Cu(1)–O(1)
Cu(1)–N(1)
Cu(1)–N(3)
Cu(1)–N(6)
Cu(1)–N(13)
Cu(1)–Br(1)
Cu(2)–O(1)
Cu(2)–N(4)
Cu(2)–N(9)
2.040(3) Cu(2)–N(12)
2.000(5) Cu(2)–Br(2)
2.284(7)
2.779(1)
113.9(1)
91.1(2)
161.4(2)
90.2(1)
90.3(1)
179.5(2)
88.9(1)
2.012(5) Cu(1)–O(1)–Cu(2)
2.021(5) N(1)–Cu(1)–O(1)
2.440(9) N(1)–Cu(1)–N(3)
2.672(1) O(1)–Cu(1)–Br(1)
2.033(5) N(4)–Cu(2)–O(1)
2.012(4) N(9)–Cu(2)–O(1)
2.025(7) O(1)–Cu(2)–Br(2)
[{Cu3(l3-OH)}2(l3-btr)6(l4-btr)(l-Cl)Cl4]Cl5·8H2O (3)b
Cu(1)–Cl(1)
Cu(1)–O(1)
Cu(1)–N(1)
Cu(1)–N(7)
Cu(1)–N(16a)
Cu(1)–N(37)
Cu(2)–Cl(2)
Cu(2)–O(1)
Cu(2)–N(5b)
Cu(2)–N(8)
Cu(2)–N(13)
Cu(3)–Cl(3)
Cu(3)–O(1)
Cu(3)–N(2)
Cu(3)–N(10c)
Cu(3)–N(14)
Cu(3)–N(38)
Cu(4)–Cl(4)
Cu(4)–O(2)
Cu(4)–N(19)
2.601(3)
1.986(7)
2.047(10) Cu(4)–N(40)
2.014(10) Cu(5)–Cl(5)
1.990(9)
2.339(10) Cu(5)–N(20)
2.359(4)
1.973(9)
1.998(11) Cu(5)–N(41)
2.044(10) Cu(6)–Cl(1f)
2.135(9)
2.288(3)
2.296(10) Cu(6)–N(23g)
2.015(9) Cu(6)–N(31)
Cu(4)–N(25)
Cu(4)–N(35d)
2.037(10)
Fig. 1 Association of l3-hydroxo and l3-oxo clusters sustaining structure
1 by OH · · · O hydrogen bonding.
2.335(11)
2.055(10)
2.539(4)
Cu(5)–O(2)
1.963(8)
2.108(10)
2.012(10)
2.038(11)
2.416(10)
2.427(3)
Cu(5)–N(29e)
Cu(5)–N(32)
Cu(6)–O(2)
Cu(6)–N(26)
1.977(8)
2.056(10)
2.025(11)
2.039(10)
2.283(13) Cu(1)–O(1)–Cu(2)
1.997(10) Cu(1)–O(1)–Cu(3)
2.109(9)
2.279(3)
2.334(8)
121.1(4)
106.5(4)
114.1(4)
106.7(3)
111.6(3)
121.2(5)
Cu(2)–O(1)–Cu(3)
Cu(4)–O(2)–Cu(5)
Cu(4)–O(2)–Cu(6)
2.012(10) Cu(5)–O(2)–Cu(6)
a a: −0.5 + y, z, 0.5 + x. b a: x, −1 + y, z; b: 0.5 + x, 0.5 + y, z; c: −0.5 + x,
0.5 + y, z; d: −0.5 + x, −0.5 + y, z; e: x, 1 + y, z; f: x, −1 − y, −0.5 + z; g:
0.5 + x, −0.5 + y, z.
between the l3-hydroxo- and l3-oxo-moieties (i.e. Cu3OH–OCu3)
and facilitates very dense packing. When this bond is considered
for overall connectivity, the interpenetration disappears and a
peculiar and unique uninodal uniform self-catenated net is found
with topology Schla¨fli symbol {86}.
Fig. 2 Fragment of structure 1 showing four (out of eight) interpenetrat-
ing (10,3)-a nets. The triangles represent the tricopper clusters linked by
bitriazole connectors.
Though the framework solely occupies only 11.6% of the space,13
the entire structure was generated by interpenetration of eight
identical frameworks (four pairs of opposite chirality); this is
the highest degree of interpenetration of (10,3)-a nets observed
in a crystal structure14 and the second known example of class
IIIb interpenetration15 where four pairs of enantiochiral nets are
present.
A salient feature of the structure, unprecedented for molecular
systems, consists of the association between the tricopper clusters.
The short separation between pairs of l3-oxygen atoms, which are
The copper ions adopt a distorted square pyramidal coor-
dination, with equatorial l3-oxygen, two nitrogen atoms and
chloride ligand, and distal apical water (hydroxo) ligands (Table 1).
The trinuclear clusters adopt the packing pattern, which is very
characteristic of large nearly planar moieties possessing trigonal
symmetry, for example some of the 18-crown-6 complexes.16 In this
way four clusters are situated on the faces of a tetrahedron with
˚
edges of ca. 18 A and twelve apical oxygen atoms reside inside the
cage and appear to be arranged in a distorted icosahedron (Fig. 3).
˚
shifted by 0.49 A from the Cu3 planes towards each other (O · · · O
The shorter edges of this unprecedented ensemble (O · · · O 2.74,
˚
˚
3.02 and 3.65 A) are reasonable for hydrogen bonding.
2.712 A), indicates that directional hydrogen bonding occurs
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Fig. 3 Fragment of the structure 1, which shows mode of packing of four
symmetry related tricopper clusters.
The rich coordination functionality of the tricopper synthon,
which involves three chlorides in the equatorial plane and distal
apical aqua (hydroxo) ligands, provides wider possibilities for
framework design as was demonstrated by the structure of
[{Cu3(l3-OH)}2(l3-btr)6(l4-btr)(l-Br)Br4]Br5·6H2O (2). Thus the
chloride ligands in 1, which are trans with respect to the l3-oxygen
˚
atoms, are only weakly bound (2.294(1) A) due to a possible
interference with the adjacent triazolyl groups and therefore
this position is hardly suited for a larger bromide ion. Under
elimination of the terminal ligands from these positions, as may be
anticipated for the copper(II) bromide system, the molecular units
[Cu3(l3-OH)(btr)3]5+ become self-complementary since they com-
bine either acceptor or donor sites (unsaturated equatorial coor-
dination positions and the outer triazole-N donors) (Scheme 1,b).
Thus generation of the {[Cu3(l3-OH)(btr)3]}n planar (3,6)-network
by simple self-association (Fig. 4) involves the ligands as tridentate
Fig. 4 a) Six-connected 2D coordination subtopology in 2 and 3
originating in association of self-complementary units; b) the entire 3D
structure is sustained by cross-linking of the 2D subtopologies.
2
donors, with only one g -triazole function engaged within the
tricopper cluster. It is worth noting that such a structure may
be reproduced also with copper chloride, [{Cu3(l3-OH)}2(l3-
btr)6(l4-btr)(l-Cl)Cl4]Cl5·8H2O (3): it was essential to perform
crystallization relatively quickly, unlike for the preparation of
complex 1 (see Experimental section) and from this view the array
possibly illustrates an initial nucleation step in the system.
The 2D subtopologies in 2 and 3 are related to the non-covalent
(3,6)-networks (CH · · · N) of 1,3,5-tricyanobenzene and similar
3 + 3 self-complementary molecules of trigonal symmetry,17
but are quite remarkable for coordination polymers.18 Each
tricopper unit coordinates three distal axial chloride (bromide)
ions, one of them bridging between two clusters and this results
in association of the metal–organic subtopologies into double
for accommodation of guest molecules by multiple interactions.
The additional btr molecules, as pillar modules, extend the
chloride (bromide) bridged double layers into the 3D framework.
Considering these additional btr and chloride (bromide) bridges,
the overall 3D topology may be regarded as an eight-connected
primitive hexagonal net (Schla¨fli symbol {36;418;53;6}).
Conclusion
Our study demonstrates an efficient protocol for the integration of
polynuclear ensembles into extended arrays and the pathway, in
which the Cu3(l3-OH) core is applicable as a secondary building
block, for the generation of coordination frameworks. The results,
which are reported here, provide an attractive prototype for the
development of frameworks with multiple guest-binding sites
using general principles of crystal design and we are currently
exploring incorporation of the Cu3(l3-OH) clusters into porous
metal–organic structures.
˚
layers at 4.78 A. That the tricopper clusters retain an elec-
trophilic character at the opposite axial side was best reflected
by immobilization of an additional bitriazole molecule that fits
comfortably inside the cone-shaped binding pocket (geometrically
similar to that of boron subphthalocyanines)19 and interacts with
two copper atoms simultaneously (Fig. 5), which is prototypal
3774 | Dalton Trans., 2006, 3772–3776
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9–10 d, large green octahedra of complex 1 in 60% yield, as
a mixture with a minor product, Cu3Cl6(btr)4 (blue plates, ca.
10%). When CuBr2 (22.3 mg, 0.10 mmol) was used instead of
the chloride, the reaction led to complex 2 (40%). Well-developed
crystals of 2 were grown using a solution of CuBr2 in ethanol. Anal.
for 1, C12H24Cl7Cu6N18O8.5. Calc. (%): C, 12.15; H, 2.04; N, 21.27.
Found (%): C, 12.04; H, 1.92; N, 21.06. For 2, C28H42Br10Cu6N42O8.
Calc. (%): C, 14.78; H, 1.86; N, 25.86. Found (%): C, 14.49; H,
1.91; N, 25.74.
The same complex 1 crystallizes from an aqueous solution of
the components under slow evaporation at rt for several weeks.
However, when the crystallization occurs relatively quickly, it was
possible to isolate complex 3 in high yield.
Synthesis of 3. Diethyl ether–THF (1 : 1) vapor diffusion into
a solution of CuCl2·2H2O (17.0 mg, 0.10 mmol) and btr (13.6 mg,
0.10 mmol) in 1 mL water for 10–12 h affords green crystals of
the complex in 90% yield. Anal. for 3, C28H46Cl10Cu6N42O10. Calc.
(%): C, 18.01; H, 2.48; N, 31.52. Found (%): C, 17.86; H, 2.34; N,
31.12.
Fig. 5 Illustration of how the pair of tricopper clusters in 3 provides
accomodation of an additional btr molecule by multiple coordination
bonding. Note the presence of six- and five-coordinated copper ions [Cu(2)
and Cu(6)].
X-Ray crystallography
Crystallographic measurements were made at 213 K using a
Stoe Imaging Plate Diffraction System with Mo-Ka radiation
Experimental
˚
(k = 0.71073 A). The structures were solved by direct methods
4,4ꢀ-Bi(1,2,4-triazole) was prepared in 58% yield by reacting 4-
amino-4H-1,2,4-triazole and dimethylformamide azine using the
literature method.20 Examination of the reaction of bitriazole lig-
and towards copper(II) chloride (bromide) in aqueous or aqueous
alcohol media reveals that formation of l3-hydroxotricopper(II)
clusters dominates the structure of the products and is a suitably
predictable feature of the system.
using the program SHELXS-97.21 The refinement and all further
calculations were carried out using SHELXL-97.21 The non-H
atoms were refined anisotropically, using weighted full-matrix
least-squares of F2 (Table 2). CH and l3-OH hydrogen atoms
were added geometrically. Since structure 1 comprises symmetry
related hydroxo- and oxotricopper clusters, the OH hydrogen atom
is disordered over two structurally equal l3-O fragments, and it was
added with partial occupancy factor 0.5. Three non-coordinated
chloride ions in the structure of 3 were unequally disordered
over closely situated positions and only the major contributions
were refined anisotropically. In structure 2, the l4-btr ligand is
disordered between two symmetry related overlapping positions,
Syntheses
Synthesis of 1 and 2. Slow interdiffusion of solutions of
CuCl2·2H2O (34.0 mg, 0.20 mmol) in 3 mL methanol and btr
(27.2 mg, 0.20 mmol) in 1 mL water affords, over a period of
Table 2 Crystal data for [{Cu3(l3-OH)}{Cu3(l3-O)}(l4-btr)3(H2O)4(OH)2Cl6]Cl·0.5H2O (1), [{Cu3(l3-OH)}2(l3-btr)6(l4-btr)(l-Br)Br4]Br5·6H2O (2)
and [{Cu3(l3-OH)}2(l3-btr)6(l4-btr)(l-Cl)Cl4]Cl5·8H2O (3)
1
2
3
Formula
M
C12H24Cl7Cu6N18O8.50
1185.88
C28H42Br10Cu6N42O8
2275.38
Monoclinic
C28H46Cl10Cu6N42O10
1866.81
Monoclinic
Crystal system
Space group, Z
Cubic
¯
Fd3c, 32
C2/m, 2
Cc, 4
˚
a/A
30.0968(12)
11.9996(11)
21.067(2)
15.648(2)
109.55(1)
3727.4(6)
71.10
21.359(2)
12.0195(8)
28.954(2)
97.90(1)
7362.8(10)
21.38
˚
b/A
˚
c/A
b/◦
3
˚
U/A
27262(2)
42.97
2.311
l(Mo-Ka)/cm−1
Dc/g cm−3
2.027
53.5
1.684
53.5
◦
2hmax
/
51.8
Measured/unique reflns
Parameters refined
R1, wR2 (I > 2r(I))
R1, wR2 (all data)
8263/1078
81
0.048, 0.144
0.054, 0.147
1.37, −0.89
11860/3893
237
0.049, 0.106
0.082, 0.112
1.00, −1.28
17532/12531
846
0.076, 0.198a
0.084, 0.202
1.42, −0.84
−3
˚
Max, min peak/e A
a Flack parameter x = 0.04(2).
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The Royal Society of Chemistry 2006
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as donor of four Cu–N bonds towards a pair of tricopper clusters
and this disorded was refined without constraints in geometry
(alternative refinements of the structure either in space groups
C2 or Cm did not lead to a ordered model). Some of the non-
coordinated bromide ions and water molecules in this structure are
badly disordered and the remaining electron density was modeled
using Squeeze.13 Graphical visualisation of the structures was
made using the program Diamond.22
9 S. Ferrer, J. G. Haasnoot, J. Reedijk, E. Mu¨ller, M. Biagini-Cingi, M.
Lanfranchi, A. M. Manotti-Lanfredi and J. Ribas, Inorg. Chem., 2000,
39, 1859; J.-C. Liu, G.-C. Guo, J.-S. Huang and X.-Z. You, Inorg. Chem.,
2003, 42, 235; S. Ferrer, F. Lloret, I. Bertomeu, G. Alzuet, J. Borras, S.
Garcıa-Granda, M. Liu-Gonzalez and J. G. Haasnoot, Inorg. Chem.,
2002, 41, 5821.
10 X. Liu, M. P. de Miranda, E. J. L. McInnes, C. A. Kilner and M. A.
Halcrow, Dalton Trans., 2004, 59; M. Casarin, C. Corvaja, C. Di Nicola,
D. Falcomer, L. Franco, M. Monari, L. Pandolfo, C. Pettinari and F.
Piccinelli, Inorg. Chem., 2005, 44, 6265; R. Boca, L. Dlhan, G. Mezei,
T. Ortiz-Perez, R. G. Raptis and J. Telser, Inorg. Chem., 2003, 42, 5801;
P. A. Angaridis, P. Baran, R. Boca, F. Cervantes-Lee, W. Haase, G.
Mezei, R. G. Raptis and R. Werner, Inorg. Chem., 2002, 41, 2219.
11 Bitriazole was known entirely as an N,Nꢀ-bidentate bridging ligand;
the twist angle along the N–N single bond is in the range 50 to 90◦:
Y. Garcia, O. Kahn, L. Rabardel, B. Chansou, L. Salmon and J. P.
Tuchagues, Inorg. Chem., 1999, 38, 4663; C. L. Zilverentant, W. L.
Driessen, J. G. Haasnoot, J. J. A. Kolnaar and J. Reedijk, Inorg.
Chim. Acta, 1998, 282, 257; A. Ozarowski, Yu Shunzhong, B. R.
McGarvey, A. Mislanker and J. E. Drake, Inorg. Chem., 1991, 30, 3167;
W. Vreugdenhil, J. H. van Diemen, R. A. G. de Graaff, J. G. Haasnoot,
J. Reedijk, A. M. van der Kraan, O. Kahn and J. Zarembowitch,
Polyhedron, 1990, 9, 2971; M. Biagini-Cingi, A. M. Manotti-Lanfredi,
F. Ugozzoli, J. G. Haasnoot and J. Reedijk, Gazz. Chim. Ital., 1994,
124, 509.
CCDC reference numbers 600030–600032.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b604804h
Acknowledgements
The work was in part supported by a grant from Deutsche
Forschungsgemeinschaft UKR 17/1/06 (HK and KVD).
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