Formation of hexagonal coordination complexes

Article abstract of DOI:10.1002/ejic.200400722

The synthesis of the ligand 1,3-bis(3′-pyridylethynyl)benzene and the coordination complex formed with copper(II) acetate is described. The complex is hexagonal with two ligands bridged by paddlewheel-shaped dimeric copper(II) acetate moieties. The complexes are packed in such a way that the benzene rings from two separate complexes penetrate into the central cavity. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.

Full text of DOI:10.1002/ejic.200400722

SHORT COMMUNICATION
Formation of Hexagonal Coordination Complexes
Nate Schultheiss,[a] Joseph M. Ellsworth,[a] Eric Bosch,*[a] and Charles L. Barnes[b]
Keywords: Crystal engineering / N ligands / Metallacycles / Microporous materials
The synthesis of the ligand 1,3-bis(3Ј-pyridylethynyl)ben- that the benzene rings from two separate complexes penet-
zene and the coordination complex formed with copper(II
acetate is described. The complex is hexagonal with two li-
gands bridged by paddlewheel-shaped dimeric copper(II
)
rate into the central cavity.
)
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
acetate moieties. The complexes are packed in such a way
Germany, 2005)
Introduction
emental analysis of the bulk solid indicated that a 1:2 li-
gand/CuII complex was formed. Single-crystal X-ray analy-
sis revealed this to be a hexagonal 2:4 coordination complex
as shown in Figure 1.[10]
The synthesis of porous solids is a research area of cur-
rent interest.[1Ϫ4] For example solids that contain channel-
like void spaces are attractive goals with potential appli-
cations in molecular adsorption, ion exchange, and also
heterogeneous catalysis. Hexagonal channels and cavities
are often found in nature, and several approaches to the
synthesis of hexagonal channels have been reported. Moore,
for example, reported the formation of a purely organic po-
rous solid with wide channels based on the π-stacking and
hydrogen bonding of a planar hexagonal macrocycle com-
prising six phenols linked by meta-ethynyl groups.[5] Robson
reported a coordination chemistry approach and charac-
terized a large hexagonal complex on self-assembly of 2,4,6-
tris(4Ј-pyridyl)-1,3,5-triazine with copper(ii) acetate.[6] That
coordination network did not contain channels because of
the offset packing of adjacent sheets of the coordination
network. In this report we describe a different coordination
chemistry approach to the preparation of hexagonal
channels.
Results and Discussion
Figure 1. Ortep view of the 2:4 complex formed between 1 and
copper(ii) acetate; ellipsoids drawn at the 50% probability level
As ligand we chose to prepare the bidentate ligand 1,3-
bis(3Ј-pyridylethynyl)benzene, 1, and to self-assemble this
with metals that favor linear coordination as shown in
Equation (1). Sonagashira coupling[7] of 3-bromopyridine
with 1,3-diethynylbenzene yielded the ligand 1 in good yield
as shown in Equation (2).[8] We then allowed the ligand 1
to self assemble with copper(ii) acetate in acetonitrile solu-
tion and obtained green diamond-shaped crystals.[9] El-
(1)
[a]
Department of Chemistry, Southwest Missouri State
University,
Springfield, MO 65804, USA
[b]
Department of Chemistry, University of Missouri,
Columbia, MO 65211, USA
Eur. J. Inorg. Chem. 2005, 45Ϫ46
DOI: 10.1002/ejic.200400722
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
45

N. Schultheiss, J. M. Ellsworth, E. Bosch, C. L. Barnes
SHORT COMMUNICATION
two complexes partially penetrating the central cavity of a
third complex. This is shown in Figure 2.
(2)
Acknowledgments
We thank the Petroleum Research Fund administered by the ACS
(Grant # 37506-B3) and the Graduate College at SMSU for partial
funding of this research.
The complex between two ligands and two copper(ii)
acetate dimeric units forms a slightly irregular hexagon as
shown in Figure 1. The copper(ii) acetate linkage gives
[1]
M. J. Zaworotko, Angew. Chem. Int. Ed. 2000, 39, 3052Ϫ3054.
[2]
P. H Dinolfo, J. T. Hupp, Chem. Mater. 2001, 13, 3113Ϫ3125.
˚
[3]
longer sides with a N(1)ϪN(2) distance of 6.957 A, while
O. M. Yaghi, H. Li, C. Davis, D. Richardson, T. L. Groy, Acc.
the C(2)ϪC(8) and C(10)ϪC(17) distances are 4.067 and
4.065 A, respectively. The copper acetate paddlewheel forms
Chem. Res. 1998, 31, 474Ϫ484.
[4]
˚
M. Eddaoudi, D. B. Moler, H. Li, B. Chen, T. M. Reineke, M.
OЈKeeffe, O. M. Yaghi, Acc. Chem. Res. 2001, 34, 319Ϫ330.
an almost linear connection between the pair of ligand mol-
ecules with nitrogenϪcopperϪcopper angles of 174.82(6)
and 177.43(7)°. The copperϪnitrogen bond lengths of
[5]
D. Venkataraman, S. Lee, J. Zhang, J. S. Moore, Nature 1994,
371, 591Ϫ593.
[6]
S. R. Batten, B. F. Hoskins, B. Moubaraki, K. S. Murray, R.
Robson, Chem. Commun. 2000, 1095Ϫ1096.
K. Sonogashira, Metal-Catalyzed Cross-Coupling Reactions
(Eds.: F. Diederich, P. J. Stang), Wiley-VCH, New York, 1998,
pp. 203Ϫ229.
1,3-Diethynylbenzene (1.26 g, 10 mmol) was added with the aid
˚
2.185(2) and 2.175(2) A and the copperϪcopper bond
[7]
˚
length of 2.6053(5) A are normal. The copperϪoxygen
˚
˚
bond lengths range from 1.959(2) A to 1.987(2) A, and the
oxygenϪcopperϪoxygen bond angles on each side of the
paddlewheel range from 87.56(9) to 92.32(9)°. The alkynes
are undistorted with normal triple bond lengths of 1.190(4)
[8]
of
a syringe to a mixture of 3-bromopyridine (3.26 g,
20.6 mmol), bis(triphenylphosphane)palladium(ii) dichloride
(150 mg), CuI (15 mng), and triphenylphosphane (150 mg) in
diethylamine (25 mL). Nitrogen was bubbled though the mix-
ture for 10 minutes, and the reaction was heated to 60 °C under
nitrogen for 16 h. The crude product was purified, by precipi-
tation from ethyl acetate with hexanes, as a white powder in
64% yield (1.02 g). 1H NMR (CDCl3): δ ϭ 7.38Ϫ7.26 (m, 3 H,
ArH), 7.56Ϫ7.52 (m, 2 H, ArH), 7.75 (t, J ϭ 1.5 Hz, 1 H,
ArH), 7.81 (td, J ϭ 1.8, 8.0 Hz, 2 H, ArH), 8.57 (dd, J ϭ 1.8,
5.2 Hz, 2 H, ArH), 8.78 (dd, J ϭ 0.8, 2.0 Hz, 2 H, ArH) ppm.
13C NMR: δ ϭ 86.7, 91.5, 120.1, 123.0, 128.6, 131.8, 134.7,
138.4, 148.7, 152.3 ppm. C20H12N2 (280.32): calcd. C 85.71, H
4.29, N 10.00; found C 85.55, H 4.32, N 9.90.
˚
and 1.191(4) A and angles about the sp C atoms between
177.3(4) and 179.3(4)°. The pyridyl rings are slightly twisted
with respect to the central benzene ring with torsional
angles of approximately 28 and 13°.
Unfortunately, the hexagonal complexes do not stack on
top of each other to form porous materials Ϫ instead indi-
vidual complexes stack in an offset manner with the end of
[9]
A mixture of acetonitrile (2 mL) and dichloromethane (2 mL)
was layered over a solution of 1,3-bis(3Ј-pyridylethynyl)ben-
zene (11.0 mg, 0.04 mmol) in dichloromethane (2 mL). A solu-
tion of copper(ii) acetate monohydrate (16.0 mg, 0.08 mmol) in
acetonitrile (2 mL) was carefully layered over that. The vial was
capped and placed in the dark. Green diamond-shaped
crystals formed after 2 days (14.7 mg, 59%). m.p. 222 °C.
C28H24N2Cu2O8 (643.6): calcd. C 52.25, H 3.76, N 4.35; found
C 52.32, H 3.68, N 4.37.
[10]
Crystal size 0.40 ϫ 0.25 ϫ 0.05 mm, C28H24Cu2N2O8, mol.
˚
mass 643.57; monoclinic, C2/c, a ϭ 36.5577(17) A, b ϭ
˚
˚
7.8999(4) A, c ϭ 21.4256(11) A; β ϭ 100.3440(10)°; V ϭ
3
3
˚
6087.2(5) A ; Z ϭ 8; ρ (calculated) ϭ 1.404 Mg/m ; reflections
collected ϭ 21246 (6700 unique); F(000) ϭ 2624; Absorption
coefficient ϭ 1.445 mmϪ1; 1.93 Ͻ θ Ͻ 27.14 ; max. and min.
transmission ϭ 0.93 and 0.59; final R indices [I Ͼ 2σ(I)], R1 ϭ
0.0440, wR2 ϭ 0.1005; largest diff. peak and hole ϭ 0.660 and
Ϫ0.382 e·AϪ3. CCDC-246104 contains the supplementary
˚
crystallographic data for this paper. These data can be obtained
free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or
from the Cambridge Crystallographic Data Centre, 12 Union
Road, Cambridge CB2 1EZ, UK; Fax: ϩ44-1223-336-033;
E-mail: deposit@ccdc.cam.ac.uk].
Figure 2. A: The packing in the unit cell viewed along the a axis;
B: view showing the partial penetration of two complexes into a
central tilted complex.
Received August 25, 2004
46
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2005, 45Ϫ46