Dinuclear Zn(II) Polymer Consisting of Channels Formed by π,π-Stacking Interactions with a Flow of Nitrate Anions through the Channels Laura Valencia,*,† Paulo Pérez-Lourido,† Rufina Bastida,*,‡ and Alejandro Macías‡
CRYSTAL GROWTH & DESIGN 2008 VOL. 8, NO. 7 2080–2082
UniVersidad de Vigo, Departamento de Quı´mica Inorga´nica, Facultad de Quı´mica, As Lagoas-Marcosende, 36310 Vigo, PonteVedra, Spain, and UniVersidad de Santiago de Compostela, Departamento de Quı´mica Inorga´nica, Facultad de Quı´mica, AV. de las Ciencias s/n, 15782 Santiago de Compostela, Spain ReceiVed March 21, 2008; ReVised Manuscript ReceiVed April 16, 2008
ABSTRACT: An interesting metallo-organic polymeric architecture of a Zn(II) dinuclear pendant-armed macrocyclic complex was obtained. The structure consists of a supramolecular architecture of infinite pillars comprised of [Zn2L(NO3)2]2+ units and free nitrate ions. This structure has tubular channels along the c-axis, and these are stabilized by the presence of multiple inter- and intramolecular π,π-stacking interactions. A flow of uncoordinated nitrate anions is present within the channels. The supramolecular construction of specific architectures from well-defined molecular building blocks has been an active area of chemical research over the past few years.1,2 Recently, nanostructures have come to represent a well-established group of coordination compounds.3 The diversity of coordination nanostructures formed by the assembly of transition metal junctions and bridging ligands makes them suitable candidates for use as construction blocks for larger supramolecular arrays.4 It is well-known that if discrete metallo-supramolecular species contain additional peripheral binding sites they can assemble to give polymeric structures.5 Similarly, aggregation to give polymers can be supported by additional bridging ligands6 or coordinated counterions.7 A knowledge of the principles of nanostructure formation through polymerization is important not only from the viewpoint of coordination chemistry, but also for the future development of increasingly intricate and functional coordination networks. In this sense, noncovalent interactions such as hydrogen bonds and π,π-stacking are the main driving forces behind this self-assembly process.8 On the other hand, in recent decades one of the main targets in the field of metallo-supramolecular chemistry is anion recognition9 by artificial receptors for chemical transport and screening by membrane channels in biological systems.1b,3b,10 In particular, ionic channels are important in the cell membranes of nerves, muscles, and synapses.11 Ion transport through these cell membranes is precisely controlled by the opening and closing of ionic channels. Although many porous metal-organic frameworks with unique structures have been obtained, those with specifically shaped channels are rare.12,13 Polyamine macrocycles containing cavities of an appropriate shape and dimensions may be able to hold several metal centers.14,15 The distance between the metal ions can be varied by appropriate synthetic modulation of the dimensions of the macrocyclic cavity and of the ligand flexibility. At the same time, the chemical properties of the metal centers depend on the ligational properties of the chelating sites, and, therefore, appropriate design of the metal binding unit may lead to polynuclear metal complexes with different reactivities and catalytic properties. For these reasons, several dinuclear Zn(II) complexes with polyazamacrocycles have been used to mimic the multinuclear metal arrays at the active sites of hydrolytic metallo-enzymes.16 Pendant-armed macrocyclic ligands and their metal complexes have recently attracted a great deal of interest owing to the fact that the incorporation of functionalized pendant-arms provides additional * To whom correspondence should be addressed. E-mail:
[email protected] (L.V.);
[email protected] (R.B.). † Universidad de Vigo. ‡ University of Santiago de Compostela.
Scheme 1. Pendant-Armed Hexaaza Macrocyclic Ligand (L)
coordinating functions in the macrocycle, enhances complex stability, or promotes the formation of supramolecular structures with different properties and applications.17 As a consequence of our work on metal complexes with macrocylic ligands,18 we chose L (Scheme 1) as a bridging pendantarmed macrocyclic ligand to construct new framework materials with novel structures and special properties based on the combination of the bridging coordination ability and steric bulk of L. The ligand is potentially decadentate containing two bridgehead pyridyl rings in the macrocyclic framework and four pyridyl pendant-arm groups attached to four tertiary amine nitrogen atoms. We report here an interesting polymeric Zn(II) dinuclear pendantarmed macrocyclic complex supported by π,π-stacking interactions. The controlled aggregation produces open frameworks with tubular channels through which there is a flow of free nitrate anions. The dinuclear Zn(II) complex was obtained in a direct synthesis between the hydrated Zn(II) nitrate salt and the ligand in a 2:1 molar ratio in acetonitrile. After 4 h under reflux the solution was allowed to cool and the complex crystallized as colorless prisms.19 The single-crystal X-ray structure of the complex [Zn2L(NO3)2](NO3)2 · H2O was determined at low temperature.20 The complex crystallizes in the I4(1)/a group of the orthorhombic system, and the asymmetric unit is comprised of the dinuclear cation [Zn2L(NO3)2]2+, two independent nitrate groups (one of which is disordered in two positions) and a crystallization water molecule. In the [Zn2L(NO3)2]2+ cation (Figure 1), two crystallographically different zinc atoms are located within the macrocyclic cavity in a similar pentacoordinated environment. Each of the Zn(II) ions is coordinated by the N atom of one pyridyl bridgehead group, one amine nitrogen atom contiguous to that pyridyl ring and its corresponding pyridyl pendant-arm, and
10.1021/cg800302w CCC: $40.75 2008 American Chemical Society Published on Web 05/21/2008
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Figure 1. A representation of the molecular structure of [Zn2L(NO3)2]2+.
to another pyridyl pendant group of the other amine nitrogen contiguous to the coordinated pyridyl bridgehead. The fifth coordination position is completed by one oxygen atom of a monodentate nitrate anion. The two remaining amine nitrogen atoms are not coordinated to the metal ions. Thus, the zinc atoms are five coordinate with an N4O donor set. The τ factor21 is 0.31 for Zn(1) [O(1N)Zn(1)N(6), 150.1(2)°; N(1)Zn(1) N(10), 131.5(3)°] and 0.27 for Zn(2) [O(4N)Zn(2)N(5), 151.5(2)°; N(4)Zn(2)N(8), 135.5(3)°], showing that the coordination geometry around both metal ions can be better described as a severely distorted square pyramid rather than a trigonal bipyramid. The intramolecular metal-metal distance is 6.013 Å. N(7) and N(8) from the pyridyl pendant rings occupy the apical position of the pyramid for Zn(1) and Zn(2), respectively, while the rms from the mean basal plane [O(1N) N(1) N(6) N(10)] is 0.12 for Zn(1) and 0.17 for Zn(2) [O(4n) N(5) N(4) N(9)]. The Zn(1) and Zn(2) atoms are displaced by 0.68 and 0.70 Å from that basal plane toward the apical site, respectively. The main distortion from a regular geometry can be attributed to the values of the angles at the metal atoms for the two fivemembered and for the eight-membered chelate rings, which deviate significantly from 90°; 77.3(3), 75.5(2), and 131.5(3)° for N(1)Zn(1)N(6), N(6)Zn(1)N(10), and N(1)Zn(1)N(7), respectively, and 76.5(3), 75.3(3), and 135.5(3)° for N(4)Zn(2)N(5), N(5)Zn(1)N(9), and N(4)Zn(1)N(8), respectively. The ZnNpy distances vary from 2.071(7) to 2.123(7) Å [Zn(2)N(4) and Zn(1)N(1), respectively], with an average value of 2.102 Å. The longest coordination bond corresponds to the amine nitrogen atoms [Zn(1)N(6) 2.306(7), Zn(2)N(5) 2.301(7) Å], and these are longer than those in other similar N4O pentacoordinated Zn(II) complexes.22 For the ZnO bond length, the average value is 2.104 Å, which is similar to that found in other monodentate nitrate complexes of pentacoordinated Zn(II).23 The macrocyclic ligand has a step conformation in which the dihedral angle between the pyridine rings of the macrocyclic backbone [N(1)C(1)C(5), rms ) 0.0063 and N(4)C(10)C(14), rms ) 0.0160] is 5.57(0.45)° and the planes containing each of these rings are ca. 5.6 Å away from one another but are almost perpendicular (78.5 and 82.5°, respectively) to the plane described by the four amine nitrogen atoms. A view of the crystal packing shows that the dinuclear complex displays interesting structural features. Analysis of the supramolecular assembly reveals that all aromatic units are packed in such way that an open framework of infinite pillars comprising of [Zn2L(NO3)2]2+ units and free nitrate ions are formed, giving rise to tubular channels through the c axis (Figure 2). The assembly of this supramolecular architecture can be considered as the result of several intermolecular face-to-face π,πstacking interactions: (i) between pyridyl pendant-arm groups, (ii) between these pyridyl pendant groups and uncoordinated nitrate
Figure 2. Packing of the polymeric complex in a grid surrounded by nitrate anions and uncoordinated water molecules in the lattice.
Figure 3. Partial view of the polymer showing the different π,π-stacking interactions between pyridyl groups and nitrate ions.
anions, (iii) between pyridyl bridgehead groups of different macrocyclic frameworks. In addition, intramolecular π,π-interactions between pyridyl pendant-arm groups and pyridyl bridgehead groups are observed. If we consider only the π,π-stacking interactions in the direction of the tubular columns, the leitmotif repetition could be determined by the sequence: -py(pendt)-(3.9 Å)NO3--(4.1 Å)-py(pendt)-(3.9 Å)-py(pendt)- (Figure 3). This nitrate anion establishes asymmetric intermolecular π,π-stacking interactions with the pendant pyridyl group of two different [Zn2L(NO3)2]2+ units. If we consider the distance between the centroid of the pyridyl pendant-arm groups and the N atom of the nitrate group as analogous to the centroid-centroid distance, the (dcc) between the nitrate ion and the pyridyl ring is 3.9 Å but the distance between the planes containing these residues is 2.63 Å, a situation that means a slipped angle of 47.6°. The dcc of this nitrate anion and the other pyridyl ring is 4.1 Å, while the distance between the planes is 3.44 Å, which corresponds to a slipped angle of 32.9°. The nitrate ion is slightly tilted with respect to the pyridyl groups, with dihedral angles of 10.92° and 8.82°, respectively. The face-to-face π,π-stacking interactions between these pyridyl pendant-arm groups give rise to a distance between centroids (dcc) of 3.9 Å and a distance between planes (dplanes) of 3.5 Å. The other intermolecular face-to-face π,π-interactions observed between the pyridyl bridgehead groups of different macrocycles have a dcc of 3.9 Å and dplanes of 3.3 Å. Furthermore, intramolecular π,πinteractions are observed between the pyridyl bridgehead N(1)-
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(9) (10) (11) (12) (13) (14) (15)
Figure 4. Different views of the supramolecular structure with the nitrate anions filling the channel.
C(1)C(5) and the pyridyl pendant group N(8)C(26)C(30) (dcc ) 4.3 Å and these planes are tilted with an angle of 30.5°) and between N(4)C(10)-C(14) and the pendant N(7)C(20)C(24) (dcc ) 4.0 Å and a tilt angle of 26.92°). However, the latter two π,π-stacking interactions are not oriented in the direction of the tubular columns. Although a CSD search reveals that this sort of π,π-interaction between pyridine rings and nitrate ions is present in previously reported structures,24 to the best of our knowledge this is the first time that this sort of interaction has produced a supramolecular architecture of infinite tubular channels.25 Nitrate ions play three different roles in the crystal. Some nitrate ions are directly bonded to the Zn(II) ions, as shown previously. There are also nitrate ions that are π-stacked with the pyridine rings to give the tubular channels, while the remaining free nitrate anions cross the channels and occupy disordered positions within it. These disordered nitrate ions are present in the asymmetric unit and occupy the central part of the channels, thus representing a flow of nitrate ions through the channel (Figure 4). In conclusion, we present a new and interesting structurally characterized example of a polymeric dinuclear Zn(II) pendantarmed aza-macroclyclic complex. The structure shows [Zn2L(NO3)2]2+ units stabilized by the presence of multiple inter- and intramolecular π,π-stacking interactions. The large central hole in the polymer is occupied by uncoordinated nitrate anions.
(16) (17) (18)
(19)
(20)
Acknowledgment. We thank Xunta de Galicia (PGIDT01PXI20901PR) for financial support. Intensity measurements were performed at the Unidade de Raios X, University of Vigo, SPAIN. Also, we can thank L. Botana for the TG analysis.
References (1) (a) Lehn, J.-M. In Behr, J.-P., Ed. PerspectiVes in Supramolecular Chemistry, Vol. 1; Wiley: Chichester, 1994. (b) Lehn, J.-M. In Hamilton, A. D., Ed. PerspectiVes in Supramolecular Chemistry; Wiley: Chichester, 1996; Vol. 3. (2) (a) Takahashi, S.; Kariya, M.; Yatake, T.; Sonogashira, K.; Hagihara, N. Macromolecules 1978, 11, 1063. (b) Atwood, J. L.; Davies, J. E.; MacNicol, D. Inclusion Compounds; Academic Press: Oxford, 1991. (3) (a) Olenyuk, B.; Fechtenko¨tter, A.; Stang, P. J. J. Chem. Soc., Dalton Trans. 1998, 1707. (b) Piguet, C.; Bernardinelli, G.; Hopfgartner, C. Chem. ReV. 1997, 97, 2005. (4) Fyfe, M. C. T.; Stoddart, J. F. Acc. Chem. Res. 1997, 30, 393. (5) Loi, M.; Hosseini, M. W.; Jouaiti, A.; De Cian, A.; Fischer, J. Eur. J. Inorg. Chem. 1999, 1981. (6) (a) Sharma, C. V. K.; Rogers, R. D. Cryst. Eng. 1999, 1, 19. (b) Withrsby, M. A.; Blake, A. J.; Champness, N. R.; Cooke, P. A.; Hubberstey, P.; Schro¨der, M. Cryst. Eng. 1999, 2, 123. (7) Albrecht, M.; Fro¨hlich, R. J. Am. Chem. Soc. 1997, 119, 1656. (8) (a) Custelcean, R.; Afloroaei, C.; Vlassa, M.; Polverejan, M. Angew.
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Chem. 2000, 112, 3224. (b) Moorthy, J. N.; Natarajan, R.; Venugopalan, P. Angew. Chem. 2002, 41, 3417. Bianchi, A.; Bowman-James, K.; Garcia-Espan˜a E., Eds. Supramolecular Chemistry of Anions; Wiley-VCH: New York, 1997. Albrecht, M. Chem. ReV. 2001, 101, 3457. Stryer, L. Biochemistry; W. H. Freeman: New York, 1995. (a) Davidson, G. J. E.; Loeb, S. J. Angew. Chem. 2003, 115, 78. (b) Cui, Y.; Lee, S. J.; Lin, W. J. Am. Chem. Soc. 2003, 125, 6014. (a) Bradshaw, J. S.; Krakowiak, K. E.; Izatt, R. M., Eds. Chemistry of Heterocyclic Compounds. In Aza-Crown Macrocycles, Wiley: New York, 1993; Vol. 51. (a) Okawa, H.; Furutachi, H.; Fenton, D. E. Coord. Chem. ReV. 1998, 174, 51. Schneider, H.-J.; Yatsimirsky, A. Metal Ions in Biological Systems; Siegel, H.; Siegel, A., Eds. Marcel Dekker: New York, 2003; Vol. 40. (a) Iranzo, O.; Elmer, T.; Richard, J. P.; Morrow, J. R. Inorg. Chem. 2003, 42, 7737. (b) Yang, M.-Y.; Richard, J. P.; Morrow, J. R. Chem. Commun. 2003, 2832. (a) Rybak-Akinova, E. V.; Nazarenko, A. Y.; Silchenco, S. S. Inorg. Chem. 1999, 38, 2974. (b) Botta, M. Eur. J. Inorg. Chem. 2000, 399. (a) Fernandez-Fernandez, Ma del C.; Bastida, R.; Macı´as, A.; Pe´rezLourido, P.; Valencia, L. Inorg. Chem. 2006, 45, 2266. (b) Valencia, L.; Bastida, R.; Macias, A.; Vicente, M.; Perez-Lourido, P. New J. Chem. 2005, 29, 424. [Zn2L(NO3)2](NO3)2 · H2O: Anal. Calc for C42H48N14O13Zn2 (MW: 1086): C, 46.5; H, 4.3, N, 18.1. Found: C, 46.2, H, 4.1, N, 18.3%. Yield: 76%. IR (KBr, cm-1): 1608, 1586, 1436 [ν(CdC) and ν(CdN)py], 1445, 1380, 1319, 824 [ν(NO3-)]. LSI-MS (m/z): 884(8%), [Zn2L(NO3)]3+; 819(12%), [ZnL(NO3)]+; 757(17%), [ZnL]2+. ΛM/ Ω-1 cm2 mol-1 (in CH3CN): 366 (3:1). The X-ray crystal measurements were collected on a Bruker SMART CCD 1000 area diffractometer at 173(2) K. All data were corrected for Lorentz and polarization effects. Empirical absorption corrections were also applied for all the crystal structures obtained.26 Complex scattering factors were taken from the program package SHELXTL.27 The structure was solved by direct methods, which revealed the positions of all non-hydrogen atoms. The structure was refined on F2 by a full-matrix least-squares procedure using anisotropic displacement parameters for all non-hydrogen atoms, except for O7N, O8N, O9N, O10N, O11N, O12N, N4N, N5N, O13N, O14N, O15N, and O1W, which were refined as isotropic. The hydrogen atoms were located in their calculated positions and refined using a riding model. Molecular graphics were generated using ORTEP-3.28 Crystal data: C42H46N14O13Zn2, Mr ) 1085.67, orthorhombic, space group I4(1)/a, a ) b ) 42.289(3) Å, c ) 10.9873 Å, V ) 19649(3) Å3, Z ) 16, µ ) 1.053 mm-1, Fχald ) 1.468 g cm-3, λ(MokR) ) 0.71073 Å, GOF ) 1.067, R1 (wR2) ) 0.1022 (0.3006), 10730 (Rint ) 0.0947) independent reflections out of a total of 45 934 reflections with 654 parameters. CCDC 673693 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge viawww.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB21EZ, UK; fax: (+44)1223-336-033; or
[email protected]). Addison, J. A. W.; Rao, T. N.; Reedijk, J.; van Rinj, J.; Verschoor, G. C. J. Chem. Soc., Dalton Trans. 1984, 1349. τ ) (β-R)/60, τ ) 1, trigonal bipyramid and τ ) 0, square pyramid. Mareque-Rivas, J. C.; Torres-Martin de Rosales, R.; Parsons, S. Chem. Commun. 2004, 610. Pallenberg, A. J.; Marschner, T. M.; Barnhart, D. M. Polyhedron 1997, 16, 2711. Mooibroek, T. J.; Black, C. A.; Gamez, P.; Reedijk, J. Cryst. Growth Des. 2008, 8, 1082–1093. Valencia, L.; Bastida, R.; Fernandez-Fernandez, M. del C.; Macias, A.; Vicente, M. Inorg. Chim. Acta 2005, 358, 2618. Sheldrick, G. M. Sadabs, Program for empirical absorption correction of area detector data, University of Go¨ttingen: Germany, 1996. SHELXTL version, an integrated system for solving and refining crystal structures from diffraction data (Revision 5.1), Bruker AXS LTD. Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
CG800302W
