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CrystEngComm, 2000, 17
Reproducible phenazine molecular stacks
Venkat R. Thalladi,a Tanja Smolka,b Roland Boese*a and Reiner Sustmann*b
a Institut für Anorganische Chemie, Universität-GH Essen, Universitätsstraße 5-7, D-45117 Essen, Germany. E-mail:[email protected] Institut für Organische Chemie, Universität-GH Essen, Universitätsstraße 5-7, D-45117 Essen, Germany. E-mail:[email protected]
Received 11th May 2000, Accepted 6th June 2000, Published 20th June 2000
Single crystal X-ray diffraction analyses of the 2 : 1 complexes of phenazine with hydroquinone and 1,5-dihydroxynaphthaleneand the 3 : 1 complex of phenazine with 4,4´-dihydroxybiphenyl have been performed. It is shown that in these complexes andalso in the 3 : 1 complex of phenazine with 5,10-dihydrophenazine, phenazine forms a host framework consisting of one-dimensional channels. The variation of guest molecules and attendant variations in the hydrogen bond patterns, and thereproducibility of phenazine molecular stacks are described.
IntroductionThere has been much recent interest in the use of phenazineas a template in crystal engineering. The electron richaromatic system in phenazine enables it to be a good π-donor and the disposition of the two aromatic N atoms in adefined geometry enables it to be a good hydrogen bondacceptor. Accordingly, phenazine has been employed in thedesign of charge-transfer complexes1,2 and hydrogenbonded assemblies.3,4 Our own work focussed on the use ofphenazine based hydrogen bonded co-crystals inphotochromic applications and the development of crystalengineering strategies.5–8 In this work we report the crystalstructures of two 2 : 1 complexes of phenazine withhydroquinone (HQ) and 1,5-dihydroxynaphthalene (DHN)and one 3 : 1 complex of phenazine with 4,4´-dihydroxybiphenyl (DHBP). We compare these structureswith that of the 3 : 1 complex of phenazine and 1,5-dihydrophenazine (DHP) and illustrate that phenazinemolecular stacks are a common feature in these structures.
Results and discussionThe present work was initiated when, as part of exploringthe molecular complexes of phenazine with varioushydrogen bond donors, it had been found that phenazineforms a 2 : 1 molecular complex (1) with HQ, rather than a1 : 1 complex as would be expected from O–H···Nhydrogen bond requirements (two N atoms in phenazineand two OH groups in HQ). Single crystals of complex 1(mp 234–236 °C) were obtained when an ethyl acetatesolution containing equimolar mixture of phenazine and
HQ was slowly evaporated. X-ray diffraction analysis ofcomplex 1 (Table 1) showed that it belongs to the spacegroup 1P with the HQ molecules positioned on inversioncentres and phenazine molecules located on generalpositions. While both the OH groups of HQ act as O–H···Nhydrogen bond donors, only one of the two N atoms inphenazine acts as an O–H···N acceptor. Thus each HQmolecule is linked to two phenazine molecules through O–H···N hydrogen bonds (Table 2) leading to a discrete O–H···N assembly. The non-participation of one of the Natoms in O–H···N hydrogen bonding immediately suggeststhe possibility of the formation of weaker hydrogen bonds.9
Indeed the second N atom interacts with a C–H group andforms a C–H···N hydrogen bond. The N atom that acceptsthe O–H···N bond also accepts a C–H···N, and thereforethere are two C–H···N bonds given in Table 2. It is essentialto analyse complex 1 beyond these obvious hydrogen bondpatterns to understand its intricate structural features whichare displayed in Fig. 1a–c.
It is convenient to dissect the crystal packing of 1 into threeroughly orthogonal directions which may be depicted with(non-crystallographic) x, y and z axes (Fig. 1a). The abovedescribed O–H···N/C–H···N hydrogen bonds between HQand phenazine molecules govern the molecular assemblyalong the x-axis leading to a kind of tape structure (Fig. 1b).Adjacent tapes along the z-axis may be said to form a two-dimensional network in which phenazine molecules formcontinuous stacks (stacking separations: 3.442/3.714 and3.517/3.737 Å)10 and the HQ molecules are connected byedge-to-edge C–H···O hydrogen bonded dimers.11 The HQand phenazine molecules are inclined at 85°. Packing in thethird direction, that is along the y-axis, may now beconsidered. The short edges of phenazine molecules aredirected at the faces of HQ molecules in this directionleading to the formation of C–H···O hydrogen bonds andedge-to-face (or C–H···π)12 aromatic interactions (Fig. 1c).
DOI: 10.1039/b003788p
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Table 1 Crystal data and measurement details for 1, 3 and 4
1 3 4
Emp. formula (C12H8N2)2·C6H6O2 (C12H8N2)2·C10H8O2 (C12H8N2)3·C12H10O2
Formula wt. 470.52 520.57 726.81T/K 298 298 298Crystal system Triclinic Triclinic TriclinicSpace group 1P 1P 1Pa/Å 7.286(2) 7.3415(6) 9.2844(4)b/Å 9.004(2) 9.5933(8) 9.4909(5)c/Å 9.239(2) 10.1204(8) 10.7853(5)α/° 77.42(1) 87.680(2) 76.669(1)β/° 74.83(3) 70.207(2) 87.181(1)γ/° 86.326(9) 79.333(2) 82.234(1)Z 1 1 1V/Å3 571.0(3) 658.88(9) 916.12(8)N-totala 2514 5105 7154N-indep.b 1997 2208 3091Rint 0.014 0.058 0.021R1 0.039 0.061 0.060wR2 0.095 0.133 0.171a Number of reflections collected. b Number of independent reflections. Click here for full crystallographic data(CCDC no. 1350/22).
Table 2 Geometrical parameters for various intermolecular interactions in 1, 3 and 4
Complex Interaction H···A/Åa D···A/Å D–H···A/° Directionb
1 O–H···N 1.84 2.815 172 xC–H···N 2.64 3.542 140 xC–H···N 2.64 3.424 129 xC–H···O 2.42 3.441 156 yC–H···O 2.45 3.481 159 yC–H···πc 3.04 3.829 130 (24) yC–H···O 2.95 4.021 170 z
3 O–H···N 1.85 2.824 171 xC–H···N 2.51 3.378 137 xC–H···N 2.69 3.477 129 xC–H···O 2.76 3.839 174 yC–H···O 2.95 3.683 125 yC–H···πc 2.73 3.559 133 (13) yC–H···πc 2.79 3.705 142 (18) yC–H···O 2.55 3.428 137 z
4 O–H···N 1.84 2.824 177 xC–H···N 2.46 3.468 155 xC–H···N 2.58 3.496 142 xC–H···N 2.69 3.472 129 xC–H···O 2.79 3.743 146 yC–H···O 2.87 3.921 163 yC–H···O 2.95 3.680 125 yC–H···πc 2.76 3.555 130 (20) yC–H···πc 2.81 3.640 133 (19) yC–H···O 2.58 3.648 171 z
a The O–H and C–H bond lengths are normalised to standard neutron distances. b The direction along which aninteraction is formed. c The parameters are calculated to the ring centroid. The angle between H···centroid vector andthe acceptor plane is also given in parentheses in the D–H···A column.
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Fig. 1 Crystal packing of complex 1 dissected into the (non-crystallographic) x, y and z axes. (a) View down the z-axis: noticethe arrangement of the phenazine stacks on a square-grid and thechannels thus formed. Note that the HQ molecules are oriented in aperpendicular manner within the channels. Hydrogen bonds are notdrawn for clarity. (b) View down the y-axis: notice the O–H···N/C–H···N tapes along the x-axis and, the phenazine stacks and C–H···Odimers of HQ along the z-axis. (c) View down the x-axis: noticethe C–H···O and edge-to-face (C–H···π) interactions along the y-axis. Click images or here to view the 3D crystal structure of 1.
Alternatively, the structure of 1 may be viewed as formingfrom the juxtaposition of phenazine stacks on a square gridwith HQ molecules filling the channels thus formed. It maythen be envisaged that phenazine forms a host network intowhich HQ molecules enter as guests. In this context it ispertinent to compare the structure of 1 with that of the 3 : 1complex (2) between phenazine and DHP which has beenrecently published.7 The structure of 2 is displayed in Fig.2a–c and its overall similarity to the structure of 1 may beeasily noted. Both of the structures (1 and 2) consist of thehost network made of phenazine stacks, with the donormolecules located in the channels in a perpendicularinclination with respect to the phenazine molecules. Itshould be noted that not all complexes of phenazine with
Fig. 2 Crystal packing of complex 2 dissected into the (non-crystallographic) x, y and z axes. (a) View down the z-axis: noticethe arrangement of phenazine stacks on a square-grid and thechannels thus formed. Note that the DHP molecules are oriented ina perpendicular manner within the channels. Hydrogen bonds arenot drawn for clarity. (b) View down the y-axis: notice the N–H···N/C–H···N tapes along the x-axis and phenazine stacks alongthe z-axis. (c) View down the x-axis: notice the edge-to-facearrangement along the y-axis. Compare the equivalent parts in Fig.1 and 2 and notice the similarities. The structure of 2 has beenpublished recently.7
hydrogen bond donor molecules possess a similar structure.For example, the 3 : 2 complex of phenazine with 2,2´-dihydroxybiphenyl has an entirely different structure.6
From the analysis of the structures of 1 and 2 it may bereasoned that the similarities between these two structuresarise due to the combination of the following effects: (a)the HQ and DHP molecules are bis-hydrogen bond donors,(b) the hydrogen bonding OH or NH groups are positionedin an antiparallel manner, and (c) the HQ and DHPmolecules are aromatic and flat.13
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In order to test the validity of the above reasoning we havedecided to vary the donor molecules while maintaining thefactors involved in the above three effects. We planned thevariation in two ways, viz. (a) to expand (or widen) and (b)to elongate the HQ moiety. Thus we have chosen 1,5-dihydroxynaphthalene (DHN) and 4,4´-dihydroxybiphenyl(DHBP) as expanded and elongated variants of HQ,respectively. We believe that these variations are largeenough to test the robustness of the host framework.
Fig. 3 Crystal packing of complex 3 dissected into the (non-crystallographic) x, y and z axes. (a) View down the z-axis: noticethe arrangement of phenazine stacks on a square-grid and thechannels thus formed. Note that the DHN molecules are oriented ina perpendicular manner within the channels. Hydrogen bonds arenot drawn for clarity. (b) View down the y-axis: notice the O–H···N/C–H···N tapes along the x-axis and, phenazine stacks and C–H···O dimers of DHN along the z-axis. (c) View down the x-axis:notice the C–H···O and edge-to-face (C–H···π) interactions alongthe y-axis. Compare the equivalent parts in Fig. 1, 2 and 3 andnotice the similarities and also slight variations. Click images orhere to view the 3D crystal structure of 3.
Complexation experiments of DHN and DHBP withphenazine have been carried out. While phenazine–DHNassembly leads to a 2 : 1 complex (3), a 3 : 1 complex (4)results from phenazine–DHBP assembly. Single crystals of3 (mp 253–254 °C) and 4 (mp 199–201 °C) suitable for X-ray diffraction analysis were grown from acetone solutionscontaining equimolar quantities of the constituents. Thecrystal structures of complexes 3 and 4 (Table 1) are shownin Fig. 3a–c and 4a–c respectively, and their packingpatterns are also dissected into mutually perpendicular(non-crystallographic) x, y and z axes. The O–H···N/C–H···N assembly in complex 3 is similar to that observed incomplex 1, and generates a tape structure along the x-axis(Fig. 3b). Again the aggregation of these tapes along the z-axis leads to a two-dimensional network wherein thephenazine molecules form continuous stacks (stackingparameters: 3.429/3.912 and 3.506/3.807 Å) and DHNmolecules are related by C–H···O hydrogen bonded dimers.However the pattern of C–H···O dimer in 3 is slightlydifferent from that seen in 1 and the inclination between theDHN and phenazine molecules is 70° (related value incomplex 1 is 85°). The packing in the third direction (alongthe y-axis, Fig. 3c) is governed by edge-to-face (or C–H···π)and C–H···O interactions. While C–H···π interactions areshorter in 3 the C–H···O bonds are shorter in 1 (Table 2) inthis direction. This is because the DHN molecule is widerand π-electron rich compared to the HQ molecule. Despitethese minor packing differences between 1 and 3, a viewdown the z-axis clearly indicates their overall packingsimilarity (Fig. 1a and 3a).
The similarity between complexes 1 and 3 is indicated at agross level by their 2 : 1 stoichiometry. Complex 4 on theother hand contains the constituents in 3 : 1 proportionssuggesting some essential differences in its packing. Indeedcomplex 4 is distinct from complexes 1 and 3 in itshydrogen bond networks.14 In 4, the DHBP molecule andone of the two symmetry independent molecules ofphenazine are located on inversion centres and areconnected by O–H···N hydrogen bonds to generate aninfinite, linear O–H···N bonded array. This is in contrast tothe discrete O–H···N assembly seen in complexes 1 and 3.The second phenazine molecule is located on a generalposition and both of its N atoms form C–H···N hydrogenbonds with the C–H groups of DHBP molecule.Notwithstanding the differences in hydrogen bondnetworks, the structure of 4 can be dissected into (non-crystallographic) x, y and z directions as in 1 and 3.
The pattern of O–H···N and C–H···N interactions describedabove is such that each DHBP molecule is linked to sixphenazine molecules (two through O–H···N and fourthrough C–H···N). The O–H···N/C–H···N assembly may besaid to generate a tape structure along the x-axis (Fig. 4b).These tapes aggregate along the z-axis (as in 1 and 3) andgenerate a two-dimensional network within which thephenazine molecules form continuous stacks (stackingparameters: 3.42/3.74 and 3.39/3.83 Å) and DHBPmolecules are related by C–H···O hydrogen bonded dimers.The C–H···O dimer pattern is similar to that in 1. TheDHBP molecule is inclined with respect to the twosymmetry independent phenazine molecules at 71 and 73°(cf. 85 and 70° in 1 and 3). Edge-to-face (or C–H···) and C–H···O interactions contribute to the packing in the thirddirection (along the y-axis, Fig. 4c). As in complex 3 theC–H··· interactions are shorter than C–H···O bridges incomplex 4 (Table 2). A view down the z-axis (Fig. 4a)shows the structural similarity between complexes 1–4.
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Fig. 4 Crystal packing of complex 4 dissected into the (non-crystallographic) x, y and z axes. (a) View down the z-axis: noticethe arrangement of phenazine stacks on a square-grid and thechannels thus formed. Note that the DHBP molecules are orientedin a perpendicular manner within the channels. Hydrogen bondsare not drawn for clarity. (b) View down the y-axis: notice the O–H···N/C–H···N tapes along the x-axis and, phenazine stacks and C–H···O dimers of DHBP along the z-axis. (c) View down the x-axis:notice the C–H···O and edge-to-face (C–H···π) interactions alongthe y-axis. Compare the equivalent parts in Fig. 1–4 and notice thesimilarities and also slight variations. Click images or here to viewthe 3D crystal structure of 4.
We shall now look at the phenazine host frameworks in 1–4. In all of the cases the phenazine stacks may be imaginedto be located on a two-dimensional square-grid. The griddimensions vary slightly from complex to complex and arein the range of 9–10 Å (the distance between two nearestgrid points) and 80–100° (the angle between three nearestgrid points). In all of these cases the phenazine moleculesin the adjacent stacks are in parallel planes.15 The edges ofone phenazine molecule are fitted into the edges of aneighbouring molecule on this grid, and the phenazine
stacks are sustained by these edge-to-edge aromaticcontacts. We may now look at the host–guest interactions.While the essential interactions between the phenazineframework and the guest molecules are the same in all thestructures, there are some minor but non-insignificantdifferences within the interaction patterns. For example,while the dimer pattern of C–H···O bonds along the z-axisis similar for HQ and DHBP (in 1 and 4), it is different forDHN (in 3). These differences arise as a consequence of theoptimisation of weak interactions (C–H···O, C–H···N andC–H···π).
ConclusionA comparison of complexes 1–4 reveals that the hostarchitecture of phenazine is robust (in that it is alwaysformed) and also flexible (in that stacking distances, gridseparations and mutual inclinations between phenazinemolecules are varied). These complexes illustrate that thewidth and length of the guests can be varied at will,provided these variations take into account that theresultant guest molecule (a) is a bis donor with two donorgroups in anti-parallel orientation (to ensure the hydrogenbond connections with phenazine stacks along the x-axis)and (b) is also flat and π-electron rich (to ensure the C–H···π interactions along the y-axis). In addition, C–H···Nhydrogen bonds play a key role in the supramolecularassembly along the x-axes in complexes 1–4.Reproducibility is a key feature in crystal engineering16 andconsistent formation of phenazine molecular stacks incomplexes 1–4, despite significant variations in the guests,suggests that these stacks can be used in the reliable designof desired structures. If non-centrosymmetry can beintroduced into the phenazine based host–guest architecture(e.g., by selecting a non-centrosymmetric guest) this couldhave potential applications in non-linear optics.17
AcknowledgementsThis work was supported by the DeutscheForschungsgemeinschaft (SFB-452) and the Fonds derChemischen Industrie. VRT thanks the Alexander vonHumboldt foundation for a post-doctoral fellowship.
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Boese, J. Prakt. Chem., 2000, 342, in the press.9 G. R. Desiraju and T. Steiner, Weak Hydrogen Bond in
Structural Chemistry and Biology, Oxford UniversityPress, Oxford, 1999.
10 For π-stacking interactions the geometrical parametersare given as the interplanar distance + the distancebetween the centroids. In all of the stacking interactionsreported in this work the interplanar angles are in therange 0 to 2°.
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11 (a) C. E. Marjo, M. L. Scudder, D. C. Craig and R.Bishop, J. Chem. Soc., Perkin Trans. 2, 1997, 2029; (b)V. T. Nguyen, A. N. M. M. Rahman, R. Bishop, D. C.Craig and M. Scudder, Aust. J. Chem., 1999, 52, 1047.
12 M. Nishio, M. Hirota and Y. Umezawa, The CH/Interaction: Evidence, Nature and Consequences,Wiley-VCH, New York, 1998.
13 The two OH groups in 2,2´-dihydroxybiphenyl are notin an anti-parallel disposition and therefore thestructure of its complex with phenazine (ref. 6) isdifferent from those of 1 and 2.
14 Complex 4 is similar to complex 2 in many respects forthe same reason (3 : 1 stoichiometry).
15 A similar phenazine host network exists in the crystalstructure of the 1 : 1 complex between phenazine andoxalic acid (ref. 8). However, the phenazine moleculesin adjacent stacks are inclined at 27°.
16 G. R. Desiraju, Angew. Chem., Int. Ed. Engl., 1995, 34,2311.
17 J. Hulliger, P. J. Langley, O. Konig, S. W. Roth, A.Quintel and P. Rechsteiner, Pure Appl. Opt., 1998, 7,221.
CrystEngComm © The Royal Society of Chemistry 2000
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