Dalton Transactions Published on 16 October 2013. Downloaded by Universitat Politècnica de València on 25/10/2014 12:28:32.
COMMUNICATION
Cite this: Dalton Trans., 2013, 42, 16474 Received 21st May 2013, Accepted 2nd October 2013 DOI: 10.1039/c3dt51330k
View Article Online View Journal | View Issue
Towards a self-assembled honeycomb structure via diaminotriptycene metal complexes† Qian Liang,a,b Jonathan H. Chong,a Nicholas G. White,a Zhen Zhaob and Mark J. MacLachlan*a
www.rsc.org/dalton
We illustrate a new approach toward the synthesis of a porous supramolecular honeycomb based on triptycene. A coordination polymer has been prepared where the triptycene groups are linked through triptycenesemiquinonediimine platinum complexes, but the product is disordered rather than the intended honeycomb structure. A model platinum complex and its 15 N-labeled isotopomer have been prepared and characterized.
Introduction Diverse porous materials assembled from molecules have been reported recently, especially for gas storage, catalysis, and energy-related applications.1,2 By employing molecular components, the structures may be tuneable and even somewhat predictable.3 For example, a large family of isoreticular metal– organic frameworks can be constructed from zinc salts and aromatic linkers functionalized with carboxylic acid groups.4 Triptycene (1) is a molecule with three aromatic rings connected to two bridgehead carbon atoms, giving overall D3h symmetry to the molecule. The shape of this molecule leaves space between the rings that has been termed “internal free volume” and may lead to highly porous structures in the solid state. Indeed, there has been considerable interest in exploiting this component for the construction of porous polymers,5 porous molecules,6 metal–organic frameworks,7 and other materials.8 Recently, Mastalerz reported a hydrogen-bonded assembly of functionalized triptycene molecules with recordsetting surface areas and gas storage capacity for a molecular solid.9 a Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, Canada V6T 1Z1. E-mail: [email protected]; Fax: +1 604 822 2847; Tel: +1 604 822 3070 b State Key Lab of Heavy Oil Processing, China University of Petroleum, 18 Fuxue Road, Changping, Beijing 102249, P. R. China † Electronic supplementary information (ESI) available: Details of the crystallography, 1H and 13C NMR spectra of new compounds, and additional characterization. CCDC 940143. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3dt51330k
16474 | Dalton Trans., 2013, 42, 16474–16477
Honeycomb lattices are hexagonal structures with interior angles of 120°. Many substances are known to form open 2-D hexagonal structures in the solid state or on surfaces.10 As the angles between the planes of aromatic rings in triptycene are also 120°, triptycene is an attractive component for constructing honeycomb networks. However, finding a motif that will allow for the triptycenes to link into a honeycomb lattice has proven to be a challenge. A linker that can connect two aromatic rings of different triptycene molecules into the same plane is required. McKeown and co-workers have exploited nucleophilic aromatic substitution to afford crosslinked polymer networks that have a disordered honeycomb structure based on the component 2.11 Zonta et al. formed a triptycene trimaleimide, but found that the molecules are not aligned into a honeycomb structure as predicted.12 We previously investigated quinoxalines (e.g., 3) as bridging groups between triptycenes in order to connect the molecules into honeycomb lattices.13 However, the irreversibility of the quinoxaline formation coupled with the low yield from coupling in model compounds prevented the formation of a network.
Thus, we believe that the best way to construct a porous honeycomb lattice by design from triptycene derivatives may be to
This journal is © The Royal Society of Chemistry 2013
View Article Online
Dalton Transactions
Communication
Published on 16 October 2013. Downloaded by Universitat Politècnica de València on 25/10/2014 12:28:32.
exploit coordination chemistry. Here we describe our efforts to construct a porous honeycomb lattice from polyaminotriptycene and metal salts. Importantly, we have discovered a new motif for connecting triptycenes together that may allow for the development of hexagonal macrocycles and honeycomb structures based on triptycene.
Results and discussion Diaminotriptycene 4 and hexaaminotriptycene 5 are readily synthesized from triptycene.13,14 If 5 could complex to transition metals in square planar geometry, thus connecting two aromatic rings of triptycene in the same plane, this could be a means to construct a honeycomb lattice. Before making the honeycomb lattice, we first set out to synthesize model compounds that would allow us to establish the correct conditions for obtaining the complexes and also to study the structural aspects of the molecules. Reaction of 4 with K2PtCl4 afforded compound 6 in 36% yield (Scheme 1). Compound 6 is a blue solid, and its UVvisible spectrum shows an intense peak at 753 nm that corresponds to a ligand-to-ligand charge transfer (LLCT) band.15 The MALDI-TOF mass spectrum showed the molecular ion at m/z = 758.4 Da, and had nearly the isotope distribution expected for the product. An important question for us was the nature of the coordination environment around the platinum – o-phenylenediimine is a non-innocent ligand whose identity is often confused.16 We naively expected that the triptycenediamine groups in 6 were each singly deprotonated to give amino–amido bidentate ligands. However, the mass spectrum of the complex indicated a mass that only matched 6 with four N–H protons. As well, 1H NMR spectroscopy of 6 showed only a single N–H environment (at 7.81 ppm in DMSO-d6) and it integrated to exactly one H atom per N. Upon reviewing the literature, it appears that phenylenediamine complexes of platinum17 and other metals16,18 may form o-semibenzoquinonediimine (s-bqdi) complexes. This is indeed what we observe in 6. As further evidence of the s-bqdi structure in 6, we formed 6 from compound 4 that has one 14NH2 and one 15NH2 group.
Scheme 1
Synthesis of complex 6.
This journal is © The Royal Society of Chemistry 2013
In the 1H NMR spectrum of 6-15N2, the resonance at 7.81 ppm (NH) is split into a singlet (from 14NH) and a doublet (from 15 NH) in a 1 : 1 ratio, as expected for the s-bqdi form. 1J15N–1H is 74.5 Hz, clearly indicative of one-bond coupling. We were unable to find coupling constants measured for other s-bqdi compounds for comparison. The single-crystal structure of 6‡ (Fig. 1) shows the expected square planar geometry at the metal center that is consistent with the structure previously obtained for the parent o-phenylenediamine complex, (s-bqdi)2Pt.17 There is a center of inversion in the molecule that lies on the Pt atom. Pt–N distances in 6 (1.951(4), 1.957(4) Å) compare well to distances of 1.96 Å determined in (s-bqdi)2Pt. Other bond distances within the aromatic rings closest to the Pt2+ ion in 6 are also consistent with the o-semibenzoquinonediimine structure. Hydrogen atoms attached to N were located in difference maps. The solid-state packing of 6 shows the influence of triptycenes on decreasing the packing efficiency, leading to the formation of solvent-filled channels extending along the direction of the a-axis (Fig. 1b); these channels separate the layers composed of molecules of 6 (Fig. 1c). There are no close Pt⋯Pt contacts; the closest separations are over 8 Å. We expected that the analogous complex to 6 with Cu2+ could be obtained by reacting 4 with Cu(OAc)2. Indeed we obtained a copper complex that showed the expected mass. However, efforts to grow single crystals of the copper complex were not fruitful and we found its stability to be relatively poor in solution compared with 6. Unsure of the geometry at the metal center in this copper complex, we focused our attention on the Pt complexes. From these results, diaminotriptycene clearly forms square planar complexes with Pt(II) and would therefore be appropriate as the linker to form a honeycomb network starting with hexaaminotriptycene 5. We first reacted hexaaminotriptycene with K2PtCl4 in methanol at reflux (70 °C) for 15 h (the same conditions used to prepare complex 6) and obtained a black
Fig. 1 Solid-state structure of 6 as determined by SCXRD. Hydrogen atoms have been omitted for clarity. (a) ORTEP of the single molecule. Ellipsoids are shown at 50% probability. Carbon, black; nitrogen, blue; platinum, brown. (b) View along a-axis (DMSO molecules shown in green). (c) View along b-axis (DMSO molecules shown in green).
Dalton Trans., 2013, 42, 16474–16477 | 16475
View Article Online
Published on 16 October 2013. Downloaded by Universitat Politècnica de València on 25/10/2014 12:28:32.
Communication powder ( product 7). X-ray diffraction of the product (Fig. S7†) showed that Pt was the only crystalline species present, and from linewidth analysis, the Pt particles are about 50 nm in diameter (calculated for 2θ = 39.9° (111) using the Scherrer equation). Transmission electron microscopy (Fig. S8†) revealed a high population of Pt nanoparticles with diameters of ∼20 nm along with larger agglomerate particle ensembles. Compared with diaminotriptycene, the higher reducing ability of hexaaminotriptycene enables the reduction of Pt2+ to Pt0, thus forming Pt nanoparticles under the same conditions used to synthesize compound 6. Clearly the elevated temperature was the problem and led to the degradation of the product with release of Pt nanoparticles. The procedure was then repeated at room temperature, yielding a dark purple solid. The product 8 was insoluble in organic solvents and water, consistent with an extended structure. We analyzed the product by several techniques to deduce its chemical composition and structure. Fig. 2 depicts the idealized target honeycomb structure with predicted dimensions based on the crystal structure of 6. Elemental analysis of 8 was reasonably close to the theoretical value for the honeycomb structure, accounting for encapsulated solvent. The XPS wide scan spectrum (see ESI†) showed characteristic signatures for C 1s, Pt 4f, N 1s and O 1s lines, which are in good agreement with the chemical formula of 8; no peaks for Cl or K were observed. In the high resolution spectra, the Pt 4f5/2 and Pt 4f7/2 peaks are observed at 76.6 and 73.5 eV, respectively, which are typical values for Pt2+ complexes. XPS analysis is very sensitive to any change of chemical structure or valence state. The observed Pt XPS spectra of 8 are nearly identical to 6 (Pt 4f5/2 = 76.7 eV and Pt 4f7/2 = 73.5 eV), indicating the Pt2+ species in 6 and 8 are in the same chemical environment. Thus, XPS data support the proposed (s-bqdi)2Pt connectivity between the triptycene groups in 8.
Dalton Transactions We estimated that the hypothetical honeycomb lattice shown in Fig. 2 should be made up of hexagons with edge length of 13.06 Å (from the crystal structure of 6), yielding a hexagonal unit cell with dimensions of a = 22.65 Å, and would be expected to show a (100) reflection at ∼19.6 Å d-spacing. Unfortunately, the PXRD pattern of 8 showed no features, suggesting that the product must be substantially disordered. 13 C CP-MAS NMR spectroscopy of 8 showed only a relatively broad, featureless peak centered around 140 ppm, also consistent with a disordered product. Scanning electron microscopy (SEM) showed that 8 is comprised of uniform spherical-like particles with an average diameter of 0.24 μm. Transmission electron microscopy (TEM) of 8 revealed the solid structures with a diameter of 0.25 μm in accord with morphology observed by SEM. We can see a disordered porous texture from the solid and pore sizes less than 2 nm. The porosity of 8 was measured by N2 sorption experiments. In our first attempts, we dried the sample at 120 °C under vacuum overnight, but measured no significant adsorption of nitrogen at 77 K. It is likely that Pt NPs begin to form at 120 °C and may facilitate collapse of the structure (PXRD did not show large particles, but there were significant changes to the IR spectrum of the materials). We found that it was best to exchange solvent in order to maintain a porous structure. We first stirred the sample with ethanol (60 h total, changing the ethanol every 12 h) and then with hexanes (60 h total, changing the hexanes every 12 h). The powder was collected by centrifugation and degassed under vacuum for 48 h at 50 °C. Following this procedure, we found that 8 had substantial porosity.19 The isotherm for 8 is best classified as Type II isotherm, showing a steep slope below P/P0 = 0.10 (Fig. S12†). The BET-model surface area is 695(8) m2 g−1 and Langmuir-model surface area is 932(8) m2 g−1. From the t-plot analysis, the micropore volume is 0.17 cm3 g−1 and micropore area is 384 m2 g−1, a micropore contribution of 55% of overall surface area. To the best of our knowledge, this one of the highest surface areas of a platinum coordination polymer.
Conclusions
Fig. 2 Depiction of the target honeycomb coordination network that would be obtained from reacting hexaaminotriptycene 5 with K2PtCl4. The structure of 6, which represents a fragment of the honeycomb lattice, is shown on the top left to indicate the dimensions of an edge.
16476 | Dalton Trans., 2013, 42, 16474–16477
In summary, we describe a new concept for constructing a porous honeycomb lattice based on triptycene, where metal coordination is used to link them into a hexagonal structure. We have made the first metal complex of o-triptycenesemiquinonediimine and verified its structure by many techniques, including a 15N labelling experiment. By replacing diaminotriptycene with hexaaminotriptycene, a porous, insoluble coordination polymer based on triptycene was formed. The lack of significant X-ray diffraction from the material suggests that the structure is disordered. Nonetheless, this new approach to linking triptycene groups using benzenesemiquinonediimine motifs is a promising way to assemble molecular hexagons and extended honeycomb structures, and we are continuing to pursue these goals.
This journal is © The Royal Society of Chemistry 2013
View Article Online
Dalton Transactions
Acknowledgements
Published on 16 October 2013. Downloaded by Universitat Politècnica de València on 25/10/2014 12:28:32.
We thank NSFC (21073235, 21177160) and NSERC for funding. NGW thanks the Killam Foundation for a Post-doctoral Fellowship.
Notes and references ‡ Crystal data for 6: Monoclinic, space group: P21/c, a = 11.8563(9) Å, b = 8.1225(5) Å, c = 23.6634(17) Å, α = γ = 90°, β = 93.544(3)°, V = 2274.5(3) Å3, Z = 2, T = 173 K, F(000) = 916, ρcalcd = 1.34 g cm−3, μ(Mo Kα) = 3.213 mm−1 (λ = 0.71073 Å), 41 855 measured reflections, 4676 independent reflections (Rint = 0.0316), 256 refined parameters, R1 = 0.0372 for I > 2σ(I), and wR2 = 0.0987, GOF = 1.084.
1 C. M. A. Parlett, K. Wilson and A. F. Lee, Chem. Soc. Rev., 2013, 42, 3876; D. Wu, F. Xu, B. Sun, R. Fu, H. He and K. Matyjaszewski, Chem. Rev., 2012, 112, 3959; J. Tian, P. K. Thallapally and B. P. McGrail, CrystEngComm, 2012, 14, 1909; D. Bradshaw, J. B. Claridge, E. J. Cussen, T. J. Prior and M. J. Rosseinsky, Acc. Chem. Res., 2005, 38, 273. 2 Recent activity: J. T. A. Jones, T. Hasell, X. Wu, J. Bacsa, K. E. Jelfs, M. Schmidtmann, S. Y. Chong, D. J. Adams, A. Trewin, F. Schiffman, F. Cora, B. Slater, A. Steiner, G. M. Day and A. I. Cooper, Nature, 2011, 474, 367; C. G. Bezzu, M. Helliwell, J. E. Warren, D. R. Allan and N. B. McKeown, Science, 2010, 327, 1627; Z. Xiang and D. Cao, J. Mater. Chem. A, 2013, 1, 2691; C. Tedesco, L. Erra, M. Brunelli, V. Cipolletti, C. Gaeta, A. N. Fitch, J. L. Atwood and P. Neri, Chem.–Eur. J., 2010, 16, 2371; J. Tian, S. Ma, P. K. Thallapally, D. Fowler, B. P. McGrail and J. L. Atwood, Chem. Commun., 2011, 47, 7626. 3 T. Tozawa, J. T. A. Jones, S. I. Swamy, S. Jiang, D. J. Adams, S. Shakespeare, R. Clowes, D. Bradshaw, T. Hasell, S. Y. Chong, C. Tang, S. Thompson, J. Parker, A. Trewin, J. Basca, A. M. Z. Slawin, A. Steiner and A. I. Cooper, Nat. Mater., 2009, 8, 973; G. Férey, Chem. Soc. Rev., 2008, 37, 191. 4 J. L. C. Rowsell and O. M. Yaghi, Microporous Mesoporous Mater., 2004, 73, 3; H. Deng, S. Grunder, K. E. Cordova, C. Valente, H. Furukawa, M. Hmadeh, F. Gándara, A. C. Whalley, Z. Liu, S. Asahina, H. Kazumori, M. O’Keeffe, O. Terasaki, J. F. Stoddart and O. M. Yaghi, Science, 2012, 336, 1018. 5 B. S. Ghanem, K. J. Msayib, N. B. McKeown, K. D. M. Harris, Z. Pan, P. M. Budd, A. Butler, J. Selbie, D. Book and A. Walton, Chem. Commun., 2007, 67; J.-S. Yang and T. M. Swager, J. Am. Chem. Soc., 1998, 120, 5321; T. M. Swager, Acc. Chem. Res., 2008, 41, 1181; C. Zhang, Y. Liu, B. Li, B. Tan, C.-F. Chen, H.-B. Xu and X.-L. Yang, ACS Macro Lett., 2012, 1, 190; N. T. Tsui, L. Torun, B. D. Pate, A. J. Paraskos, T. M. Swager and E. L. Thomas, Adv. Funct. Mater., 2007, 17, 1595.
This journal is © The Royal Society of Chemistry 2013
Communication 6 J. H. Chong, S. J. Ardakani, K. J. Smith and M. J. MacLachlan, Chem.–Eur. J., 2009, 15, 11824; M. Mastalerz, M. W. Schneider, I. M. Oppel and O. Presly, Angew. Chem., Int. Ed., 2011, 50, 1046. 7 J. H. Chong and M. J. MacLachlan, Inorg. Chem., 2006, 45, 1442; M. Munakata, L. P. Wu, K. Sugimoto, T. KurodaSowa, M. Maekawa, Y. Suenaga, N. Maeno and M. Fujita, Inorg. Chem., 1999, 38, 5674; X. Roy, J. H. Chong, B. O. Patrick and M. J. MacLachlan, Cryst. Growth Des., 2011, 11, 4551; S. Vagin, A. Ott, H.-C. Weiss, A. Karbach, D. Volkmer and B. Rieger, Eur. J. Inorg. Chem., 2008, 16, 2601; S. I. Vagin, A. K. Ott, S. D. Hoffmann, D. Lanzinger and B. Rieger, Chem.–Eur. J., 2009, 15, 5845; C.-H. Lee, R. Filler, J. Lee, J. Li and B. K. Mandal, Renewable Energy, 2010, 35, 1592; A. K. Crane, B. O. Patrick and M. J. MacLachlan, Dalton Trans., 2013, 42, 8026. 8 J. H. Chong and M. J. MacLachlan, Chem. Soc. Rev., 2009, 38, 3301; C.-F. Chen, Chem. Commun., 2011, 47, 1674. 9 M. Mastalerz and I. M. Oppel, Angew. Chem., Int. Ed., 2012, 51, 5252. 10 J. W. Colson, A. R. Woll, A. Mukherjee, M. P. Levendorf, E. L. Spitler, V. B. Shields, M. G. Spencer, J. Park and W. R. Dichtel, Science, 2011, 332, 228; C. J. Doonan, D. J. Tranchemontagne, T. G. Glover, J. R. Hunt and O. M. Yaghi, Nat. Chem., 2010, 2, 235; K. M. Ok, J. Sung, G. Hu, R. M. J. Jacobs and D. O’Hare, J. Am. Chem. Soc., 2008, 130, 3762; M. Lackinger, S. Griessl, W. M. Heckl, M. Hietschold and G. W. Flynn, Langmuir, 2005, 21, 4984. 11 B. S. Ghanem, M. Hashem, K. D. M. Harris, K. J. Msayib, M. Xu, P. M. Budd, N. Chaukura, D. Book, S. Tedds, A. Walton and N. B. McKeown, Macromolecules, 2010, 43, 5287. 12 C. Zonta, O. De Lucchi, A. Linden and M. Lutz, Molecules, 2010, 15, 226. 13 J. H. Chong and M. J. MacLachlan, J. Org. Chem., 2007, 72, 8683. 14 M. Mastalerz, S. Sieste, M. Cenić and I. M. Oppel, J. Org. Chem., 2011, 76, 6389. 15 P. Chaudhury, C. N. Verani, E. Bill, E. Bothe, T. Weyhermüller and K. Wieghardt, J. Am. Chem. Soc., 2001, 123, 2213. 16 D. Herebian, E. Bothe, F. Neese, T. Weyhermüller and K. Wieghardt, J. Am. Chem. Soc., 2003, 125, 9116. 17 Y. Konno and N. Matsushita, Bull. Chem. Soc. Jpn., 2006, 79, 1046; Y. Konno and N. Matsushita, Bull. Chem. Soc. Jpn., 2006, 79, 1237; T. Koizumi and K. Fukuju, J. Organomet. Chem., 2011, 696, 1232. 18 K. Chłopek, E. Bothe, F. Neese, T. Weyhermüller and K. Wieghardt, Inorg. Chem., 2006, 45, 6298; G. Ricciardi, A. Rosa, G. Morelli and F. Lelj, Polyhedron, 1991, 10, 955. 19 Sorption measurement of multiple samples gave surface areas in the range of ∼150–700 m2 g−1; the data presented are for one of the best samples.
Dalton Trans., 2013, 42, 16474–16477 | 16477
COMMUNICATION
Cite this: Dalton Trans., 2013, 42, 16474 Received 21st May 2013, Accepted 2nd October 2013 DOI: 10.1039/c3dt51330k
View Article Online View Journal | View Issue
Towards a self-assembled honeycomb structure via diaminotriptycene metal complexes† Qian Liang,a,b Jonathan H. Chong,a Nicholas G. White,a Zhen Zhaob and Mark J. MacLachlan*a
www.rsc.org/dalton
We illustrate a new approach toward the synthesis of a porous supramolecular honeycomb based on triptycene. A coordination polymer has been prepared where the triptycene groups are linked through triptycenesemiquinonediimine platinum complexes, but the product is disordered rather than the intended honeycomb structure. A model platinum complex and its 15 N-labeled isotopomer have been prepared and characterized.
Introduction Diverse porous materials assembled from molecules have been reported recently, especially for gas storage, catalysis, and energy-related applications.1,2 By employing molecular components, the structures may be tuneable and even somewhat predictable.3 For example, a large family of isoreticular metal– organic frameworks can be constructed from zinc salts and aromatic linkers functionalized with carboxylic acid groups.4 Triptycene (1) is a molecule with three aromatic rings connected to two bridgehead carbon atoms, giving overall D3h symmetry to the molecule. The shape of this molecule leaves space between the rings that has been termed “internal free volume” and may lead to highly porous structures in the solid state. Indeed, there has been considerable interest in exploiting this component for the construction of porous polymers,5 porous molecules,6 metal–organic frameworks,7 and other materials.8 Recently, Mastalerz reported a hydrogen-bonded assembly of functionalized triptycene molecules with recordsetting surface areas and gas storage capacity for a molecular solid.9 a Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, Canada V6T 1Z1. E-mail: [email protected]; Fax: +1 604 822 2847; Tel: +1 604 822 3070 b State Key Lab of Heavy Oil Processing, China University of Petroleum, 18 Fuxue Road, Changping, Beijing 102249, P. R. China † Electronic supplementary information (ESI) available: Details of the crystallography, 1H and 13C NMR spectra of new compounds, and additional characterization. CCDC 940143. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3dt51330k
16474 | Dalton Trans., 2013, 42, 16474–16477
Honeycomb lattices are hexagonal structures with interior angles of 120°. Many substances are known to form open 2-D hexagonal structures in the solid state or on surfaces.10 As the angles between the planes of aromatic rings in triptycene are also 120°, triptycene is an attractive component for constructing honeycomb networks. However, finding a motif that will allow for the triptycenes to link into a honeycomb lattice has proven to be a challenge. A linker that can connect two aromatic rings of different triptycene molecules into the same plane is required. McKeown and co-workers have exploited nucleophilic aromatic substitution to afford crosslinked polymer networks that have a disordered honeycomb structure based on the component 2.11 Zonta et al. formed a triptycene trimaleimide, but found that the molecules are not aligned into a honeycomb structure as predicted.12 We previously investigated quinoxalines (e.g., 3) as bridging groups between triptycenes in order to connect the molecules into honeycomb lattices.13 However, the irreversibility of the quinoxaline formation coupled with the low yield from coupling in model compounds prevented the formation of a network.
Thus, we believe that the best way to construct a porous honeycomb lattice by design from triptycene derivatives may be to
This journal is © The Royal Society of Chemistry 2013
View Article Online
Dalton Transactions
Communication
Published on 16 October 2013. Downloaded by Universitat Politècnica de València on 25/10/2014 12:28:32.
exploit coordination chemistry. Here we describe our efforts to construct a porous honeycomb lattice from polyaminotriptycene and metal salts. Importantly, we have discovered a new motif for connecting triptycenes together that may allow for the development of hexagonal macrocycles and honeycomb structures based on triptycene.
Results and discussion Diaminotriptycene 4 and hexaaminotriptycene 5 are readily synthesized from triptycene.13,14 If 5 could complex to transition metals in square planar geometry, thus connecting two aromatic rings of triptycene in the same plane, this could be a means to construct a honeycomb lattice. Before making the honeycomb lattice, we first set out to synthesize model compounds that would allow us to establish the correct conditions for obtaining the complexes and also to study the structural aspects of the molecules. Reaction of 4 with K2PtCl4 afforded compound 6 in 36% yield (Scheme 1). Compound 6 is a blue solid, and its UVvisible spectrum shows an intense peak at 753 nm that corresponds to a ligand-to-ligand charge transfer (LLCT) band.15 The MALDI-TOF mass spectrum showed the molecular ion at m/z = 758.4 Da, and had nearly the isotope distribution expected for the product. An important question for us was the nature of the coordination environment around the platinum – o-phenylenediimine is a non-innocent ligand whose identity is often confused.16 We naively expected that the triptycenediamine groups in 6 were each singly deprotonated to give amino–amido bidentate ligands. However, the mass spectrum of the complex indicated a mass that only matched 6 with four N–H protons. As well, 1H NMR spectroscopy of 6 showed only a single N–H environment (at 7.81 ppm in DMSO-d6) and it integrated to exactly one H atom per N. Upon reviewing the literature, it appears that phenylenediamine complexes of platinum17 and other metals16,18 may form o-semibenzoquinonediimine (s-bqdi) complexes. This is indeed what we observe in 6. As further evidence of the s-bqdi structure in 6, we formed 6 from compound 4 that has one 14NH2 and one 15NH2 group.
Scheme 1
Synthesis of complex 6.
This journal is © The Royal Society of Chemistry 2013
In the 1H NMR spectrum of 6-15N2, the resonance at 7.81 ppm (NH) is split into a singlet (from 14NH) and a doublet (from 15 NH) in a 1 : 1 ratio, as expected for the s-bqdi form. 1J15N–1H is 74.5 Hz, clearly indicative of one-bond coupling. We were unable to find coupling constants measured for other s-bqdi compounds for comparison. The single-crystal structure of 6‡ (Fig. 1) shows the expected square planar geometry at the metal center that is consistent with the structure previously obtained for the parent o-phenylenediamine complex, (s-bqdi)2Pt.17 There is a center of inversion in the molecule that lies on the Pt atom. Pt–N distances in 6 (1.951(4), 1.957(4) Å) compare well to distances of 1.96 Å determined in (s-bqdi)2Pt. Other bond distances within the aromatic rings closest to the Pt2+ ion in 6 are also consistent with the o-semibenzoquinonediimine structure. Hydrogen atoms attached to N were located in difference maps. The solid-state packing of 6 shows the influence of triptycenes on decreasing the packing efficiency, leading to the formation of solvent-filled channels extending along the direction of the a-axis (Fig. 1b); these channels separate the layers composed of molecules of 6 (Fig. 1c). There are no close Pt⋯Pt contacts; the closest separations are over 8 Å. We expected that the analogous complex to 6 with Cu2+ could be obtained by reacting 4 with Cu(OAc)2. Indeed we obtained a copper complex that showed the expected mass. However, efforts to grow single crystals of the copper complex were not fruitful and we found its stability to be relatively poor in solution compared with 6. Unsure of the geometry at the metal center in this copper complex, we focused our attention on the Pt complexes. From these results, diaminotriptycene clearly forms square planar complexes with Pt(II) and would therefore be appropriate as the linker to form a honeycomb network starting with hexaaminotriptycene 5. We first reacted hexaaminotriptycene with K2PtCl4 in methanol at reflux (70 °C) for 15 h (the same conditions used to prepare complex 6) and obtained a black
Fig. 1 Solid-state structure of 6 as determined by SCXRD. Hydrogen atoms have been omitted for clarity. (a) ORTEP of the single molecule. Ellipsoids are shown at 50% probability. Carbon, black; nitrogen, blue; platinum, brown. (b) View along a-axis (DMSO molecules shown in green). (c) View along b-axis (DMSO molecules shown in green).
Dalton Trans., 2013, 42, 16474–16477 | 16475
View Article Online
Published on 16 October 2013. Downloaded by Universitat Politècnica de València on 25/10/2014 12:28:32.
Communication powder ( product 7). X-ray diffraction of the product (Fig. S7†) showed that Pt was the only crystalline species present, and from linewidth analysis, the Pt particles are about 50 nm in diameter (calculated for 2θ = 39.9° (111) using the Scherrer equation). Transmission electron microscopy (Fig. S8†) revealed a high population of Pt nanoparticles with diameters of ∼20 nm along with larger agglomerate particle ensembles. Compared with diaminotriptycene, the higher reducing ability of hexaaminotriptycene enables the reduction of Pt2+ to Pt0, thus forming Pt nanoparticles under the same conditions used to synthesize compound 6. Clearly the elevated temperature was the problem and led to the degradation of the product with release of Pt nanoparticles. The procedure was then repeated at room temperature, yielding a dark purple solid. The product 8 was insoluble in organic solvents and water, consistent with an extended structure. We analyzed the product by several techniques to deduce its chemical composition and structure. Fig. 2 depicts the idealized target honeycomb structure with predicted dimensions based on the crystal structure of 6. Elemental analysis of 8 was reasonably close to the theoretical value for the honeycomb structure, accounting for encapsulated solvent. The XPS wide scan spectrum (see ESI†) showed characteristic signatures for C 1s, Pt 4f, N 1s and O 1s lines, which are in good agreement with the chemical formula of 8; no peaks for Cl or K were observed. In the high resolution spectra, the Pt 4f5/2 and Pt 4f7/2 peaks are observed at 76.6 and 73.5 eV, respectively, which are typical values for Pt2+ complexes. XPS analysis is very sensitive to any change of chemical structure or valence state. The observed Pt XPS spectra of 8 are nearly identical to 6 (Pt 4f5/2 = 76.7 eV and Pt 4f7/2 = 73.5 eV), indicating the Pt2+ species in 6 and 8 are in the same chemical environment. Thus, XPS data support the proposed (s-bqdi)2Pt connectivity between the triptycene groups in 8.
Dalton Transactions We estimated that the hypothetical honeycomb lattice shown in Fig. 2 should be made up of hexagons with edge length of 13.06 Å (from the crystal structure of 6), yielding a hexagonal unit cell with dimensions of a = 22.65 Å, and would be expected to show a (100) reflection at ∼19.6 Å d-spacing. Unfortunately, the PXRD pattern of 8 showed no features, suggesting that the product must be substantially disordered. 13 C CP-MAS NMR spectroscopy of 8 showed only a relatively broad, featureless peak centered around 140 ppm, also consistent with a disordered product. Scanning electron microscopy (SEM) showed that 8 is comprised of uniform spherical-like particles with an average diameter of 0.24 μm. Transmission electron microscopy (TEM) of 8 revealed the solid structures with a diameter of 0.25 μm in accord with morphology observed by SEM. We can see a disordered porous texture from the solid and pore sizes less than 2 nm. The porosity of 8 was measured by N2 sorption experiments. In our first attempts, we dried the sample at 120 °C under vacuum overnight, but measured no significant adsorption of nitrogen at 77 K. It is likely that Pt NPs begin to form at 120 °C and may facilitate collapse of the structure (PXRD did not show large particles, but there were significant changes to the IR spectrum of the materials). We found that it was best to exchange solvent in order to maintain a porous structure. We first stirred the sample with ethanol (60 h total, changing the ethanol every 12 h) and then with hexanes (60 h total, changing the hexanes every 12 h). The powder was collected by centrifugation and degassed under vacuum for 48 h at 50 °C. Following this procedure, we found that 8 had substantial porosity.19 The isotherm for 8 is best classified as Type II isotherm, showing a steep slope below P/P0 = 0.10 (Fig. S12†). The BET-model surface area is 695(8) m2 g−1 and Langmuir-model surface area is 932(8) m2 g−1. From the t-plot analysis, the micropore volume is 0.17 cm3 g−1 and micropore area is 384 m2 g−1, a micropore contribution of 55% of overall surface area. To the best of our knowledge, this one of the highest surface areas of a platinum coordination polymer.
Conclusions
Fig. 2 Depiction of the target honeycomb coordination network that would be obtained from reacting hexaaminotriptycene 5 with K2PtCl4. The structure of 6, which represents a fragment of the honeycomb lattice, is shown on the top left to indicate the dimensions of an edge.
16476 | Dalton Trans., 2013, 42, 16474–16477
In summary, we describe a new concept for constructing a porous honeycomb lattice based on triptycene, where metal coordination is used to link them into a hexagonal structure. We have made the first metal complex of o-triptycenesemiquinonediimine and verified its structure by many techniques, including a 15N labelling experiment. By replacing diaminotriptycene with hexaaminotriptycene, a porous, insoluble coordination polymer based on triptycene was formed. The lack of significant X-ray diffraction from the material suggests that the structure is disordered. Nonetheless, this new approach to linking triptycene groups using benzenesemiquinonediimine motifs is a promising way to assemble molecular hexagons and extended honeycomb structures, and we are continuing to pursue these goals.
This journal is © The Royal Society of Chemistry 2013
View Article Online
Dalton Transactions
Acknowledgements
Published on 16 October 2013. Downloaded by Universitat Politècnica de València on 25/10/2014 12:28:32.
We thank NSFC (21073235, 21177160) and NSERC for funding. NGW thanks the Killam Foundation for a Post-doctoral Fellowship.
Notes and references ‡ Crystal data for 6: Monoclinic, space group: P21/c, a = 11.8563(9) Å, b = 8.1225(5) Å, c = 23.6634(17) Å, α = γ = 90°, β = 93.544(3)°, V = 2274.5(3) Å3, Z = 2, T = 173 K, F(000) = 916, ρcalcd = 1.34 g cm−3, μ(Mo Kα) = 3.213 mm−1 (λ = 0.71073 Å), 41 855 measured reflections, 4676 independent reflections (Rint = 0.0316), 256 refined parameters, R1 = 0.0372 for I > 2σ(I), and wR2 = 0.0987, GOF = 1.084.
1 C. M. A. Parlett, K. Wilson and A. F. Lee, Chem. Soc. Rev., 2013, 42, 3876; D. Wu, F. Xu, B. Sun, R. Fu, H. He and K. Matyjaszewski, Chem. Rev., 2012, 112, 3959; J. Tian, P. K. Thallapally and B. P. McGrail, CrystEngComm, 2012, 14, 1909; D. Bradshaw, J. B. Claridge, E. J. Cussen, T. J. Prior and M. J. Rosseinsky, Acc. Chem. Res., 2005, 38, 273. 2 Recent activity: J. T. A. Jones, T. Hasell, X. Wu, J. Bacsa, K. E. Jelfs, M. Schmidtmann, S. Y. Chong, D. J. Adams, A. Trewin, F. Schiffman, F. Cora, B. Slater, A. Steiner, G. M. Day and A. I. Cooper, Nature, 2011, 474, 367; C. G. Bezzu, M. Helliwell, J. E. Warren, D. R. Allan and N. B. McKeown, Science, 2010, 327, 1627; Z. Xiang and D. Cao, J. Mater. Chem. A, 2013, 1, 2691; C. Tedesco, L. Erra, M. Brunelli, V. Cipolletti, C. Gaeta, A. N. Fitch, J. L. Atwood and P. Neri, Chem.–Eur. J., 2010, 16, 2371; J. Tian, S. Ma, P. K. Thallapally, D. Fowler, B. P. McGrail and J. L. Atwood, Chem. Commun., 2011, 47, 7626. 3 T. Tozawa, J. T. A. Jones, S. I. Swamy, S. Jiang, D. J. Adams, S. Shakespeare, R. Clowes, D. Bradshaw, T. Hasell, S. Y. Chong, C. Tang, S. Thompson, J. Parker, A. Trewin, J. Basca, A. M. Z. Slawin, A. Steiner and A. I. Cooper, Nat. Mater., 2009, 8, 973; G. Férey, Chem. Soc. Rev., 2008, 37, 191. 4 J. L. C. Rowsell and O. M. Yaghi, Microporous Mesoporous Mater., 2004, 73, 3; H. Deng, S. Grunder, K. E. Cordova, C. Valente, H. Furukawa, M. Hmadeh, F. Gándara, A. C. Whalley, Z. Liu, S. Asahina, H. Kazumori, M. O’Keeffe, O. Terasaki, J. F. Stoddart and O. M. Yaghi, Science, 2012, 336, 1018. 5 B. S. Ghanem, K. J. Msayib, N. B. McKeown, K. D. M. Harris, Z. Pan, P. M. Budd, A. Butler, J. Selbie, D. Book and A. Walton, Chem. Commun., 2007, 67; J.-S. Yang and T. M. Swager, J. Am. Chem. Soc., 1998, 120, 5321; T. M. Swager, Acc. Chem. Res., 2008, 41, 1181; C. Zhang, Y. Liu, B. Li, B. Tan, C.-F. Chen, H.-B. Xu and X.-L. Yang, ACS Macro Lett., 2012, 1, 190; N. T. Tsui, L. Torun, B. D. Pate, A. J. Paraskos, T. M. Swager and E. L. Thomas, Adv. Funct. Mater., 2007, 17, 1595.
This journal is © The Royal Society of Chemistry 2013
Communication 6 J. H. Chong, S. J. Ardakani, K. J. Smith and M. J. MacLachlan, Chem.–Eur. J., 2009, 15, 11824; M. Mastalerz, M. W. Schneider, I. M. Oppel and O. Presly, Angew. Chem., Int. Ed., 2011, 50, 1046. 7 J. H. Chong and M. J. MacLachlan, Inorg. Chem., 2006, 45, 1442; M. Munakata, L. P. Wu, K. Sugimoto, T. KurodaSowa, M. Maekawa, Y. Suenaga, N. Maeno and M. Fujita, Inorg. Chem., 1999, 38, 5674; X. Roy, J. H. Chong, B. O. Patrick and M. J. MacLachlan, Cryst. Growth Des., 2011, 11, 4551; S. Vagin, A. Ott, H.-C. Weiss, A. Karbach, D. Volkmer and B. Rieger, Eur. J. Inorg. Chem., 2008, 16, 2601; S. I. Vagin, A. K. Ott, S. D. Hoffmann, D. Lanzinger and B. Rieger, Chem.–Eur. J., 2009, 15, 5845; C.-H. Lee, R. Filler, J. Lee, J. Li and B. K. Mandal, Renewable Energy, 2010, 35, 1592; A. K. Crane, B. O. Patrick and M. J. MacLachlan, Dalton Trans., 2013, 42, 8026. 8 J. H. Chong and M. J. MacLachlan, Chem. Soc. Rev., 2009, 38, 3301; C.-F. Chen, Chem. Commun., 2011, 47, 1674. 9 M. Mastalerz and I. M. Oppel, Angew. Chem., Int. Ed., 2012, 51, 5252. 10 J. W. Colson, A. R. Woll, A. Mukherjee, M. P. Levendorf, E. L. Spitler, V. B. Shields, M. G. Spencer, J. Park and W. R. Dichtel, Science, 2011, 332, 228; C. J. Doonan, D. J. Tranchemontagne, T. G. Glover, J. R. Hunt and O. M. Yaghi, Nat. Chem., 2010, 2, 235; K. M. Ok, J. Sung, G. Hu, R. M. J. Jacobs and D. O’Hare, J. Am. Chem. Soc., 2008, 130, 3762; M. Lackinger, S. Griessl, W. M. Heckl, M. Hietschold and G. W. Flynn, Langmuir, 2005, 21, 4984. 11 B. S. Ghanem, M. Hashem, K. D. M. Harris, K. J. Msayib, M. Xu, P. M. Budd, N. Chaukura, D. Book, S. Tedds, A. Walton and N. B. McKeown, Macromolecules, 2010, 43, 5287. 12 C. Zonta, O. De Lucchi, A. Linden and M. Lutz, Molecules, 2010, 15, 226. 13 J. H. Chong and M. J. MacLachlan, J. Org. Chem., 2007, 72, 8683. 14 M. Mastalerz, S. Sieste, M. Cenić and I. M. Oppel, J. Org. Chem., 2011, 76, 6389. 15 P. Chaudhury, C. N. Verani, E. Bill, E. Bothe, T. Weyhermüller and K. Wieghardt, J. Am. Chem. Soc., 2001, 123, 2213. 16 D. Herebian, E. Bothe, F. Neese, T. Weyhermüller and K. Wieghardt, J. Am. Chem. Soc., 2003, 125, 9116. 17 Y. Konno and N. Matsushita, Bull. Chem. Soc. Jpn., 2006, 79, 1046; Y. Konno and N. Matsushita, Bull. Chem. Soc. Jpn., 2006, 79, 1237; T. Koizumi and K. Fukuju, J. Organomet. Chem., 2011, 696, 1232. 18 K. Chłopek, E. Bothe, F. Neese, T. Weyhermüller and K. Wieghardt, Inorg. Chem., 2006, 45, 6298; G. Ricciardi, A. Rosa, G. Morelli and F. Lelj, Polyhedron, 1991, 10, 955. 19 Sorption measurement of multiple samples gave surface areas in the range of ∼150–700 m2 g−1; the data presented are for one of the best samples.
Dalton Trans., 2013, 42, 16474–16477 | 16477
