Communication pubs.acs.org/Organometallics
Anisotropic Crystals Based on a Main-Group Coordination Polymer with Alignment of Rigid π Skeletons Masaichi Saito,*,† Tomoki Akiba,† Shunsuke Furukawa,† Mao Minoura,‡ Masahiko Hada,§ and Hiroshi Y. Yoshikawa† †
Department of Chemistry, Graduate School of Science and Engineering, Saitama University, Shimo-okubo, Sakura-ku, Saitama-city, Saitama 338-8570, Japan ‡ Department of Chemistry, School of Science, Rikkyo University, Nishi-ikebukuro, Toshima-ku, Tokyo 171-0021, Japan § Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Minami-Osawa, Hachi-Oji, Tokyo 192-0397, Japan S Supporting Information *
ABSTRACT: We succeeded in the alignment of π skeletons, resulting in the formation of anisotropic crystals. The combination of plumbacyclopentadienylidene, which has a divalent lead atom incorporated into the π skeleton, and 1,4dioxane afforded a coordination polymer, where the π skeletons are completely aligned in the same direction. The resulting plumbylene chains are also aligned in the same direction in the solid state, and therefore the crystals are noncentrosymmetric, showing second-harmonic generation (SHG) properties. Using pyrazine instead of 1,4-dioxane afforded an adduct composed of three plumbole units and two pyrazine molecules, and the crystals are symmetric and exhibit no SHG properties. The solid-state structures and optical properties are highly dependent on the Lewis base utilized. The present findings spotlight the use of group 14 divalent species incorporated into a π skeleton as a novel, useful method for the creation of a π-aligned coordination polymer with NLO properties. lignment of π-conjugated units is of fundamental importance and has long been receiving considerable attention in terms of structural chemistry, including nanostructures and materials engineering.1 In this field, much attention has recently been paid to coordination polymers, including metal−organic skeletons,2 composed of π-conjugated ligands and metal ions, which can construct a π−π stacking molecular architecture.3 Such metal ions functioning as coordinated atoms are commonly transition metals and lanthanides. On the other hand, p-block ions as coordinated atoms have still mainly been limited to group 1 and 2 metal ions,4,5 and quite recently, group 13 metal halides have received considerable attention as coordination centers.6 Coordination polymers based on pblock elements incorporated into π-conjugated skeletons would therefore be of considerable interest and potential use in terms of a new class of coordination polymers. To align π-conjugated units in a coordination polymer, we focused on a group 14 divalent atom conjugated in a π skeleton. We envisaged that a vacant p orbital in a divalent atom7 would be coordinated through its vacant p orbital by a Lewis base that has two coordinating sites to construct a coordination polymer with the alignment of the π skeletons. We chose a plumbacyclopentadienylidene, where a plumbylene unit is incorporated into a π skeleton.8 Another interesting feature of coordination polymers is their potential application as nonlinear optical (NLO) materials,9 which should have anisotropy without inversion
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symmetry in the solid state. However, such examples are limited to the combination of metal ions and electronically asymmetric ligands, whereas a coordination polymer with NLO properties constituted by an organometallic skeleton still remains less explored,10 even though NLO materials based on small organometallic compounds have been intensely studied.11 With this in mind, the plumbacyclopentadienylidene skeleton is expected to be a potential platform to induce anisotropy in the solid state by taking advantage of a vacant p orbital to regulate the direction of its π skeleton. We report herein a novel method for the alignment of a π skeleton: the use of a coordination polymer composed of a group 14 divalent species conjugated in a π skeleton and a Lewis base bearing two coordinating sites. The second harmonic generation (SHG) of the resulting polymer with anisotropic nature in the solid is also demonstrated. THF-coordinated plumbacyclopentadienylidene 18a was treated with 1,4-dioxane to suddenly afford a red precipitate of plumbylene chain 2, which is less soluble than 1 because of its polymeric structure (Scheme 1). Crystals suitable for X-ray Special Issue: Tailoring the Optoelectronic Properties of Organometallic Compounds with Main Group Elements Received: March 23, 2017
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DOI: 10.1021/acs.organomet.7b00217 Organometallics XXXX, XXX, XXX−XXX
Communication
Organometallics
composed of the two plumbole units and three dioxane molecules (Figure 1). Moreover, the dipole moment directions in the polymer chains are the same, producing a permanent dipole in the crystal (Figure 2). The formation of a polar crystal
Scheme 1. Preparation of Plumbylene Chain 2
diffraction analysis were obtained by recrystallization with slow diffusion (see the Supporting Information). The chain structure of 2 was fully established by X-ray diffraction analysis (see Table S1 in the Supporting Information). Two dioxane molecules perpendicularly coordinate a lead atom through its vacant 6p orbital from the top and the bottom, leading to a polymeric structure in the solid state (Figure 1). The space
Figure 2. Packing structure of plumbylene chain 2. All hydrogen atoms are omitted for clarity.
is considered to be generally unfavorable, resulting in an antiparallel arrangement of its dipole moment to minimize dipole−dipole interactions in the crystal. To consider the polarity of the crystal, quantum-chemical calculations based on density functional theory (DFT) were performed. As judged from the electrostatic potential map calculated at the B3LYP level of theory using the basis sets of aug-cc-pVTZ-pp13 for Pb and TZP14 for C in the plumbole rings and DZP15 for the other atoms, each of the dioxane molecules that are positively charged (depicted in blue) is situated between two negatively charged phenyl groups (depicted in red) of the neighboring plumbole rings in the next chain (Figure 3). This packing structure is considered preferable to other possible packing structures in terms of minimizing voids and steric repulsion (see Figure S1 in the Supporting Information). On the basis of the quantumchemical calculations and the consideration of steric effects, we can propose one possible reason for the crystal structure of compound 2: to maximize the electrostatic interaction, to
Figure 1. (a) ORTEP drawing of plumbylene chain 2, giving a side view of the plumbylene chain with thermal ellipsoid plots (50% probability). All hydrogen atoms and tert-butyl and two methyl groups on each of the silicon atoms are omitted for clarity. (b) Model compound for quantum-chemical calculations (for details, see the Supporting Information).
group of Fdd2 shows that the crystal is chiral with a Flack parameter of 0. The plumbole ring is almost planar with the sum of the internal bond angles being 539.5°. The C−C bond distances in the ring differ (1.349(3) and 1.517(4) Å), similarly to those found in 1, reflecting its nonaromatic character.8b The plumbylene unit is coordinated by two oxygen atoms of different dioxane molecules nearly perpendicularly to the plumbole ring, and the oxygen−lead−oxygen system is almost linear (172.9(2)°), as was observed in the structure of THF adduct 1 (175.62(6)°).8a The Pb−O distance of 2.5995(15) Å is slightly shorter than that of 1 (2.6635(19) Å). Notably, two oxygen atoms in a dioxane molecule coordinate lead atoms of the neighboring plumbole rings, leading to a coordination polymer structure in the solid state. It is noted that there are still only a few examples of coordination polymers with group 14 divalent species as the coordinated atoms.12 More interestingly, the plumbole rings in a polymer chain are completely aligned in the same direction with the distance between two lead atoms of about 8 Å, and a dipole moment is generated in a chain (Figure 1). The dipole moment is estimated to be 2.0 D by the calculation of a model structure
Figure 3. (a) Electrostatic potential surface of a part of the plumbylene chains composed of two plumbacyclopentadienylidenes and three dioxane molecules. (b) Polarity distribution in the plumbylene chains. All hydrogen atoms and tert-butyl and two methyl groups on each of the silicon atoms are omitted for clarity. B
DOI: 10.1021/acs.organomet.7b00217 Organometallics XXXX, XXX, XXX−XXX
Communication
Organometallics minimize steric repulsions and voids in the packing, all of the plumbole rings in the crystal face the same direction. As a result of the noncentrosymmetric orientation of plumbylene chains in the solid state, the crystal exhibits an anisotropic nature, which causes nonlinear optical properties. Due to its anisotropic nature in the solid state, the crystal of 2 reveals SHG-active properties. The process was studied for individual crystals using a femtosecond laser (λ 1000 nm), and the backward scattered light from the crystal was monitored. The spectrum of the light from the crystal exhibited a peak at 500 nm, clearly indicating that the SHG was detected (Figure 4). As the crystals degraded by air exposure did not reveal the
Figure 5. ORTEP drawing of pyrazine adduct 3. All hydrogen atoms and the tert-butyl and two methyl groups on each of the silicon atoms are omitted for clarity.
caused by the N2−Pb2−N2(#) angle of 167.24(11)°, which is similar to those of the bis(pyridine) adduct,8a and further coordination to afford a polymeric structure was suppressed. The lead atom of the central plumbole unit is coordinated by two nitrogen atoms with a distance of 2.706(3) Å, which is longer than the Pb1−N1 distance of 2.521(3) Å and those of the bis(pyridine) adduct (2.6877(17) Å).8a Consequently, one strong interaction or two weak interactions stabilize the plumbylene unit. The C−C distances in the plumbole rings in 3 are quite similar to those found in 2. The molecules are situated in an antiparallel fashion, and therefore the crystals have a symmetric structure, resulting in no anisotropic nature in the solid state of 3. A possible reason for this is discussed in Figure S2 in the Supporting Information. In summary, we have succeeded in the alignment of πconjugated skeletons by the use of a coordination polymer that is composed of group 14 divalent atoms incorporated into πconjugated skeletons with 1,4-dioxane molecules. The πconjugated skeletons are completely aligned in the same direction in each chain because of the electrostatic interactions between positively charged 1,4-dioxane molecules and negatively charged phenyl groups on the plumbole rings. The resulting chains are also aligned in the same direction, and the crystals therefore reveal anisotropy, which causes the SHG properties. In contrast, using pyrazine instead of 1,4-dioxane provided the pyrazine adduct bearing three plumbole units in the molecule, and the crystals are symmetric with no SHG properties, indicating that the choice of Lewis base is essential. The present findings exhibit a novel method for the creation of a a π-aligned coordination polymer with NLO properties.
Figure 4. Evaluation of SHG activity of the crystal of 2: (a) experimental setup for SHG measurements; (b) SHG spectrum; (c) SHG images (top, XY view; bottom, XZ view) of the crystal of 2.
SHG nature, the observed SHG is definitely caused by the anisotropy of the crystal. The single-crystal SHG efficiency was measured to be approximately 5% of that of urea. This SHG nature is worthy of note as the first example of anisotropy derived from a coordination polymer based on a π-conjugated organometallic skeleton. The small SHG efficiency is caused by the instability of compound 2 toward air and moisture. In contrast with the case for 1,4-dioxane, which afforded coordination polymer 2, using pyrazine produced pyrazine adduct 3 composed of three plumbole moieties and two pyrazine molecules (Scheme 2, Figure 5, and Table S1 in the Supporting Information). The molecular axis of Pb−N···N− Pb−N···N−Pb deviates from linearity and has a bow shape. The distinct difference in the structures between 2 and 3 is Scheme 2. Preparation of Pyrazine Adduct 3
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.7b00217. Details of the experiments and quantum-chemical calculations and NMR spectra of all new compounds (PDF) C
DOI: 10.1021/acs.organomet.7b00217 Organometallics XXXX, XXX, XXX−XXX
Communication
Organometallics Accession Codes
P.; West, R. In The Chemistry of Organic Silicon Compounds; Wiley: Chichester, U.K., 2003; pp 2463−2568. (d) Tokitoh, N.; Sasamori, T. In Comprehensive Inorganic Chemistry II, 2nd ed.; Poeppelmeier, K., Ed.; Elsevier: Amsterdam, 2013; pp 567−577. (8) (a) Saito, M.; Akiba, T.; Kaneko, M.; Kawamura, T.; Abe, M.; Hada, M.; Minoura, M. Chem. - Eur. J. 2013, 19, 16946−16953. (b) Kawamura, T.; Abe, M.; Saito, M.; Hada, M. J. Comput. Chem. 2014, 35, 847−853. (9) (a) Janiak, C.; Scharmann, T. G.; Albrecht, P.; Marlow, F.; Macdonald, R. J. Am. Chem. Soc. 1996, 118, 6307−6308. (b) Xiong, R.G.; Zuo, J.-L.; You, X.-Z.; Abrahams, B. F.; Bai, Z.-P.; Che, C.-M.; Fun, H.-K. Chem. Commun. 2000, 2061−2062. (c) Han, L.; Hong, M.; Wang, R.; Luo, J.; Lin, Z.; Yuan, D. Chem. Commun. 2003, 2580− 2581. (d) Wang, Y.-T.; Fan, H.-H.; Wang, H.-Z.; Chen, X.-M. Inorg. Chem. 2005, 44, 4148−4150. (10) Heine, J.; Hołyńska, M.; Reuter, M.; Haas, B.; Chatterjee, S.; Koch, M.; Gries, K. I.; Volz, K.; Dehnen, S. Cryst. Growth Des. 2013, 13, 1252−1259. (11) (a) Rosemann, N. W.; Eußner, J. P.; Dornsiepen, E.; Chatterjee, S.; Dehnen, S. J. Am. Chem. Soc. 2016, 138, 16224−16227. (b) Rosemann, N. W.; Eußner, J. P.; Beyer, A.; Koch, S. W.; Volz, K.; Dehnen, S.; Chatterjee, S. Science 2016, 352, 1301−1304. (12) (a) Rae, A. D.; Craig, D. C.; Dance, I. G.; Scudder, M. L.; Dean, P. A. W.; Kmetic, M. A.; Payne, N. C.; Vittal, J. J. Acta Crystallogr., Sect. B: Struct. Sci. 1997, 53, 457−465. (b) Appleton, S. E.; Briand, G. G.; Decken, A.; Smith, A. S. Dalton Trans. 2004, 3515−3520. (c) Dean, P. A. W.; Vittal, J. J.; Payne, N. C. Inorg. Chem. 1985, 24, 3594−3597. (13) Peterson, K. A.; Figgen, D.; Goll, E.; Stoll, H.; Dolg, M. J. Chem. Phys. 2003, 119, 11113−11123. (14) Barbieri, P. L.; Fantin, P. A.; Jorge, F. E. Mol. Phys. 2006, 104, 2945−2954. (15) Canal Neto, A.; Muniz, E. P.; Centoducatte, R.; Jorge, F. E. J. Mol. Struct.: THEOCHEM 2005, 718, 219−224.
CCDC 1509897−1509898 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
[email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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AUTHOR INFORMATION
Corresponding Author
*E-mail for M.S.:
[email protected]. ORCID
Masaichi Saito: 0000-0001-6176-3034 Shunsuke Furukawa: 0000-0001-7531-407X Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was partially supported by the Grants-in-Aid for Scientific Research on Innovative Areas “π-System Figuration, Control of Electron and Structural Dynamism for Innovative Functions” (No. 26102006 for M.S.) and “Stimuli-responsive Chemical Species for the Creation of Functional Molecules” (Nos. 15H00918 and 15H00962 for S.F. and M.M., respectively) and a Grant-in-Aid for Challenging Exploratory Research (16K13945 for S.F.) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan. The authors thank Professor Junichi Nakai at Saitama University for helping us investigate the SHG nature of the compounds. This article is dedicated to Professor Takayuki Kawashima on the occasion of his 70th birthday.
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REFERENCES
(1) (a) Kawase, T.; Kurata, H. Chem. Rev. 2006, 106, 5250−5273. (b) Wasielewski, M. R. Acc. Chem. Res. 2009, 42, 1910−1921. (c) Drain, C. M.; Varotto, A.; Radivojevic, I. Chem. Rev. 2009, 109, 1630−1658. (d) Klosterman, J. K.; Yamauchi, Y.; Fujita, M. Chem. Soc. Rev. 2009, 38, 1714−1725. (e) Martinez, C. R.; Iverson, B. L. Chem. Sci. 2012, 3, 2191−2201. (2) (a) Janiak, C. Dalton Trans. 2003, 2781−2804. (b) Kitagawa, S.; Kitaura, R.; Noro, S.-i. Angew. Chem., Int. Ed. 2004, 43, 2334−2375. (3) (a) Roesky, H. W.; Andruh, M. Coord. Chem. Rev. 2003, 236, 91− 119. (b) Ye, B.-H.; Tong, M.-L.; Chen, X.-M. Coord. Chem. Rev. 2005, 249, 545−565. (c) Ganguly, R.; Sreenivasulu, B.; Vittal, J. J. Coord. Chem. Rev. 2008, 252, 1027−1050. (4) Fromm, K. M. Coord. Chem. Rev. 2008, 252, 856−885. (5) (a) Guo, Z.; Li, G.; Zhou, L.; Su, S.; Lei, Y.; Dang, S.; Zhang, H. Inorg. Chem. 2009, 48, 8069−8071. (b) Kizzie, A. C.; Wong-Foy, A. G.; Matzger, A. J. Langmuir 2011, 27, 6368−6373. (c) Zhang, X.; Huang, Y.-Y.; Lin, Q.-P.; Zhang, J.; Yao, Y.-G. Dalton Trans. 2013, 42, 2294−2301. (6) (a) Yu, J.; Cui, Y.; Wu, C.; Yang, Y.; Wang, Z.; O’Keeffe, M.; Chen, B.; Qian, G. Angew. Chem., Int. Ed. 2012, 51, 10542−10545. (b) Sava, D. F.; Rohwer, L. E. S.; Rodriguez, M. A.; Nenoff, T. M. J. Am. Chem. Soc. 2012, 134, 3983−3986. (c) Cepeda, J.; Beobide, G.; Castillo, O.; Luque, A.; Pérez-Yáñez, S.; Román, P. Cryst. Growth Des. 2012, 12, 1501−1512. (d) Sevastianova, T. N.; Bodensteiner, M.; Maulieva, A. F.; Davydova, E. I.; Virovets, A. V.; Peresypkina, E. V.; Balazs, G.; Gra; Seidl, M.; Scheer, M.; Frenking, G.; Berezovskaya, E. A.; Kazakov, I. V.; Khoroshilova, O. V.; Timoshkin, A. Y. Dalton Trans. 2015, 44, 20648−20658. (e) Dhara, B.; Sappati, S.; Singh, S. K.; Kurungot, S.; Ghosh, P.; Ballav, N. Dalton Trans. 2016, 45, 6901− 6908. (7) (a) Neumann, W. P. Chem. Rev. 1991, 91, 311−334. (b) Tokitoh, N.; Okazaki, R. Coord. Chem. Rev. 2000, 210, 251−277. (c) Gaspar, P. D
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