Synthesis of Honeycomb Coordination Networks bySelf-assembly of the Tetradentate Ligand

1,2-bis(50-Dipyrimidyl)ethyne with Copper(I) Halides

Ivan Georgiev,a Charles L. Barnesb and Eric Boscha,*aDepartment of Chemistry, Southwest Missouri State University, Springfield, MO 65804, USA

bDepartment of Chemistry, University of Missouri, Columbia, MO 65211, USA

Received 23 April 2002; accepted 25 April 2002

Abstract—The structure of the honeycomb-like three-dimensional networks formed on self-assembly of the tetradentate ligand 1,2-bis(50-dipyrimidyl)ethyne with copper (I) iodide and copper (I) bromide are presented.# 2002 Elsevier Science Ltd. All rights reserved.

The design of nitrogen-based heterocyclic ligands forthe ordered and predictable self-assembly of super-structures through metal-ligand coordination currentlyattracts wide interest.1 The potential application of theresultant metallosuprastructures as useful electrical,magnetic and optical materials2 and as porous solids orzeolites,3 chemosensors4 and catalysts5 has been docu-mented. We recently presented the synthesis and coor-dination characteristics of a variety of pyridine andtriazine based ligands.6 In this communication, we dis-close our preliminary results directed toward the synth-esis of porous honeycomb materials based onpyrimidine ligands. In particular, we were intrigued bythe potential of the generic tetradentate bipyrimidylligands, 1, shown in Chart 1 to form a variety of coor-dination networks including the hexagonal networkshown in Chart 2. We reasoned that this approachmight provide a ‘tunable’ route to the controlled pre-paration of porous layered structures. Thus the lengthof the spacer unit in ligand 1 may be varied and may beeither rigid or flexible.

Ligand 2, that has a rigid linear ethynyl spacer, wasprepared in moderate yield by Sonogashira coupling7 of5-ethynylpyrimidine8 with 5-bromopyrimidine.9 Theligand was then allowed to self assemble with coppersalts by layering a dichloromethane solution of theligand with an acetonitrile solution of the copper salt.

After 2 days, orange crystals of the complex 3 began toform and the crystals were harvested after 5 days. Simi-lar reaction with copper(I) bromide yielded orangecrystals of the coordination product 4 after 3 days.

1472-7862/01/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.PI I : S1472-7862(02 )00007-2

Journal of Supramolecular Chemistry 1 (2001) 153–155

Chart 2.

Chart 1.

*Corresponding author. Tel.: +1-417-836-5506; fax: +1-417-836-5507; e-mail: erb625f@smsu.edu

The structures of both networks were determined andboth featured the hexagonal network shown in Chart2.10�12 Indeed, Figure 1A shows a slice through the struc-ture of the copper iodide coordination network 3. Thisis a two-dimensional sheet comprising tetracoordinatedligands that form hexagonal rings with eight copperatoms in each 30-atom ring. Adjacent copper atoms areconnected in the third dimension by pairs of bridgingiodide atoms to form infinite asymmetric copper iodideladders as shown in Figure 1C. The longer Cu–Cu dis-tance within the CuI ladders is 3.148A while the shorterCu–Cu contact, between adjacent ligands, is2.6675(13)A.13 The view along the b-axis in Figure 1Bshows the corrugated nature of the sheets and the axisof the copper iodide ladders. The offset packing ofadjacent two-dimensional sheets along with the angledcopper iodide ladders precludes formation of hexagonalcavities within the crystal lattice of 3. In contrast thecopper(I) bromide network 4 does form a hexagonalnetwork with a honeycomb-like structure. In this struc-ture each N is also coordinated to copper however theconnectivity within the network is different. The two-dimensional slice through the structure shown in Figure 2highlights the connectivity. Thus one, copper atom,Cu(I), bridges two ligands while the other two distinctcopper atoms are connected by a single bridging bromineatom to form a three-atom bridge between adjacent

ligands. One copper atom, Cu(3), has a coordinatedacetonitrile molecule. The distorted tetrahedral geo-metry about each copper is completed by bromineatoms that form infinite (CuBr) ribbons. Adjacentsheets overlay each other in such a way that hexagonalcavities are formed within the structure as shown inFigure 3. A second (uncoordinated) acetonitrile mole-cule is included within the hexagonal cavities.

We are currently exploring the self-assembly of net-works using other ligands based on design 1 with largerrigid spacers and with flexible spacers and a variety ofmetal cations.

References and notes

1. (a) Munakata, M.; Wu, L. P.; Kuroda-Sowa, T. Adv. Inorg.Chem. 1999, 46, 173. (b) Munakata, M.; Wu, L. P.; Kuroda-Sowa, T. Bull. Chem. Soc. Jpn. 1997, 70, 1727.

Figure 1. (A) Pluto view of one two-dimensional sheet of ligandsalong with the bound copper atoms with the iodine and hydrogenatoms omitted for clarity. (B) View along the b-axis of the stackedsheets showing the corrugated nature of the sheets and the axis of theconnecting copper iodide ladders. Iodine atoms omitted for clarity. (C)View of the infinite asymmetric copper iodide ladders with thermalellipsoids drawn at 30% probability.14

Figure 2. Pluto view of one sheet of the copper(I) bromide–2 networkshowing the coordinated acetonitrile. Hydrogen atoms omitted forclarity.

Figure 3. Stick drawing of the hexagonal channels formed in theCuBr–2 network 4 with both the coordinated and non-coordinatedacetonitrile molecules omitted for clarity.

154 I. Georgiev et al. / Journal of Supramolecular Chemistry 1 (2001) 153–155

2. (a) Miyasaka, H.; Matsumoto, N.; Okawa, H.; Re, N.;Gallo, B.; Floriani, C. J. Am. Chem. Soc. 1996, 118, 981. (b)Chen, C.-T.; Suslick, K. S. Coord. Chem. Rev. 1993, 128, 293.(c) McCleverty, J. A.; Ward, M. D. Acc. Chem. Res. 1998, 31,842.3. (a) Eddaoudi, M.; Moler, D. B.; Li, H.; Chen, B.; Reineke,T. M.; O’Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2001, 34,319. (b) Zaworotko, M. J. Angew. Chem., Int. Ed. 2000, 39,3052. (c) Lopez, S.; Keller, S. W. Inorg. Chem. 1999, 38, 1883.4. Kingsborough, R. P.; Swager, T. M. Prog. Inorg. Chem.1999, 48, 123.5. Fujita, M.; Kwon, J. K.; Washizu, S.; Ogura, K. J. Am.Chem. Soc. 1994, 116, 1151.6. (a) Bosch, E.; Barnes, C. L. Inorg. Chem. 2001, 40, 3097. (b)Bosch, E.; Barnes, C. L. Inorg. Chem. 2001, 40, 3234. (c)Bosch, E.; Barnes, C. L. New J. Chem. 2001, 25, 1376. (d)Bosch, E.; Barnes, C. L. Inorg. Chem. 2002, 41, 2543.7. Takahashi, S.; Kuroyama, Y.; Sonogashira, K.; Hagihara,N. Synthesis 1980, 627.8. 5-Ethynylpyrimidine was prepared from 5-bromopyr-imidine according to the general procedure described in ref 7.Characterization of 5-ethynylpyrimidine: 1H NMR � 9.18 (s,1H), 8.83 (s, 2H), 3.42 (s, 1H); 1H NMR � 159.30, 157.22,118.75, 84.43, 76.85. Anal. calc for C6H4N2: C, 69.22; H, 3.87;N, 26.91. Found C, 68.95; H, 3.85; N, 26.72.9. Characterization of 2: 1HNMR � 9.23 (s, 2H), 8.82 (s, 4H); 13CNMR � 158.83, 157.58, 118.59, 89.09. Anal. calc for C10H6N4: C,65.93; H, 3.32; N, 30.75. Found C, 65.66; H, 3.31; N, 30.48.10. X-ray structure determination: crystal data for 3:

C10H6Cu4I4N4, M=943.95, monoclinic, space group P2l/m,a=7.7025(7), b=15.7726(14), c=8.2876(8) A, b=114.3020(10)�,V=917.63(15) A3, T=173(2) K, Z=2. Dc=3.416 g cm�3, m(Mo-Ka)=11.298mm�1, F(000)=884. A crystal with dimensions0.35�0.25�0.20mm was measured on a Siemens SMART dif-fractometer. A total of 2840 reflections (2.58� <y <27.10�) werecollected of which 1041 were unique. The structure was solvedusing SHELXS-97 and refined using SHELXL-97 toR1=0.0363, wR2=0.0960 with I>2s(I) and R1=0.0387,wR2=0.0976 with all data.11. Crystal data for 4: C14H12Cu3Br3N6,M=694.65, monoclinic,space group P2l/c, a=9.5141(5), b=12.7091(7), c=16.5108(9) A,b=96.4570(10)�, V=1983.75(19) A3, T=173(2) K, Z=4,Dc=2.326g cm�3, m(Mo-Ka)=9.240mm�1, F(000)=1320. Acrystal with dimensions 0.40�0.25�0.25mm was measured on aSiemens SMART diffractometer. A total of 12,206 reflections(2.03� <y <27.12�) were collected of which 4364 were unique.The structure was solved using SHELXS-97 and refined usingSHELXL-9712 to R1=0.0305, wR2=0.0596 with I>2s(I)and R1=0.0505, wR2=0.0643 with all data.12. (a) Sheldrick, G. M. SHELXS-97, Crystal Structure Solu-tion; University of Gottingen: Germany, 1997. (b) Sheldrick,G. M. SHELXL-97, Crystal Structure Refinement; Universityof Gottingen: Germany, 1997.13. These values are well within the range of Cu–Cu contactsin a variety of halogenocuprate structures. See: Jagner, S.;Helgesson, G. Adv. Inorg. Chem. 1991, 37, 1.14. Drawn using Ortep3: Farrugia, L. J. J. Appl. Crystallogr.1997, 30, 565.

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