Interpenetrating Metal-Organic Frameworks Assembled from Polypyridine Ligands and Cyanocuprate Catenations Can Liu, You-Bang Ding, Xu-Hua Shi, Dan Zhang, Mei-Hong Hu, Ye-Gao Yin,* and Dan Li*
CRYSTAL GROWTH & DESIGN 2009 VOL. 9, NO. 3 1275–1277
Department of Chemistry, Shantou UniVersity, Shantou, Guangdong-515063, PR China ReceiVed October 29, 2008; ReVised Manuscript ReceiVed January 28, 2009
ABSTRACT: Two three-dimensional coordination polymers, [(CuCN)3(4-pyBpy)]n (1) and [(CuCN)4(3-pyBpy)]n (2), as rare examples of coordination polymers of nonchelating quaterpyridines, demonstrating 4- and 2-fold interpenetrations, respectively, were isolated from solvothermal reactions of 2,6-bis(4-pyridyl)-4,4′-bipyridine (4-pyBpy) and 2,6-bis(3-pyridyl)-4,4′-biyridine (3-pyBpy) with CuCN in DMF and were structurally characterized. d10 M(I)-CN systems have attracted great attention in coordination chemistry for their unusual bond basics and pertinence to industrial uses, such as electroplating, metal abstraction, ceramic superconductor making, and so on.1,2 However, more recently, such binary combinations, especially, cuprocyanide catenations (CCCs), because the act as cocrystallizing counterparts and building blocks of metal-organic frameworks (MOFs) with dazzling configurations, have evoked new interest in crystal engineering.3,4 By CCC-based coordination polymers, assemblies are found that are subject to a third species as either a counterion5 or ligand incorporating with CCCs.6 As support to the conclusion, we illustrated previously the effects of a third species as a ligand on the assembly of CCC by 4′-(4-pyridyl)-2,2′:6′,2′′-terpyridine,7 and as counterions by two M(II)-terpyridine complexes.8 To carry forward the design based on polypyridines, we treated solvothermally two isomeric nonchelating quaterpyridines, namely, 4- and 3-pyBpy (Scheme 1), in parallel, with CuCN, with the aim to show the effect of the chemically homogeneous, but geometrically different, ligands on the constructions of CCCs. This led to two new coordination polymers, [(CuCN)3(4-pyBpy)]n (1) and [(CuCN)4(3-pyBpy)]n (2), noteworthy giving the first two 3D coordination polymers of the ligands and showing diverse network interpenetrations, an aspect of interest to structural crystal engineering.9 Isolation of 1, as orange air-stable crystals, was achieved by solvothermal reaction of 4-pyBpy with CuCN in DMF.10 It was characterized by X-ray diffraction a 3D MOF, solidifying in a centrosymmetric orthogonal Pbcn space group (No. 60) (Figure 1a) and consisting of Cu(I), CN-, and 4-pyBpy elements.11 In the ternary edifice, the Cu(I) ions are similarly three-coordinated, but crystallographically they are sorted into two classes, of which the Cu1, with a site occupation factor (SOF) of 1/2, bonds to a N3 of 4-pyBpy (Cu1-N3 2.127(3) Å) and two CN-’s, while the Cu2, with a SOF of 1, binds to a N1 of 4-pyBpy (Cu2-N1 2.047(3) Å) and two CN-’s. In contrast, the 4-pyBpys in 1 are uniform, each exhibiting a C2 symmetry about axis coincident with the Cu1-N3 bond (see Figure S1, Supporting Information) and functioning as trifurcated linkers, furnishing a Cu3 isosceles triangle (Cu2-Cu1-Cu2 56.14°, Cu1-Cu2-Cu2 61.93°; Cu1-Cu2 13.61(2) Å, Cu2-Cu2 12.81(2) Å). In geometry, the trifoliate 4-pyBpy is similar to 2,4,6tris-(4-pyridyl)-1,3,5-triazine, and hence, its combination to CuCN gave an allomeric network of the triazine-CCC,12 featured with the 24-, 30-, and 42-membered coordination loops ((Figure S2, Supporting Information) and (Figure S3, Supporting Information) and giving a 6(2).10 topology, in denoting the ligand and Cu(I) as three-connected nodes. More than that, the framework of 1, like the * To whom correspondence should be addressed. E-mail:
[email protected]. Tel. 86-0754-82903699. Fax: 86-0754-82902828.
Scheme 1. The Structures of Quaterpyridine Ligands
reference, is porous, allowing a [2 + 2]-type 4-fold interpenetration (Figure 1b). The allomery of 1 to the cited MOF proves the conclusion that the geometry of the ligand plays a dominating role in the formation of CCCs. On the other hand, it is also noticed that, owing to the difference in atomic content of 4-pyBpy compared to triazine, some structural characteristics of 1, such as the ligand-spaced Cu-Cu distances and the period of the sinuous 1D CCCs (Figure S4, Supporting Information), are still different from those cited.12
Figure 1. (a) The perspective views of 1 along a (left) and b (right) (Cu red, C black, and N blue) and (b) the [2 + 2] interpenetration of 6(2).10 networks of 1.
10.1021/cg801217j CCC: $40.75 2009 American Chemical Society Published on Web 02/16/2009
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Figure 2. (a) A perspective view of 2 along a and (b) the drawing of a separated 2D CCC sheet in 2 and (c) the topologic presentation of two interpenetrating networks of 2.
As we know, the 4-pyBpy has only been crystallographically documented as ligands of 1D and 2D Co(II) coordination polymers,13 and so 1 is the first 3D coordination polymer of 4-pyBpy. The lack of such a case is likely due to the bulkiness and multimonodentation of 4-pyBpy because these characteristics relate to the lability of a complex, which has been confirmed by the failures in isolating 3D MOFs by reactions of the ligand with CuCl and CuBr. On this basis, we assume the cyanide acts as a spacing linker lowering the intramolecular tension and so enabling the formation of 1. To show further the effect of ligand geometry on the assembly of CCCs, we used 3-pyBpy, an isomer of 4-pyBpy, which has only been reported as a counterion of calix-4-arene tetrasulphoate,14 as a ligand in the place of 4-pyBpy to react with CuCN. Finally, a new coordination polymer 2, as depicted in Figure 2a, unlike 1, containing 2D CCC sheets as a component, was afforded. For the homogeneity with 4-pyBpy, 3-pyBpy in 2 functions also as a tritopic linker, each furnishing a Cu3 triangle (Figure S5, Supporting Information) with Cu-N bonds ranging from 2.010(1)-2.144(1) Å very comparable with those of 1. However, its fork-like symmetry led to the discrimination of Cu(I) atoms into four classes and cyanides into µ2 and µ3 modes, symbolized by the IR signals at 2121 and 2074 cm-1.15 And further the more diverse classification of Cu(I) and CN- ions resulted in the configuration of CCCs as tortuous sheets extending in the (0, 1/2, 1/2) plane (Figure 2b) and a long-termed 3(2).4(2).5.6.10(3).11 topology of 2. Illustratively, the network of 2 is also open, allowing a lower 2-fold interpenetration (Figure 2c), in which the networks are related each other by a translation of (0, 1, 0) (11.520(7) Å). This reveals, from another angle, a chemical kindred relation of two ligands and, in the mean time, a geometric discrepancy between them. 1 and 2 were comparably prepared from 4- and 3-pyBpy, so that the conformational diversity of CCCs in 1 and 2 can be ascribed to the influence of the ligand geometries. The proposal is meaningful to crystal engineering, proposing a way to modify the conformation of a CCC, as part of a MOF, and further to change the CCC-based property of a solid by altering the geometries of ligands. For
example, use of 3-pyBpy as a ligand leads to the 2D CCCs of 2, giving a Cu1-Cu1 distance of 2.564 Å, which is much shorter than the van der Waals radii sum of two Cu(I) atoms (2.8 Å), and so promising a Cu-Cu bonding-based photoemission of 2.16 Thermogravimetry revealed that 1 and 2 are both stable to heat at least up to 340 °C because of the high thermostability of ligands. The finding implicates the feasibility to fabricate a thermally stable MOF by using heavy ligands such as pyBpy’s. The solids of 1 and 2, when heated in a N2 atmosphere, similarly exhibit two major weight reductions in the range of room temperature to 700 °C and (Figure S6, Supporting Information). By the weight losses measured, the slope for 1 within 350-465 °C (53%) can be assigned to the loss of 4-pyBpy (calcd. 53.6%) and the one within 465-700 °C (ca. 17%) to CN- (calcd. 19%).17 And, based on the comparability of 2 in composition with 1, the signals of 2 can be accordingly assigned. In summary, the parallel solvothermal reactions of 3- and 4-pyBpy with CuCN generated two new coordination polymers, of interest in (1) representing the first two 3D coordination polymers of the nonchelating quaterpyridines and (2) showing interpenetrations of open quaterpyridine-CCC MOFs. Besides, the diverse configurations of CCCs in two products verify the effects of geometrically different ligands, as third species, on the assembly of CCCs and meanwhile suggest a way to control the functionalities of CCC-based solids by altering the geometry of ligands. Supporting Information Available: Crystallographic information files (CIF), thermogravimetric plots of 1 and 2, and some supplementary drawings beneficial for discussion. This information is available free of charge via the Internet at http://pubs.acs.org.
References (1) Lancashire, R. J. ComprehensiVe Coordination Chemistry; Wilkinson, G., Ed.; Pergamon: Oxford, 1987. (2) (a) Khan, N. A.; Baber, N.; Iqbal, M. Z.; Mazhar, M. Chem. Mater. 1993, 5, 1283. (b) Ondono-Castillo, S.; Fuertes, A.; Perez, F.; GomezRomero, P.; Casan-Pastor, N. Chem. Mater. 1995, 7 (4), 771.
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(11)
(12) (13) (14) (15)
(16) (17)
4-pyBpy. It was isolated as orange plate-like crystals in a yield of ca. 45%. Anal. Calcd for C40H28N8Cu7C7N7: C 45.12; H 2.24; N 16.80. Found: C 45.09; H 2.28; N 16.84. IR (KBr, cm-1): 2926w, 2121s, 2074w, 1600s, 1534m, 1473w, 1387s, 813m. Data collection: Diffraction data were collected at 293(2) K with a Bruker-AXS SMART CCD area detector diffractometer using a Mo KR radiation (λ ) 0.71073 Å) and ω scan with a width of 0.3°. Multiscan absorptions were applied. The structures of 1 and 2 were solved by the direct methods and refined by full-matrix least-squares refinement on F2. All hydrogen atoms were included in calculated positions and reined with isotropic thermal parameters riding on those of the parent atoms and all non-hydrogen atoms were refined with anisotropic thermal parameters. Structure solutions and refinements were performed with the SHELXL-97 package. For all the compounds, the bridging cyanides indicate the disorders with respect to C and N termini and these disorders are treated by adopting 50% possibility of C and N occupancies at those sites. More details see the CIF files, Supporting Information. Li, M.-X.; Miao, Zh.-X.; Shao, M.; Liang, Sh.-W.; Zhu, Sh.-R. Inorg. Chem. 2008, 47, 4481. Yoshida, J.; Nishikiori, S.; Kuroda, R. Chem. Lett. 2007, 36 (5), 678. Smith, C. B.; Makha, M.; Raston, C. L.; Sobolev, A. N. New J. Chem. 2007, 31, 535. (a) Nakamoto, K. Infrared and Roman Spectra of Inorganic Coordination Compounds, 4th ed.; Wiley: New York, 1986; p 272. (b) He, X.; Lu, C.-Z.; Yuan, D.-Q.; Chen, S.-M.; Chen, J.-T. Eur. J. Inorg. Chem. 2005, 11, 2181. Ford, P. C.; Cariati, E.; Bourassa, J. Chem. ReV. 1999, 99, 3625. Zhou, X.-P.; Li, D.; Wu, T.; Zhang, X.-J. Dalton Trans. 2006, 1.
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