Supramolecular design of coordination complexes of silver(I) and cadmium(II) with chiral bidentate bridging ligands

Polyhedron 68 (2014) 40–45

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Supramolecular design of coordination complexes of silver(I) and cadmium(II) with chiral bidentate bridging ligands Qi-Long Zhang a,b, Bi-Xue Zhu a,⇑, Zhu Tao a, Shi-Xia Luo c, Leonard F. Lindoy d,⇑, Gang Wei e,⇑ a

Key Laboratory of Macrocyclic and Supramolecular Chemistry, Guizhou University, Guizhou 550025, China Department of Chemistry, Guiyang Medical College, Guiyang 550004, China c School of Chemistry and Materials Science, Guizhou Normal University, Guiyang 550001, China d School of Chemistry, F11, The University of Sydney, NSW 2006, Australia e CSIRO Materials Science and Engineering, P.O. Box 218, Lindfield, NSW 2070, Australia b

a r t i c l e

i n f o

Article history: Received 29 July 2013 Accepted 23 September 2013 Available online 15 October 2013 Keywords: Ligands Silver Cadmium X-ray structure Nanochannel

a b s t r a c t Two diastereopure ligands, N,N0 -bis(4-pyridyl)idene(1R,2R)- diaminocyclohexane (L1) and N,N0 -bis (3-pyridyl)idene(1R,2R)-diaminocyclohexane (L2), have been synthesized and characterized. The interaction of L1 with Ag(I) ions and L2 with Cd(II) ions has been investigated. The structure of {[Ag(L1)2] (CF3SO3)4H2O}n (1) exhibits a (4,4)-connected two-dimensional sheet with a corrugated surface and the complex [Cd(L2)2(NO3)(3H2O)]nNO32H2O (2) forms an infinite single helical chain with a pitch of 47.25 Å. When viewed from the top of the chain, the infinite helical chain forms the wall of a hexagonal nanochannel with an opening of 1.2  1.2 nm. Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction Over the past decades, metal–organic frameworks (MOFs) have emerged as an important new class of porous materials with the potential for making a significant impact in the fields of separation, gas storage, catalysis and chemical sensing [1–12]. The versatile pore features of MOFs, such as Lewis acidity, hydrophobicity, redox activity, basicity, chirality, which result from the precise arrangement of the transition metals and the organic functional groups, play a key role in the creation of unique nanosized reaction media. For instance, Pluth et al. have provided examples of pKa shifts in metal–organic frameworks, and exploited the pKa shifts to promote the acid catalyzed hydrolysis in basic solution [13]. Such strategies exhibited a simple but useful way to modify the acidity or basicity properties of the substrate by supramolecular inclusion, and paved the way for the application of MOFs in catalysis and biomimetics. Among of these MOFs materials, N-containing heterocyclic bidentate ligands for the construction of some unique porous materials have been designed and synthesized, and their potential applications have now been well documented. However, the use of chiral diamines, such as trans-1R,2R-diaminocyclohex-

⇑ Corresponding authors. Tel.: +86 851 3620903; fax: +86 851 3620906 (B.-X. Zhu). E-mail address: [email protected] (B.-X. Zhu). 0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.poly.2013.09.035

ane, for the synthesis of chiral Schiff base ligands derived from formacyl pyridine have not received much attention [14–16]. Here, we report the results of a series of MOFs involving the (1R,2R)-N,N0 -bis(4-pyridyl)idene diaminocyclohexane ligand (L1) with Ag(I) and the (1R,2R)-N,N0 -bis(3-pyridyl)idene-diaminocyclohexane ligand (L2) with Cd(II) (Scheme 1). 2. Experimental All reagents required for the syntheses were obtained commercially and were either used as supplied or purified by standard methods prior to use. Elemental (C, H, N) analyses were obtained with a Vario ELIII elemental analyzer. IR spectra were recorded using KBr pellets on a Bio-Rad FTIR spectrophotometer in the 400–4000 cm1 range. The synthesis of L1 and L2 was based on previous literature [17]. 2.1. Synthesis of {[Ag(L1)2](CF3SO3)4H2O}n (1) Ag(CF3SO3) 0.257 g (1 mmol) in ethanol (10 mL) was added dropwise with stirring to L1 (0.292 g, 1 mmol) in ethanol (10 mL) and stirring was continued at room temperature for 2 h. Then the reaction mixture was kept in a refrigerator overnight. A white amorphous solid separated out. The solid was collected by filtration, washed with a few drops of methanol and dried at room temperature to give 1 as a white solid in 43% yield. The solid was

41

Q.-L. Zhang et al. / Polyhedron 68 (2014) 40–45 Table 2 Selective bonds lengths (Å) and angles (°) for 1 and 2. *

*

*

N

N

*

N

N

N

N

1

N

N 2

1

L (1R,2R)

L (1R,2R)

2 i

Scheme 1. Chemical strutures of L1 and L2.

dissolved in excess ethanol at room temperature, and slow evaporation of this solution yielded colorless block-shaped single crystals that proved suitable for X-ray analysis. FTIR (KBr pellet, cm1): 3467(m), 3137(s), 2940(s), 2861(m), 1643(s), 1597(s), 1556(m), 1451(w), 1408(s), 1323(w), 1271(s), 1230(m), 1170(m), 1035(s), 936(m), 820(s), 649(s), 541(w), 458(w), 436(m). Anal. Calc. for C37H48AgF3N8O7S: C 48.63; H 5.29; N 12.26. Found: C, 48.70; H, 5.22; N, 12.32%.

N(1)–Ag(1) N(4)–Ag(1) N(5)–Ag(1) N(8)–Ag(1)ii N(8)–Ag(1)–N(4)iii N(8)–Ag(1)–N(5)iii N(4)–Ag(1)–N(5) N(8)–Ag(1)–N(1)iv N(4)–Ag(1)–N(1)iv N(5)–Ag(1)–N(1)iv

2.423 (4) 2.278 (4) 2.382 (4) 2.247 (3) 143.4 (1) 112.8 (2) 89.0 (1) 94.7 (1) 103.6 (1) 112.9 (2)

Cd(1)–O(3W) Cd(1)–N(1) Cd(1)–N(4)v Cd(1)–O(2W) Cd(1)–O(1W) Cd(1)–O(6) Cd(1)–O(5) N(4)–Cd(1)vi O(3W)–Cd(1)–N(1) O(3W)–Cd(1)–N(4)v N(1)–Cd(1)–N(4)v N(1)–Cd(1)–O(2)W

2.292 (4) 2.298 (4) 2.534 (6) 2.337 (4) 2.344 (4) 2.527 (6) 2.539 (7) 2.301 (5) 86.7 (2) 87.3 (1) 174.5 (1) 86.6 (2)

Symmetry codes: (i) x + 1/2, y, z + 1/2; (ii) x + 3/2, y, z  1/2; (iii) x + 3/2, y, z + 1/2; (iv) x + 1/2, y, z  1/2; (v) y + 1, x + y, z  1/6; (vi) x  y  1, x  1, z + 1/6.

2.2. Synthesis of {[CdL2(NO3)(3H2O)]NO32H2O}n (2) Cd(NO3)24H2O (308 mg, 1 mmol) in ethanol (10 mL) was added slowly to a stirred solution of L2 (292 mg, 1 mmol) in ethanol (10 mL) and stirring was continued at room temperature for 2 h. The initial white precipitate that formed was filtered off. The filtrate was allowed to evaporate slowly to yield colorless single crystals, one of which was removed from the solution and used directly for X-ray analysis. Yield: 35%. IR (KBr pellet, cm1): 3435(w), 3133(m), 2934(w), 1644(w), 1388(s), 1197(w), 1131(w), 982(w), 940(w), 820(w), 702(w), 646(w). Anal. Calc. for C18H30CdN6O11: C 34.93; H 4.89; N 13.58. Found: C, 34.85; H, 4.82; N, 13.65%. 2.3. X-ray data collection and structure determinations Single crystal X-ray diffraction studies of 1 and 2 were performed at room temperature on a Bruker Smart Apex single crystal diffractometer using the u–x scan method. The data were collected using graphite monochromated Mo Ka radiation (k = 0.71073 Å). Unit cell dimensions were obtained using least-

Table 1 Crystal data for compounds 1 and 2. Compound

1

2

Formula Formula weight Crystal system Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z qcalc (g/cm3) l (mm1) Reflections collected Independent reflections Goodness-of-fit R indices [I > 2r(I)]

C37H48AgF3N8O7S 913.76 orthorhombic P 212121 13.256 (1) 18.341 (2) 17.758 (2) 90.00 90.00 90.00 4317.5 (7) 4 1.406 0.582 36 587 497 1.049 R1 = 0.0463, wR2 = 0.1242 R1 = 0.0598, wR2 = 0.1317 0.864 and 0.642

C18H30CdN6O11 618.88 trigonal P 61 9.839 (5) 9.839 (5) 47.25 (2) 90.00 90.00 120.00 3962 (3) 6 1.556 0.891 35 472 325 1.171 R1 = 0.0364, wR2 = 0.0775 R1 = 0.0389, wR2 = 0.0784 0.335 and 0.666

R indices all data Largest difference in peak and hole (e Å3)

Fig. 1. (a) ORTEP representation of the symmetry expanded local structure for 1 showing 30% thermal ellipsoids. (b) The structure of the two-dimensional coordination layer with the corrugated surface viewed along the crystallographic a axis. (c) View of two-dimensional (4,4)-coordination layer in the structure of 1, showing the tetrahedral coordination mode around the silver ions. The hydrogen atoms, CF3SO3 anions and H2O molecules have been omitted for clarity. (d) Packing diagram of 1 viewed down the crystallographic b axis. Uncoordinated CF3SO3 counterions are located in the channels. The H2O molecules have been omitted for clarity. (e) Space-filling diagram of 1. These channels, viewed down the b axis, are filled by the uncoordinated CF3SO3 anions. H2O molecules have been omitted for clarity.

squares refinements, and multiscan absorption corrections were applied using the SADABS program. Two water molecules in the unit cell of complex 2 have been omitted by the SQUEEZE option of the

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(Fig. 1d and e). These channels are filled by the uncoordinated CF3SO3 anions and guest H2O molecules. The shortest Ag  Ag distance between adjacent layers is 9.182 Å. This result suggests that similar coordination complexes can be formed by L1 ligands and silvers ions, even when different counter anions are used [17]. However, if the 4-substituted pyridine moiety on L1 was replaced by a 3-substituted pyridine moiety (L2), we found that a onedimensional helical chain of L2 with Cd(II) can be formed (Fig. 2).

3.2. Crystal Structure of {[CdL2(NO3)(3H2O)]NO32H2O}n (2) Inorganic and organic nanochannels, such as nanotubes, have received considerable attention due to their potential applications in nanoelectronics, molecular devices and sensors, ion exchange and catalysis [19–22]. It is possible to construct nanotubular structures using metal–organic helices containing bidentate bridging ligands as the building blocks [23,24]. We surmise that the twisted binding sites of chiral rigid bidentate bridging ligands based on the N,N0 -1R,2R-bicyclohexyl unit will induce the formation of helical structures when linked by a linear metal-connecting point. In this work we report the metal–organic nanotubular structure of {[CdL2(NO3)(3H2O)]NO32H2O}n (2). Compound 2 crystallizes in the chiral space group P61, with one cadmium atom, one L2 ligand,

Fig. 1 (continued)

platon program. Both structures were solved by direct methods using the program SHELXS86 in the winGX package [18]. Crystallographic data are summarized in Table 1, whilst selected bond lengths and angles are given in Table 2. 3. Results and discussion 3.1. Crystal Structure of {[Ag(L1)2](CF3SO3)4H2O}n (1) The asymmetric unit of {[Ag(L1)2](CF3SO3)4H2O}n (1) consists of one silver atom and two L1 ligand molecules (Fig. 1a). In each ligand molecule (N,N0 -bis(4-pyridyl)idene-1R,2R-diaminocyclohexane), the inner imino N-atoms are oriented in different directions, with the nearly gauche N–C–C–N torsion angles equal to 59.71° and 63.99°, which makes them inert to metal ion coordination. As a result, only the peripheral pyridyls coordinate to the silver ions. Every silver ion has a distorted tetrahedral coordination environment, being bound to four nitrogen donors from the four adjacent molecules of L1, with Ag–N bond distances in the range 2.247(3)–2.423(4) Å, and bond angles around the neighboring atoms ranging from 89.0(1)° to 143.4(1)°. The Ag(I) centers are extended by L1 ligands along two directions (Fig. 1b), resulting in a (4,4)-connected two-dimensional layer with a corrugated surface, in which four L1 ligands bridge four adjacent Ag atoms to form a 60-membered metallocycle with two opposite Ag  Ag distances of 17.758 and 13.256 Å (Fig. 1c). Significantly, these two-dimensional layers stack in a parallel fashion, producing a one-dimensional channel when viewed down the crystallographic b axis

Fig. 2. (a) ORTEP representation of the asymmetric unit expanded local structure for 2 (30% thermal ellipsoids). (b) A part of the one-dimensional right-handed helical chain of 2 propagating along the crystallographic c axis. (c) Six successive Cd(NO3)(H2O)3 units form a hexagonal structure viewed down the c axis. (d) Righthanded 61 helical chain of 2 built from alternating Cd(NO3)(H2O)3 units and L2. (e) View of the single-strand helical chain of 2 that shows a chiral nanochannel with an opening of 1.2  1.2 nm along the [1 0 0] direction, free H2O and NO3 have been omitted.

Q.-L. Zhang et al. / Polyhedron 68 (2014) 40–45

43

Fig. 2 (continued)

one coordinated nitrate anion, three coordinated water molecules, one uncoordinated nitrate anion and two guest water molecules in the asymmetric unit. In the asymmetric unit of 2 (Fig. 2a), each Cd(II) atom is seven-coordinated to two nitrogen atoms that come from two different L2 ligands, one bidentate nitrate anion occupying two coordination sites, and three oxygen atoms from three different water molecules. The coordination environment around the cadmium centre can be described as a distorted pentagonal bipyramidal, with a Cd–N bond distance of 2.298(4) Å and Cd–O bond distances ranging from 2.296(6) to 2.534(6) Å. The N–Cd–N bond angle is 174.51(2)°, and the O–Cd–O bond angles range from 46.96(2)° to 83.39(9)°. Due to the reciprocal arrangement of the two C–Nimine bonds in the rigid R,R-1,2-bicyclohexyl moiety, the adjacent cadmium centers are connected to each other by the nitrogen donors (pyridyl) of the bridging bidentate L2 ligands to form an infinite right-handed helical chain with a pitch of 47.25 Å, with each period corresponding to six L2 ligands (Fig. 2b). When viewed along the crystallographic c axis, the six successive Cd(NO3)(H2O)3 units are bridged by the bidentate backbones of L2 to form a hexagonal structure (Fig. 2c). Of particular interest is the observation that with the infinite helical chain running along the crystallographic c axis (Fig. 2d), the hexagonal structures are packed in an overlapping fashion around the crystallographic 61 axis to generate a huge one-dimensional hexagonal nanotube with an opening of 1.2  1.2 nm (Fig. 2e). The individual one-dimensional right-handed helical chain is extended along two parallel directions. The one-dimensional right-handed helical chains are extended in parallel to give a corrugated layer along the crystallographic b axis, whilst the adjacent chains are linked mainly via O(W)–H  N hydrogen bonds between the adjacent chains and O(W)–H  O bridging hydrogen bonds involving guest water molecules (Fig. 3a). When viewed along the crystallographic c axis, these helical chains intertwine with each other to give a periodically ordered interlocking architecture (Fig. 3b). The hexagonal structures are stacked in a parallel and

Fig. 3. (a) View of the one-dimensional right-handed helical chain extending along the crystallographic b axis. The hydrogen bonds connecting adjacent chains are shown as dashed lines. (b) View of the chiral chains extending along the crystallographic b axis to form a periodically ordered interlocking architecture. (c) View of the one-dimensional right-handed helical chain extending along the crystallographic a axis. The hydrogen bonds connecting adjacent chains are shown as dashed lines. (d) View of the chiral chains in 2 extending along the crystallographic a axis to form a periodically ordered interlocking architecture. (e) View of how the chiral chains in 2 are extended in parallel to form the wave-like structure. (f) and (g) Schematic diagrams showing the open channels within the quasi threedimensional chiral framework of 2. The uncoordinated NO3 anions are located in the channels. H2O molecules are not shown.

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overlapping fashion to form interlocked channels, which are partly filled with uncoordinated NO3 anions and guest water molecules. Simultaneously, the one-dimensional right-handed helical chains are extended in parallel to give a corrugated layer along the crystallographic a axis to give two-dimensional chiral layers in the crystallographic ac plane. Other hydrogen bonding interactions are also present between the above layers (Fig. 3c). When viewed along the crystallographic c axis the structure shows a periodically ordered interlocking architecture (Fig. 3d); if this is taken into account, 2 can be considered as a quasi three-dimensional arrangement viewed from slightly off the b axis (Fig. 3e). The shortest Cd  Cd distance between adjacent chains is 9.375 Å. When viewed along the crystallographic c axis, the partly overlapping nanochannels lead to a quasi three-dimensional chiral framework with smaller open channels (Fig. 3f and g). The channel looks more cylindrical than hexagonal, with the inner diameter being about 0.5 nm and being filled with uncoordinated NO3 anions and guest water molecules. 4. Conclusions

Fig. 3 (continued)

In this paper we report that the interaction of the diastereopure bipyridyl ligands N,N0 -bis(4-pyridyl)idene(1R,2R)-diaminocyclohexane (L1) with Ag(I) and N,N0 -bis(3-pyridyl)idene(1R,2R)-diaminocyclohexane (L2) with Cd(II) ions provides a facile means of generating two types of coordination polymers. In particular, a self-assembly of periodically ordered interlocked homochiral nanochannels based on helical chains that are built from the chiral rigid bidentate L2 ligand and linear metal-connecting points was observed. This study demonstrates that the pyridyl-containing bidentate ligands L1 and L2 are capable of coordinating metal centers with both Npyridyl donors and generate novel coordination polymers. The relative orientation of the nitrogen donors on the pyridyl rings and different metal centers are the determining factors in the structural topology of the metal–organic supramolecular architectures [25–27]. Further studies using other metal centers for the construction of novel coordination-based networks and their properties such as enantioselective separation and catalysis are under way in our laboratory. Acknowledgments The support of the Natural Science Foundation of China (Grant No. 21061003), the International Cooperation Foundation of the Guizhou Province of PR China (Grant No. 700104), the Australian Research Council and the Australian partnership are gratefully acknowledged. Appendix A. Supporting information CCDC 872939 and 872938 contain the supplementary crystallographic data for 1 and 2. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223-336-033; or e-mail: [email protected]. Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/ 10.1016/j.poly.2013.04.062. References [1] [2] [3] [4]

Fig. 3 (continued)

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