Suprachannels via a Molecular Array of 2D Networks: Solvent Effects

Feb 27, 2014 - •S Supporting Information. ABSTRACT: The solvent effects on suprachannel formation via a molecular array of 2D networks were studied...
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Suprachannels via a Molecular Array of 2D Networks: Solvent Effects, Anion Exchange, and Physicochemical Properties of Silver(I) Complexes Bearing N,N′,N″‑Tris(2-pyridinylethyl)-1,3,5benzenetricarboxamide Euni Kim, Haeri Lee, Tae Hwan Noh, and Ok-Sang Jung* Department of Chemistry, Pusan National University, Pusan 609-735, Korea S Supporting Information *

ABSTRACT: The solvent effects on suprachannel formation via a molecular array of 2D networks were studied. The basic structure of the [Ag3L2](X)3 (X− = NO2−, NO3−) 2D network consists of hexagonal (Ag6L6) motifs formed via self-assembly of Ag(I) with C3-tridentate N-donors. The 2D networks are arranged in an eclipsed mode in aqueous solution, thus forming suprachannels (5.2 × 7.3 Å2, 6.2 × 7.7 Å2) of [Ag3L2(H2O)2](X)3, whereas they are arranged in a staggered abab... mode in nonaqueous solution, thus forming semisuprachannels (3.1 × 5.1 Å2) of [Ag3(NO3)2L2](NO3). The suprachannel structure of [Ag3L2(H2O)2](NO3)3 is soluble in methanol; contrastingly, the semisuprachannel structure of [Ag3(NO3)2L2](NO3) is insoluble in that solvent. In the present study, significant differences in molecular recognition and anion exchangeability between [Ag3L2(H2O)2](NO3)3 and [Ag3(NO3)2L2](NO3) were found.

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INTRODUCTION Molecular arrays of basic structures have inspired molecular chemists for the past decade owing to their utility for generating additional interesting physicochemical properties.1−7 Manipulation of novel molecular arrays is a hot topic and, not coincidentally, a great challenge in the field of molecular materials.6−10 Synthesis and array of functional coordination polymers with attractive motifs is a particularly significant endeavor, owing to their task-specific applications to molecular separation, toxic materials adsorption, molecular containers, ion exchangers, molecular recognition, and luminescent chemosensors.11−17 Functional coordination frameworks have been constructed by reaction of silver(I) ions with certain designed spacer ligands.15−19 The N-donor spacer ligands’ molecular geometry, length, and flexibility play key roles in the development of desirable coordination topologies. Porous coordination materials as site-selective hosts have proved good prototypes for generation of useful functions such as adsorption, gas storage, molecular recognition, anion exchange, and organic reaction catalysis.19−26 Indeed, the channel system’s modularity via component interchangeability has inspired numerous studies.27−32 In this context, various counteranion effects on molecular channel construction have been reported,18,33−38 though the detailed solvent effects on the formation of suprachannel structures via molecular arrays of well-ordered networks remain unexplored. In the present study, in an investigation of the solvent effects on suprachannel © 2014 American Chemical Society

formation via a molecular array, slow diffusion reactions of AgX (X− = NO2−, NO3−) with N,N′,N″-tris(2-pyridinylethyl)-1,3,5benzenetricarboxamide (L), as a key triangle-inducing tectonic, were carried out and scrutinized. We report herein those suprachannel structures’ crystal structures, photoluminescence, recognition, and anion exchange. The basic skeleton is a twodimensional (2D) network with two slightly different hexagons occupied by alcohol molecules and anions. The silver(I) ion utilized therein has been employed in various directional units such as linear, T-shaped, and tetrahedral geometries.39

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EXPERIMENTAL SECTION

Materials and Measurements. All chemicals including silver(I) nitrite (AgNO2) and silver(I) nitrate (AgNO3) were purchased from Aldrich and used without further purification. N,N′,N″-Tris(2pyridinylethyl)-1,3,5-benzenetricarboxamide (L) was prepared according to the procedure available in the literature.18 Elemental microanalyses (C, H, N) were performed on crystalline samples by using a Vario-EL analyzer at the Pusan Center, Korea Basic Science Institute (KBSI). Thermal analyses were carried out under a dinitrogen atmosphere at a scan rate of 10 °C/min using a Labsys TG-DSC 1600. Infrared spectra were obtained on a Nicolet 380 FT-IR spectrophotometer with samples prepared as KBr pellets. 1H (300 MHz) NMR spectra were recorded on a Varian Mercury Plus 300. Received: January 7, 2014 Revised: February 17, 2014 Published: February 27, 2014 1888

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Table 1. Crystal Refinement Parameters for [Ag3L2(H2O)2](NO2)3·10H2O, [Ag3L2(H2O)2](NO3)3·4CH3OH·4H2O, and [Ag3(NO3)2L2](NO3)·C2H5OH·3H2O formula Mw CCDC No. cryst syst space group a (Å) b (Å) c (Å) β (deg) V (Å3) Z ρ (g cm−3) μ (mm−1) Rint GOF on F2 R1 [I > 2σ(I)]a wR2 (all data)b a

[Ag3L2(H2O)2](NO2)3·10H2O

[Ag3L2(H2O)2](NO3)3·4CH3OH·4H2O

[Ag3(NO3)2L2](NO3)·C2H5OH·3H2O

C60H84N15O24 Ag3 1723.03 976463 monoclinic C2/c 32.438(1) 16.1532(4) 14.8332(8) 107.194(3) 7425.0(5) 4 1.541 0.867 0.0868 1.282 0.1016 0.3152

C64H88N15O25 Ag3 1791.10 976464 monoclinic C2/c 33.1540(5) 16.0516(2) 14.9568(2) 108.308(1) 7556.7(2) 4 1.574 0.856 0.0230 1.031 0.0747 0.2410

C62H72N15O19Ag3 1654.96 976465 monoclinic P21/c 14.1583(2) 27.6117(3) 9.6431(1) 94.526(1) 3758.07(8) 2 1.463 0.849 0.0431 1.028 0.0811 0.2846

R1 = ∑||Fo| − |Fc||/∑|Fo|. bwR2 = (∑[w(Fo2 − Fc2)2]/∑[w(Fo2)2])1/2. 4.00; N, 13.30. The anion exchanges were performed also in a mixed water and methanol solution (1:1, v/v). Crystal Structure Determination. X-ray data were collected on a Bruker SMART automatic diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) and a charge-coupled device (CCD) detector at ambient temperature. Thirty-six frames of twodimensional diffraction images were collected and processed to obtain the cell parameters and orientation matrix. The data were corrected for Lorentz and polarization effects. The absorption effects were corrected using the multiscan method (SADABS).40 The structures were resolved using the direct method (SHELXS 97) and refined by fullmatrix least-squares techniques (SHELXL 97).41 The non-hydrogen atoms were refined anisotropically, and the hydrogen atoms were placed in calculated positions and refined only for the isotropic thermal factors. The crystal parameters and procedural information corresponding to the data collection and structure refinement are listed in Table 1.

The absorption spectra were recorded on an S-3150 UV−vis spectrophotometer. Scanning electron microscopy (SEM) images were obtained on a Tescan VEGA 3. Powder X-ray diffraction (XRD) data were recorded on a Rigaku RINT/DMAX-2500 diffractometer at 40 kV and 126 mA for Cu Kα. Photoluminescence (PL) spectra were acquired on a FluoroMate FS-2 spectrofluorometer. Preparation of [Ag3L2(H2O)2](NO2)3·10H2O. A methanol solution (5 mL) of L (20.9 mg, 0.04 mmol) was slowly diffused into an aqueous solution (5 mL) of AgNO2 (9.2 mg, 0.06 mmol). Colorless crystals of [Ag3L2(H2O)2](NO2)3·10H2O, formed at the interface, were obtained in 5 days in 72% yield. Mp: 215 °C dec. Anal. Calcd for C60H84N15O24Ag3: C, 41.82; H, 4.91; N, 12.19. Found: C, 41.50; H,4.82; N, 12.10. IR (KBr, cm−1): 3299 (br), 3049 (w), 2938 (w), 1653 (s), 1596 (m), 1533 (s), 1476 (m), 1437 (m), 1274 (s, NO2−), 770 (w). Preparation of [Ag3L2(H2O)2](NO3)3·4CH3OH·4H2O. This complex was prepared in the same manner as [Ag3L2(H2O)2](NO2)3· 10H2O, except that AgNO3 was employed instead of AgNO2. Mp: 233 °C dec. Anal. Calcd for C64H88N15O25Ag3: C, 41.82; H, 4.91; N, 12.19. Found: C, 41.50; H, 4.80; N, 12.20. IR (KBr, cm−1): 3366 (br), 3068 (w), 2937 (w), 1655 (s), 1592 (m), 1542 (s), 1475 (m), 1436 (m), 1383 (s, NO3−), 770 (w). Preparation of [Ag3(NO3)2L2](NO3)·C2H5OH·3H2O. An ethanol solution (3 mL) of AgNO3 (5.1 mg, 0.03 mmol) was slowly diffused into a dichloromethane solution (3 mL) of L (10.4 mg, 0.02 mmol). Colorless crystals of [Ag3(NO3)2L2](NO3)·C2H5OH·3H2O, formed at the interface, were obtained in 5 days in 64% yield. Mp: 233 °C dec. Anal. Calcd for C62H72N15O19Ag3: C, 45.00; H, 4.39; N, 12.70. Found: C, 44.90; H, 4.42; N, 12.78. IR (KBr, cm−1): 3308 (br), 3058 (w), 2938 (w), 1653 (s), 1600 (m), 1543 (s), 1481 (m), 1438 (m), 1385 (s, NO3−), 770 (w). Anion Exchange. The anion exchange proceeded typically, as follows: an aqueous solution or a mixture of water and methanol (3 mL) of NaNO3 (38.3 mg, 0.45 mmol) was added to a suspension of microcrystalline [Ag3L2(H2O)2](NO2)3·10H2O (86.2 mg, 0.05 mmol) in water or a mixture of water and methanol (5 mL) at room temperature. The reaction mixture was stirred and then monitored by reference to the IR spectra. The counteranion exchange of [Ag3L2(H2O)2](NO3)3·4CH3OH·4H2O with NO2− was similarly achieved. After 12 h, the reaction mixture was filtered and washed with several aliquots of water and methanol. Anal. Calcd for C60H63N15O14Ag3: C, 46.71; H, 4.18; N, 13.62. Found for [Ag3L2(H2O)2](NO2)3 prepared by anion exchange: C, 46.40; H,

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RESULTS AND DISCUSSION Synthetic Aspects. Our strategy for construction and array of the molecular networks is outlined in Scheme 1. The basic structure of [Ag3(L)2](X) (X− = NO2−, NO3−) is a 2D grid of a nanosized hexagonal (Ag6L6) network formed via self-assembly of the tridentate N-donor tectonic (L) and a variety of coordination geometries of silver(I) ions. This self-assembly significantly depends on the solvents. That is, the self-assembly of AgNO3 in ethanol with L in dichloromethane in a 3:2 stoichiometry afforded colorless crystals of [Ag3(NO3)2L2](NO3)·C2H5OH·3H2O, whereas the similar reaction in a mixture of water and methanol produced [Ag3L2(H2O)2](NO3)3·4CH3OH·4H2O. Meanwhile, the self-assembly of AgNO2 in water with L in methanol, in a 3:2 stoichiometry produced colorless crystals of [Ag3L2(H2O)2](NO2)3·10H2O in high yields. However, a similar reaction of AgNO2 with L in a mixture of ethanol and dichloromethane did not yield single crystals suitable for X-ray crystallography. In all cases, the products’ formation was affected by the media, but was not significantly influenced by the change of the mole ratio or concentration. That is, self-assembly in the presence of aqueous media produces the suprachannel structure via an eclipsed molecular array of 2D grids, whereas similar treatment in nonaqueous media results in the semisuprachannel structure via 1889

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silver(0) particles. Its morphology and composition were confirmed by the powder XRD results (Supporting Information). Crystal Structures. The crystal structures are shown in Figures 1 and 2 and Figure S4 (Supporting Information), and

Scheme 1. Schematic Diagram for the Present Complexes (X− = NO2−, NO3−)

a staggered abab... array of 2D networks, which will be explained in detail. Thus, it can be established that the molecular array formed accords closely with the solvents employed in self-assembly. This result, furthermore, is a good example of the competition between water molecules and nitrate or nitrite anions to coordinate with silver(I) ions. The crystalline solids suitable for X-ray single crystallography were slowly decomposed in air, owing presumably to evaporation of the solvate molecules. In particular, the suprachannel coordination polymer [Ag3L2(H2O)2](NO3)3·4CH3OH·4H2O is soluble in methanol, whereas the semisuprachannel polymer [Ag3(NO3)2L2](NO3)·C2H5OH·3H2O is insoluble. Soluble silver(I) coordination polymers without skeletal dissociation are very unusual. Even discrete cyclodimeric silver(I) complexes are insoluble in common organic solvents. Common silver(I) coordination polymers are dissociated in strong polar solvents such as dimethyl sulfoxide and N,N-dimethylformamide.35 Of course, the original [Ag3L2(H2O)2](NO3)3· 4CH3OH·4H2O crystals could easily be obtained from the solution in the present case. The silver−ligand coordinated species in solution was investigated via FAB mass spectrometry (Figure S1 in the Supporting Information). The data (matrix 3nitrobenzyl alcohol) showed mass peaks corresponding to the mixtures of [Ag(L)]+ (629.9, calcd 629), [Ag(L)2]+ (1152.1, calcd 1151), and [Ag2(L)2(NO3)]+ (1321.5, calcd 1320) together with [L + H+]+ (524.0, calcd 523), indicating that the oligomeric structure of [Ag3L2(H2O)2](NO3)3·4CH3OH· 4H2O is maintained in solution. The 1H NMR spectrum of the soluble species is also provided in Figure S2 in the Supporting Information. All of the products were dissociated in dimethyl sulfoxide. For [Ag3L2(H2O)2](NO3)3·4CH3OH·4H2O and [Ag3(NO3)2L2](NO3)·C2H5OH·3H2O, the solvate molecules were evaporated at around 80 °C. Their skeletons started to decompose at around 230 °C with two-step procedures. Finally, above 400 °C, the thermally decomposed residue consisted of

Figure 1. Packing diagrams showing 1D channels for (a) [Ag 3 L 2 (H 2 O) 2 ](NO 2 ) 3 ·10H 2 O, (b) [Ag 3 L 2 (H 2 O) 2 ](NO 3 ) 3 · 4CH3OH·4H2O, and (c) [Ag3(NO3)2L2](NO3)·C2H5OH·3H2O. Inset: space-filling diagrams showing dimensions of suprachannels and semisuprachannels (suprachannel dimensions 5.2 × 7.3, 6.2 × 7.7, and 3.1 × 5.1 Å2, respectively).

their relevant bond lengths and angles are listed in Table 2. As is apparent, [Ag3L2(H2O)2](NO2)3·10H2O has both fourcoordinated and two-coordinated silver(I) ions (Supporting Information). The four-coordinated silver(I) ion was coordinated with two pyridyl moieties from two ligands (Ag−N = 2.203(5) Å, 2.206(6) Å; N−Ag−N = 156.0(2)°), one oxygen donor from the carbonyl moiety of L (Ag−O = 2.573(5) Å), and the other oxygen donor from the water molecule (Ag−O = 1890

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2.571(9) Å). The two-coordinated silver(I) ion is disordered (half-occupancy) and is coordinated with two pyridyl moieties from two ligands in a trans position (N−Ag−N = 159.7(2)°). The weak Ag···OH2 interaction (2.98(1) Å) might be attributed to the deviation from the ideal linear arrangement. Thus, the basic structure is a 2D network consisting of hexagonal (Ag6L6) motifs. Nitrite anions act as counteranions rather than anionic ligands (the shortest distance of Ag···ONO = 4.86(1) Å). The most interesting feature is that the 2D structures are stacked in an eclipsed mode along the c-axis (interlayer distance 5.33(1) Å), resulting in the formation of molecular suprachannels of 5.2 × 7.3 Å2 dimensions. The solvate water molecules are positioned in the suprachannel along with the nitrite anions; their orientation and interactions are depicted in Figure 2. Three nitrite anions and eight water molecules form, via many hydrogen bonds (1.56−2.82 Å), a cluster that is connected to adjacent clusters via other hydrogen bonds (2.27 Å), thus forming a 1D columnar aggregate of water molecules and nitrite anions. The correlation between the 1D columnar aggregates and the 2D coordination framework might be an important factor affecting the construction of desirable porous materials. That is, the clusters’ 1D columnar aggregates, consisting of solvate water molecules and nitrite counteranions, possibly are the driving force behind the eclipsed-mode stacking of the 2D coordination networks and the resultant generation of the unique suprachannels. The structure of [Ag3L2(H2O)2](NO3)3·4CH3OH·4H2O is very similar to that of [Ag3L2(H2O)2](NO2)3·10H2O, except the solvate molecules. The interlayer distance between the 2D hexagonal (Ag6L6) networks is 4.39(1) Å. Three nitrate anions (the shortest distance of Ag···ONO2 = 2.85(2) Å), four water molecules, and four methanol molecules form a cluster via hydrogen bonds (1.72−2.67 Å). The cluster is connected to the adjacent clusters via other hydrogen bonds (1.72 Å), thus forming a 1D columnar aggregate. The suprachannel size (6.2 × 7.7 Å2) of [Ag3L2(H2O)2](NO3)3·4CH3OH·4H2O is slightly larger than that of [Ag3L2(H2O)2](NO2)3·10H2O (Figure 1). The basic structure of [Ag3(NO3)2L2](NO3)·C2H5OH· 3H2O is a hexagonal (Ag6L6) 2D network. There are two kinds of silver(I) ions: three-coordinated and two-coordinated (Supporting Information). The three-coordinated silver(I) ion is connected to two pyridyl moieties from two ligands in a trans position (Ag−N = 2.183(6) and 2.187(7) Å; N−Ag−N =

Figure 2. (a) Space-filling structure showing solvate molecules and counteranions within the suprachannel for [Ag3L2(H2O)2](NO2)3· 10H2O (left) and [Ag3L2(H2O)2](NO3)3·4CH3OH·4H2O (right). (b) Top and (c) side views of ball-and-stick structures. The dashed lines represent the hydrogen bonds.

Table 2. Relevant Bond Lengths (Å) and Angles (deg) for [Ag3L2(H2O)2](NO2)3·10H2O, [Ag3L2(H2O)2](NO3)3·4CH3OH· 4H2O, and [Ag3(NO3)2L2](NO3)·C2H5OH·3H2O [Ag3L2(H2O)2](NO2)3·10H2O

[Ag3L2(H2O)2](NO3)3·4CH3OH·4H2O

[Ag3(NO3)2L2](NO3)·C2H5OH·3H2O

Ag(1)−N(1) Ag(1)−N(5)a Ag(1)−O(1) Ag(1)−O(8) Ag(2)−N(3) Ag(2)−N(3)b

2.203(5) 2.206(5) 2.573(5) 2.571(9) 2.31(1) 2.11(1)

Ag(1)−N(1) Ag(1)−N(5)c Ag(1)−O(1) Ag(1)−O(4) Ag(2)−N(3) Ag(2)−N(3)d

2.206(6) 2.200(6) 2.613(5) 2.553(6) 2.30 (1) 2.19(1)

Ag(1)−N(1) Ag(1)−N(3)e Ag(1)−O(4) Ag(2)−N(2) Ag(2)−N(2)f

2.187(7) 2.183(6) 2.39(3) 2.118(7) 2.296(7)

N(1)−Ag(1)−N(5)a N(1)−Ag(1)−O(1) N(1)−Ag(1)−O(8) O(1)−Ag(1)−O(8) N(3)−Ag(2)−N(3)b

156.0(2) 112.7(2) 97.1(3) 90.9(2) 159.7(2)

N(1)−Ag(1)−N(5)c N(1)−Ag(1)−O(1) N(1)−Ag(1)−O(4) O(1)−Ag(1)−O(4) N(3)−Ag(2)−N(3)d

156.3(2) 122.0(2) 98.0(2) 89.4(2) 150.8(2)

N(1)−Ag(1)−N(3)e N(1)−Ag(1)−O(4) N(3)e−Ag(1)−O(4) N(2)−Ag(2)−N(2)f

162.9(2) 70.0(6) 111.4(8) 164.1(1)

−x + 1/2, y − 1/2, −z − 1/2. b−x + 1, −y, −z + 1. c−x + 1/2, y − 1/2, −z + 1/2. d−x + 1, −y + 1, −z + 2. e−x + 1, y + 1/2, −z + 1/2. f−x, −y + 1, −z + 1. a

1891

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in the Supporting Information), with methanol, the suprachannel structure showed relatively strong quenching effects (79.8% quenching) compared with those of the semisuprachannel (73.0% quenching). And with 2-propanol, the relative quenching effects were in the reverse order (suprachannel, 65.4%; semisuprachannel, 71.4%). These results indicate that substrate sizes and space-confinement effects seem to contribute to the interaction between the suprachannel or semisuprachannel structure and the substrates. Such a fact suggests that the −OH group interacts with the silver(I) ions. Of course, the intrinsic characteristics of the ligand will play a pivotal role in the PL mechanism of the present silver(I) complexes. The emission can be assigned to the LMCT band. The increase of luminescence in the d10 Ag(I) complex might be attributable to the coordination of the ligand to the silver(I) ion, which enhances the rigidity of the ligand and thus reduces the loss of energy though the nonradioactive relaxation process.49 Anion Exchange. For the purposes of an investigation into the nature of counteranions within the suprachannel structures,50,51 anion exchange was conducted either in water or in a mixture of water and methanol (1:1). The anion exchange of [Ag3L2(H2O)2](NO3)3·4CH3OH·4H2O with NaNO2 in a 1:3 mole ratio in the mixture of water and methanol showed that the NO3− anions were completely exchanged with the NO2− anions within 1 h. The exchange process was monitored with reference to the anions’ characteristic IR frequencies. As plotted in Figure 4, the intense NO3− band at 1383 cm−1 disappeared, and the NO2− band at 1274 cm−1 appeared. The other peaks of the spectrum remained virtually unchanged, suggesting that the skeleton was retained after the anion exchange. Such maintenance of structural integrity upon anion exchange can be attributed to the significant robustness of the suprachannel structure. The reverse anion exchange, that of [Ag3L2(H2O)2](NO2)3· 10H2O with NO3− in the same mole ratio, was very slow: only about 70% of the nitrite anions were exchanged with the nitrate anions after 36 h (Figure 4). Correspondingly, whereas the anion exchange of [Ag3L2(H2O)2](NO3)3·4CH3OH·4H2O with NaNO2, in a 1:3 mole ratio in an aqueous medium, was completed within 12 h, the reverse exchange was only 70% completed after 36 h (Supporting Information). Thus, anion exchange seems to be strongly affected by subtle metallophilicity and solubility differences among species.34 The nitrite anion is known to be more metallophilic than the nitrate anion,34 and their solubility difference was confirmed by their above-noted exchange in a mixture of water and methanol (1:1) (Figure 4). This result, moreover, is consistent with the solubility of [Ag3L2(H2O)2](NO3)3·4CH3OH·4H2O in methanol. Another important driving force of the anion exchange, of course, is the [Ag3L2(H2O)2](NO2)3·10H2O:NaNO3 mole ratio.

162.9(2)°) and to one oxygen atom from a nitrate anion (Ag− O = 2.39(3) Å), in a T-shaped arrangement; the twocoordinated silver(I) ion is coordinated to two pyridyl moieties from two ligands in a trans position (Ag−N = 2.118(7) and 2.296(7) Å; N−Ag−N = 164.1(1)°). It is noteworthy that the 2D networks are arranged in a staggered abab... mode with an interlayer distance of 4.44(1) Å (Supporting Information), resulting in the formation of 3.1 × 5.1 Å2 semisuprachannels (Figure 1). Two water molecules, one ethanol molecule, and the remaining nitrate counteranion (the shortest Ag···ONO2 = 3.25(3) Å) form a cluster via hydrogen bonds (2.01−2.52 Å). In other words, the number of solvate molecules and the size of the cluster can be subtly manipulated in forming a molecular array. According to the classification of structural diversity of the complexes, the three coordination polymers can be described as I0O2 type, namely, layered coordination polymers, in which In and On (n = 0−3) refer to the dimensionality of inorganic connectivity and metal−organic−metal connectivity, respectively.42 Photoluminescence Spectra. A number of d10 silver(I) coordination polymers have been known to exhibit intense luminescence properties via closed-shell argentophilic (d10− d10) interactions43−45 or ligand-to-metal charge transfer (LMCT).46−48 L, upon excitation at 255 nm, exhibits an emission band with a λmax at 400 nm. [Ag3L2(H2O)2](NO2)3· 10H 2 O, [Ag 3 L 2 (H 2 O) 2 ](NO 3 ) 3 ·4CH 3 OH·4H 2 O, and [Ag3(NO3)2L2](NO3)·C2H5OH·3H2O show emission bands at 399, 365, and 366 nm, respectively. Thus, to determine the molecular recognition difference between the suprachannel and semisuprachannel structures, aliphatic alcohols, namely, methanol, 1-propanol, and 2-propanol, were employed in series as substrate molecules. Upon gradual addition of alcohols to aqueous suspensions of the suprachannel ([Ag3L2(H2O)2](NO3)3·4CH3OH·4H2O) and semisuprachannel ([Ag3(NO3)2L2](NO3)·C2H5OH·3H2O) structures, distinctly different PL changes were observed. Whereas with 1-propanol both structures showed significant quenching effects (suprachannel, 90.9%; semisuprachannel, 81.9%; Figure 3; Figure S6

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CONCLUSION Self-assembly of silver(I) ions with a C3-symmetric N,N′,N″tris(2-pyridinylethyl)-1,3,5-benzenetricarboxamide tectonic gives rise, via a molecular array of 2D hexagonal networks, to a novel suprachannel or semisuprachannel structure. In the molecular stacking of those networks, the solvent plays a significant role. This is a good example of the exhibited subtle competition between water molecules and nitrate or nitrite anions to coordinate with the silver(I) ion. This series of silver(I) complexes displays photoluminescent properties in the

Figure 3. Relative PL intensity of (a) [Ag3L2(H2O)2](NO3)3· 4CH3OH·4H2O and (b) [Ag3(NO3)2L2](NO3)·C2H5OH·3H2O suspended in water (1 mL) versus the amounts of methanol (black), 1-propanol (red), and 2-propanol (blue). Representative PL spectra of [Ag3L2(H2O)2](NO3)3·4CH3OH·4H2O upon addition of 1-propanol are plotted in Figure S5 (Supporting Information). Inset: photographs of respective crystalline solids suspended in water showing quenching phenomena resulting from 1-propanol addition. 1892

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NaNO2 in an aqueous solution, and CIF data. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: +83-52-516-7421. Phone: +82-51-510-2591. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean Government (MEST) (2013R1A2A2A07067841).

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Figure 4. IR spectra showing anion exchange of (a) [Ag3L2(H2O)2](NO2)3·10H2O with 3 equiv of NaNO3 and (b) [Ag3L2(H2O)2](NO3)3·4CH3OH·4H2O with 3 equiv of NaNO2 in a mixture of H2O/ MeOH solution (1:1, v/v; right). The blue and red arrows indicate the characteristic IR bands for nitrite and nitrate anions, respectively.

blue region. Thus, such molecular suprachannel materials can be very useful in chemosensing and anion exchange applications. Further study of this series of coordination suprachannel frameworks based on such tridentate N-donors, now under way, hopefully will uncover a systematic strategy for the design and construction of metal−organic frameworks (MOFs) with new topologies and potential gas separation and adsorption applications.

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REFERENCES

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ASSOCIATED CONTENT

S Supporting Information *

ORTEP drawings for [Ag 3 L 2 (H 2 O) 2 ](NO 2 ) 3 ·10H 2 O, [Ag3L2(H2O)2](NO3)3·4CH3OH·4H2O, and [Ag3(NO3)2L2](NO3)·C2H5OH·3H2O, packing diagram for [Ag3(NO3)2L2](NO3)·C2H5OH·3H2O, 1H NMR (CD3OD) spectra and photoluminescence spectra in methanol of L and [Ag3L2(H2O)2](NO3)3·4CH3OH·4H2O, FAB mass data of [Ag3L2(H2O)2](NO3)3·4CH3OH·4H2O, TGA curves and SEM images of thermal residues for [Ag3L2(H2O)2](NO3)3· 4CH3OH·4H2O and [Ag3(NO3)2L2](NO3)·C2H5OH·3H2O, PL spectra for [Ag3L2(H2O)2](NO3)3·4CH3OH·4H2O upon addition of 1-propanol, IR spectra showing anion exchange of [Ag3L2(H2O)2](NO2)3·10H2O with 3 equiv of NaNO3 and of [Ag3L2 (H2 O)2 ](NO 3)3 ·4CH 3OH·4H2O with 3 equiv of 1893

dx.doi.org/10.1021/cg500025k | Cryst. Growth Des. 2014, 14, 1888−1894

Crystal Growth & Design

Article

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