Infinite Water Chains Trapped in an Organic Framework Constructed

CRYSTAL GROWTH & DESIGN

Infinite Water Chains Trapped in an Organic Framework Constructed from Melamine with 1,5-Naphthalenedisulfonic Acid via Hydrogen Bonds

2005 VOL. 5, NO. 4 1609-1616

Xiu-Lian Zhang,†,‡ Bao-Hui Ye,*,† and Xiao-Ming Chen*,† School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, P. R. China, and Department of Chemistry, Guangdong Institute of Education, Guangzhou 510310, P. R. China Received March 16, 2005;

Revised Manuscript Received April 11, 2005

ABSTRACT: Cocrystallizations of melamine (MA) with 1,5-naphthalenedisulfonic acid (H2NDA) from water in different molar ratios (2:1, 4:1, and 8:1) offer [(HMA+)2(NDA2-)]‚4H2O (1), [(HMA+)2(MA)2(NDA2-)]‚8H2O (2), and [(HMA+)2(MA)2(NDA2-)]‚10H2O (3), respectively. Among them, sulfonic protons are transferred to the triazine nitrogen atoms of MA, furnishing hydrogen-bonded anionic [(NDA2-)‚H2O]∞ chains. In 1, the adjacent HMA+ cations form cationic (HMA+)∞ ribbons via pairs of N-H‚‚‚N hydrogen bonds (R22(8) synthon), and the ribbons connect to each other through NDA2- anions as well as lattice water molecules via hydrogen bonds and C-H‚‚‚π, π‚‚‚π, and electrostatic interactions to form a 3D structure. In 2 and 3, only half of the MA molecules are protonated, resulting in cationic (MA‚HMA+)∞ ribbons via N-H‚‚‚N hydrogen bonds. In 2, hydrophilic channels (size 3.9 × 6.1 Å2) enclosed by the NDA2- anions and (MA‚HMA+) cations are found to host a pair of zigzag water chains, which are interlinked through sulfonate oxygen atoms via hydrogen bonds into a double water chain. In 3, similar 1D channels are also found to accommodate a pair of water chains in each channel via hydrogen bonds. Introduction Rational control of molecular self-assembly is critical yet difficult for intelligent crystal engineering.1 Many attempts to control the structures in the solid state have focused on crystal engineering via hydrogen-bonding and electrostatic interactions because they possess interesting electronic properties such as nonlinear optical behavior, conductivity, and superconductivity. As an excellent hydrogen donor and hydrogen acceptor, melamine (MA) has been employed in constructing supramolecular architectures,2 such as ribbons, sheets, rectangular nets, and organic-inorganic sandwich-type 3D networks with barbituric acid, succinimide, cyanuric acid, 4,4′-bipyridyl, and nitrilotriacetic acid.3-10 The sulfonate group is an excellent candidate for hydrogen acceptor and has been widely used in crystal engineering with guanidinium as molecular storage materials.11-14 A survey of the CSD15 revealed that 31 MA complexes have been documented with X-ray single-crystal determinations and only two examples of cocrystals of MA with sulfonate and aryl sulfonate bis(4-hydroxybenzenesulfonate) have been reported.16 This stimulates us to construct supramolecular architectures of MA and 1,5-naphthalenedisulfonic acid (H2NDA), which would be expected to exhibit diversified hydrogen-bonding modes and interesting architectures. Moreover, water chains are of great interest, since many fundamental biological processes appear to depend on the unique properties of water chains.17 Structural studies have shown that water chains exist in gramicidin A membrane channels,18 bacteriorhodopsin,19 and R-amylase20 for rapid transport of protons and act as “proton wires”. Observations of water chains in organic hosts exhibiting supramolecular interactions have significantly ad† ‡

Sun Yat-Sen University. Guangdong Institute of Education.

vanced the understanding of structures and functions of water chains in biological systems.21 As a sequel work of our investigation on cocrystals of MA and aromatic carboxylic acids,21h we report herein the structures of cocrystals of MA with H2NDA in different molar ratios from water solution, resulting in [(HMA+)2(NDA2-)]‚4H2O (1), [(HMA+)2(MA)2(NDA2-)]‚8H2O (2), and [(HMA+)2(MA)2(NDA2-)]‚10H2O (3), in which a pair of water chains were trapped in the hydrophilic channels enclosed by the NDA2- anions and (MA‚HMA+) cations, and further stabilized via hydrogen bonds in 2 and 3. Experimental Section Materials and Methods. All the reagents and solvents employed were commercially available and used as received without further purification. The C, H, and N microanalyses were carried out with a Perkin-Elmer 240 elemental analyzer. The FT-IR spectra were recorded from KBr pellets in the range 4000-400 cm-1 with a Nicolet 5DX spectrometer. Thermogravimetric data were collected on a Netzsch TG-209 analyzer in nitrogen at a heating rate of 10 °C min-1. Syntheses. Compounds 1-3 were prepared by mixing hot aqueous solutions of MA (0.126 g, 1 mmol) and H2NDA in different molar ratios of 2:1, 4:1, and 8:1, for 1, 2, and 3, respectively. The hot mixtures were stirred at room temperature and filtered. After a few days, colorless crystals of 1-3 were deposited from the filtrates. a. [(HMA+)2(NDA2-)]‚4H2O (1). Yield: 0.28 g, 91% based on H2NDA. Anal. Calcd for C16H28N12O10S2 (1): C, 31.37; H, 4.61: N, 27.44. Found: C, 31.34; H, 4.56; N, 27.45. IR (KBr, cm-1): 3374-2699 (br, OsH, NsH), 3080 (aromatic CsH), 1672 (CdN), 1623, 1503 (aromatic, s, CdC), 1185, 1154, 1036 (SdO), 797, 772, 614 (aromatic CsH). b. [(HMA+)2(MA)2(NDA2-)]‚8H2O (2). Yield: 0.20 g, 87% based on H2NDA. Anal. Calcd for C22H48N24O14S2 (2): C, 28.19; H, 5.16: N, 35.88. Found: C, 28.29; H, 5.19; N, 35.81. IR (KBr, cm-1): 3469-3133 (br, OsH, NsH), 3085 (aromatic CsH), 1677 (CdN), 1647, 1557, 1541 (aromatic, s, CdC), 1092, 1035 (SdO), 815, 770, 616 (aromatic CsH).

10.1021/cg050096e CCC: $30.25 © 2005 American Chemical Society Published on Web 05/18/2005

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Table 1. Crystallographic Data and Structure Refinement Parameters for 1-3 formula Mr crystal color crystal size (mm3) crystal system space group a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) Dc (g cm-3) Z no. of data/params µ (mm-1) θ range (deg) h range k range l range reflns collected ind reflns obs reflns R1 [I > 2σ(I)] wR2 (all data) GOF

1

2

3

C16H28N12O10S2 612.64 colorless 0.17 × 0.11 × 0.10 triclinic P1 h 6.9323(6) 12.357(1) 16.648(2) 72.266(2) 85.010(2) 77.851(2) 1327.5(2) 1.533 2 5171/441 0.275 1.28-25.99 -8 to 8 -15 to 15 -20 to 20 10506 5171 3702 0.0582 0.1608 1.078



Scheme 1. Ribbons Constructed by MA-MA (a), MA-HMA+ (b), and HMA+-HMA+ (c) via R22(8) Hydrogen-Bonded Synthons

c. [(HMA+)2(MA)2(NDA2-)]‚10H2O (3). Yield: 0.22 g, 89% based on H2NDA. Anal. Calcd for C22H52N24O16S2 (3): C, 27.15; H, 5.39: N, 34.56. Found: C, 27.10; H, 5.36; N, 34.60. IR (KBr, cm-1): 3500-3000 (br, OsH, NsH), 3085 (aromatic CsH), 1668 (CdN), 1653, 1576, 1558 (aromatic, s, CdC), 1044 (Sd O), 813, 611 (aromatic CsH). X-ray Crystallography. Intensities data for 1-3 were collected at 293 K on a Bruker SMART Apex CCD diffractometer, and the data reductions were performed using Bruker SAINT.22a The structures were solved by direct methods and refined with the full-matrix least squares on F2 with anisotropic displacement parameters for non-H atoms using SHELXTL.22b The hydrogen atoms of the water molecules and the protonated aromatic nitrogen atoms of the MA molecules are located from the difference Fourier maps, and the other hydrogen atoms were generated geometrically (C-H, 0.96 Å;

N-H, 0.90 Å) for 1-3. The structural plots were drawn using SHELXTL and Mercury.23 Crystal data as well as details of data collection and refinement for the complexes are summarized in Table 1. Selected bond distances and bond angles are listed in Tables 2-4.

Results and Discussion Synthesis. The crystal structure of MA has been reported to exhibit a ribbon linked via the R22(8) hydrogen-bonded synthon,24 as shown in Scheme 1a. When acid was introduced, the MA molecule may have been protonated to form a cationic ribbon.25 Indeed, when MA and H2NDA were mixed in a 2:1 molar ratio in a hot aqueous solution, 1 was obtained, in which one triazine

Infinite Water Chains Trapped in an Organic Framework Table 2. Selected Hydrogen-Bonding Parameters for 1 D-H‚‚‚Aa

D‚‚‚A (Å)

D-H (Å)

H‚‚‚A (Å)

D-H‚‚‚A (deg)

N11-H11A‚‚‚O2wb N11-H11C‚‚‚O3c N5-H5NB‚‚‚N10d N5-H5NA‚‚‚O1e N4-H4‚‚‚O3w N3-H3NA‚‚‚N12 N3-H3NB‚‚‚O2wf N1-H1NB‚‚‚O1wg N1-H1NA‚‚‚O6 N8-H8‚‚‚O4w N9-H9NB‚‚‚N6h N7-H7NB‚‚‚O1wi N9-H9NA‚‚‚O6j N7-H7NA‚‚‚N2 O1w-H1wA‚‚‚O1 O3w-H3wA‚‚‚O5k O2w-H2wB‚‚‚O4 O1w-H1wB‚‚‚O2l O4w-H4wA‚‚‚O3m O2w-H2wA‚‚‚O6n O4w-H4wB‚‚‚O4o C16-H16A‚‚‚O2p

2.912(4) 2.967(3) 2.984(4) 2.868(4) 2.670(4) 2.992(4) 2.878(4) 2.927(4) 3.018(4) 2.662(4) 2.981(4) 2.926(4) 2.946(4) 2.995(4) 2.785(5) 2.721(4) 2.778(4) 2.802(4) 2.763(5) 2.826(4) 2.835(5) 3.484(4)

0.86 0.86 0.80(3) 0.90(3) 0.91(3) 0.86(3) 0.96(3) 0.85(3) 0.85(3) 0.90(4) 0.86(4) 0.99(4) 0.87(3) 0.75(3) 0.76(4) 0.89(6) 0.78(5) 0.84(6) 0.95(7) 0.79(6) 0.69(6) 0.93(3)

2.06 2.21 2.19(3) 1.99(3) 1.77(3) 2.14(4) 2.17(3) 2.08(3) 2.18(3) 1.78(4) 2.12(4) 2.18(4) 2.33(3) 2.25(4) 2.08(4) 1.84(6) 2.04(5) 1.98(6) 1.95(7) 2.10(5) 2.21(7) 2.56(5)

170.6 146.4 178(3) 164(3) 173(3) 174(3) 130(2) 173(3) 168(3) 169(4) 176(3) 132(3) 128(3) 172(4) 154(4) 168(5) 158(5) 169(6) 143(6) 154(6) 150(8) 173.9(4)

Symmetry codes: (b) x + 1, -y + 2, -z + 1; (c) -x + 1, -y + 2, -z + 1; (d) x, y - 1, z; (e) -x + 1, -y + 1, -z + 1; (f) -x + 1, -y + 2, -z + 1; (g) x, y + 1, z; (h) x, y + 1, z; (i) x, y + 1, z; (j) x, y + 1, z; (k) -x + 1, -y + 2, -z + 1; (l) x + 1, y, z; (m) x + 1, y + 1, z; (n) x - 1, y, z; (o) x, y + 1, z; (p) 1 - x, 1 - y, -z. a

Table 3. Selected Hydrogen-Bonding Parameters for 2 D-H‚‚‚Aa N3-H3A‚‚‚N12b N5-H5B‚‚‚O3wc N7-H7A‚‚‚O3 N7-H7B‚‚‚N6d N9-H9A‚‚‚O2e N9-H9B‚‚‚O4wf N10-H10‚‚‚O2wg N11-H11A‚‚‚N4h N11-H11B‚‚‚O3wi O1w-H1wB‚‚‚O1j O2w-H2wB‚‚‚O4w O2w-H2wA‚‚‚O1wk O3w-H3wA‚‚‚O3l O3w-H3wB‚‚‚O2 O4w-H4wA‚‚‚O1w O4w-H4wB‚‚‚O1m O1w-H1wA‚‚‚N2

D‚‚‚A (Å) D-H (Å) H‚‚‚A (Å) 3.099(4) 3.021(4) 2.975(3) 2.963(3) 2.955(3) 3.091(4) 2.752(4) 2.907(4) 2.844(4) 2.836(3) 2.818(5) 2.841(5) 2.902(4) 2.813(4) 2.909(5) 2.857(4) 2.744(4)

0.86 0.86 0.86 0.86 0.86 0.86 0.85(1) 0.86 0.86 0.85(1) 0.86(5) 0.77(7) 0.82(6) 0.83(5) 0.80(4) 0.86(5) 0.85(1)

2.24 2.19 2.20 2.12 2.28 2.26 1.91(1) 2.05 2.12 2.02(3) 2.01(5) 2.12(7) 2.09(6) 2.02(5) 2.15(5) 2.00(6) 1.90(1)

Crystal Growth & Design, Vol. 5, No. 4, 2005 1611 Table 4. Selected Hydrogen-Bonding Parameters for 3 D-H‚‚‚Aa

D‚‚‚A (Å) D-H (Å) H‚‚‚A (Å)

N1-H1A‚‚‚N12 N1-H1B‚‚‚O3wb N2-H2‚‚‚O1wc N3-H3A‚‚‚O5w N3-H3B‚‚‚O1wd N5-H5B‚‚‚N10e N5-H5A‚‚‚O1 N7-H7B‚‚‚N6 N11-H11A‚‚‚N4f N11-H11B‚‚‚O5wg O1w-H1wA‚‚‚O2w O1w-H1wB‚‚‚O4wh N2-H2‚‚‚O1w N3-H3B‚‚‚O1w O2w-H2wB‚‚‚N8m O4w-H4wB‚‚‚O2w O4w-H4wA‚‚‚O2i O3w-H3wA‚‚‚O3j O3w-H3wB‚‚‚O2 O5w-H5wA‚‚‚Owk O5w-H5wB‚‚‚O1l

3.052 (3) 2.895(4) 2.882(4) 2.982(4) 2.869(4) 3.019(3) 2.848(3) 3.072(3) 3.018(3) 2.921(3) 2.866(5) 2.754(4) 2.882(4) 2.869(4) 2.849(4) 2.749(4) 2.751(4) 2.779(3) 2.855(4) 2.810(4) 3.071(4)

0.86 0.86 0.95(4) 0.86 0.86 0.86 0.86 0.86 0.86 0.86 0.78 0.88 0.953 0.86 1.00 0.991 0.85 0.86 0.85 0.86 0.85

2.20 2.04 2.10(4) 2.14 2.09 2.17 2.15 2.24 2.17 2.25 2.09(6) 1.90(6) 2.012 2.093 1.86(3) 1.852(2) 2.01(3) 1.95(2) 2.01(1) 1.96 (1) 2.27(2)

D-H‚‚‚A (deg) 170.0 175.8 151(3) 164.4 149.8 168.0 138.3 162.3 170.1 134.8 172(6) 165(5) 151(5) 150(4) 172(3) 149(3) 146(4) 161(5) 175(5) 171(4) 157(3)

a Symmetry codes: (b) -x + 3, -y + 2, -z; (c) -x + 2, -y + 2, -z; (d) -x + 2, -y + 2, -z; (e) x, y + 1, z; (f) x, y - 1, z; (g) x, y 1, z; (h) x - 2, y, z; (i) x - 3, y, z; (j) x + 1, y, z; (k) -x + 3, -y + 3, -z; (l) -x + 2, -y + 2, -z + 1; (m) x, y + 1, z.

Scheme 2.

Synthesis of 1-3 in Different Molar Ratios

D-H‚‚‚A (deg) 176.3 162.5 150.8 166.0 135.4 161.6 170(4) 177.3 142.0 160(6) 155(5) 157(7) 173(6) 159(5) 158(4) 176(4) 175(5)

a Symmetry codes: (b) -x + 2, -y + 2, -z + 1; (c) x + 1, y, z + 1; (d) -x + 3, -y + 1, -z + 1; (e) -x + 2, -y + 1, -z; (f) x, y, z 1; (g) x, y, z - 1; (h) -x + 2, -y + 2, -z + 1; (i) -x + 1, -y + 2, -z; (j) -x + 1, -y + 2, -z + 1; (k) x - 1, y, z; (l) x - 1, y, z; (m) x + 1, y, z.

nitrogen atom of MA was protonated to give a cationic (HMA+)∞ ribbon (Scheme 1c). To observe the effect of acid on the cationic ribbon, low acid concentration was also examined. When the molar ratio of MA to H2NDA was increased to 4:1, only half of the MA molecules were protonated, furnishing a cationic (MA‚HMA+)∞ ribbon (Scheme 1b). This structural feature is very different from that of 1, attributable to the acidity tuning. Moreover, when the molar ratio was up to 8:1, the ribbons in 2 could also be generated, but concomitant with more lattice water molecules, as revealed in the case of 3. After isolation of the crystals of 3, the crystals of MA mixing with 3 were obtained when the filtrate was concentrated upon solvent evaporation at room temperature. The reactions were summarized in Scheme 2. It is worthy of mention that using other polar

solvents, such as MeOH/H2O (v/v 1:1) and EtOH/H2O (v/v 1:1) gave the same corresponding compounds. Crystal Structures. In 1, the H2NDA molecules are deprotonated and MA molecules are protonated. One triazine nitrogen atom of MA is protonated, leading to an enhancement of the internal bond angles of C2-N4C3 ) 119.7(2)° and C4-N8-C5 ) 119.5(2)° compared with the case of the neutral MA (113.9-114.6(2)°) in 2 and 3. This phenomenon was also observed in TMPsulfonate complexes (TMP ) trimethoprim).26 The adjacent HMA+ cations related by an inverse center are joined by pairs to form undulate ribbons (Figure 1) running along the b-axis via a pair of N-H‚‚‚N hydrogen bonds (N5‚‚‚N10c ) 2.984(4) Å, N3‚‚‚N12 ) 2.992(4) Å, N7‚‚‚N2 ) 2.995(4) Å, and N9‚‚‚N6g ) 2.981(4) Å). Adjacent (HMA+)∞ ribbons are interconnected by NDA2anions in a head-to-head fashion via hydrogen bonds of R23(8) (O6‚‚‚N1 ) 3.018(4) Å and O6ib‚‚‚N9 ) 2.946(4) Å) and R33(10) (O1d‚‚‚N5 ) 2.868(4) Å and O3b‚‚‚N11 ) 2.967(3) Å) motifs to generate corrugated layers parallel to the bc plane. Interestingly, the sulfonate O6 atom of NDA2- bridges two amino hydrogen atoms from two different HMA+ cations, forming a hydrogen pattern with an R23(8) ring motif, while the sulfonate O1 and O3 atoms connect two amino hydrogen atoms from two different HMA+ cations, generating a hydrogen-bonding pattern of R33(10). Meanwhile, the lattice molecules (O1w and O2w) are anchored on the layer via hydrogen-bonded ring motif R23(8) (O1wh‚‚‚N7 ) 2.926(4) Å, O1wf‚‚‚N1 ) 2.927(4) Å, O2wa‚‚‚N11 ) 2.912(4) Å, and O2we‚‚‚N3 ) 2.878(4)

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Figure 1. View of the (HMA+)∞ ribbons (along the b-axis) extended into a layer structure (parallel to the bc plane) via hydrogen bonds with NDA2- anions in 1. Figure 3. View of a [(NDA2-)‚H2O]∞ double chain (a), and the interlinking of a pair of [(NDA2-)‚H2O]∞ double chains (one green, another blue) connected by water molecules (O4w) featuring R78(22) hydrogen-bonded ring motifs (red dotted line) in 1 (b).

Figure 2. View of the hydrogen-bonded 3D network in 1 along the a-axis.

Å). These layers are stacked in ABAB fashion into a 3D structure (Figure 2) by N-H‚‚‚O, Ow-H‚‚‚O, and C-H‚ ‚‚O hydrogen bonds as well as C-H‚‚‚π interactions between the NDA2- anions (see below) and offset π‚‚‚π stacking interactions (ca. 3.39 Å) between HMA+ and HMA+ cations from adjacent layers. The distances of N-H‚‚‚Ow (2.662(4)-2.927(4) Å) and N-H‚‚‚O (2.868(4)-3.018(4) Å) hydrogen bonds are comparable to those reported in the literature (mean N‚‚‚O distance 2.946 Å).14 On the other hand, the O1w and O2w molecules in 1 are further interlinked to the NDA2- anions via hydrogen bonds (O1‚‚‚O1w ) 2.785(4) Å, O2k‚‚‚O1w ) 2.804(4) Å, O4‚‚‚O1w ) 2.778(4) Å, and O6m‚‚‚O2w ) 2.836(4) Å) into anionic [(NDA2-)‚H2O]∞ double chains running along the a-axis (Figure 3). These double chains are interconnected by O4w molecules, giving rise to 22-membered hydrogen-bonded R78(22) ring motifs (O4w‚‚‚O2l ) 2.763(5) Å and O4w‚‚‚O4n ) 2.835(5) Å), as shown in Figure 3b. In contrast, the O3w molecule only interacts with one chain via a O3w‚‚‚O5j (2.724(4) Å) hydrogen bond. The dihedral angle of two adjacent naphthalene rings is 22.4°. Careful examination of the supramolecular interaction of NDA2- anions reveals that other weak intermolecular interactions, such as

Figure 4. 2D NDA2- network constructed via weak interactions C-H‚‚‚O and C-H‚‚‚π on the ab plane in 1.

Figure 5. View of the 2D network constructed via hydrogen bonds parallel to the bc plane in 2.

Infinite Water Chains Trapped in an Organic Framework

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Figure 6. 3D structure of 2 viewed along the a-axis. The circles highlight the 1D hexagonal channels filled with a pair of zigzag water chains. The inset plot shows the pair of zigzag chains (in space filling) running along the a-axis and their environment.

Figure 7. View of the hydrogen-bonded motifs R46(12) (purple dotted lines) and R68(16) (red dotted lines) (a) and the pair of zigzag water chains filling in the hydrophilic channels (b) in 2.

C-H‚‚‚O (3.486(3) Å) and C-H‚‚‚π (3.321 Å), are also present in 1, which connect the NDA2- anions into a 2D network parallel to the ab plane, as shown in Figure 4. In 2, only half of the MA molecules are protonated and arranged alternately via R22(8) ring motifs, each composed of a pair of N-H‚‚‚N hydrogen bonds (N3‚‚‚ N12a ) 3.099(4) Å, N4g‚‚‚N11 ) 2.907(4) Å, N6c‚‚‚N7 ) 2.963(3) Å, and N5‚‚‚N8 ) 3.119(3) Å), resulting in cationic (MA‚HMA+)∞ ribbons (Figure 5) extending in the b-direction. These ribbons are further interlinked by the NDA2- anions via hydrogen bonds into a highly corrugated layer parallel to the bc plane, as shown in Figure 5. One interesting feature is the saddle-like

Figure 8. View of the hydrogen-bonded 2D network on the bc plane in 3.

cavities (11.1 × 10.0 × 6.5 Å3) present in these layers and occupied by lattice water molecules. Such water molecules are hydrogen-bonded to the layer, resulting in the hydrogen-bonded ring motifs of R23(8) (O3‚‚‚N7 ) 2.975(3) Å, O2d‚‚‚N9 ) 2.955(3) Å), R46(12) (O1l‚‚‚O4w ) 2.857(4) Å and O1w‚‚‚O4w ) 2.909(5) Å), and R55(14) (O1i‚‚‚O1w ) 2.836(3) Å and O1w‚‚‚O2wj ) 2.841(5) Å). The sulfonate O2 and O3 atoms are orientated in an almost vertical fashion to the bc plane and are interlinked by water O3w molecules via hydrogen bonds (O2‚ ‚‚O3w ) 2.813(4) Å and O3k‚‚‚O3w ) 2.902(4) Å) into anionic [(NDA2-)‚H2O]∞ double chains along the a-axis,

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Figure 9. 3D structure of 3 viewed along the a-axis. The circle highlights the 1D hydrophilic channel filling with a pair of zigzag water chains.

Figure 10. Water molecules in the zigzag water chains are hydrogen-bonded to the -SO3- groups via three center (red dotted lines) and O-H‚‚‚O (purple dotted lines) hydrogen bonds in 3.

being similar to those found in 1 (Figure 4a), which extend the layers into a 3D structure, as shown in Figure 6. In the 3D structure of 2, the most unusual feature is a hexagonal hydrophilic channel running along the a-axis with a size of 3.9 × 6.1 Å2 (Figure 6), being enclosed by the NDA2- anions and (MA‚HMA+) cations. A pair of hydrogen-bonded zigzag water chains are accommodated in each channel, as shown in Figure 7. Each water chain consists of three independent water molecules O1w, O2w, and O4w, interlinked by hydrogen bonds (O1w‚‚‚O4w ) 2.909(5) Å, O2w‚‚‚O1w ) 2.841(5) Å, and O2w‚‚‚O4w ) 2.818(5) Å), in which the O2w molecule acts as a double-hydrogen-bond donor while O1w and O4w function as both hydrogen-bond donors

and acceptors. Moreover, the pair of zigzag water chains are interlinked by the sulfonate O1 atom via hydrogen bonds (O1‚‚‚O4w ) 2.857(4) Å and O1‚‚‚O1w ) 2.836(3) Å), resulting in a double water chain (see Figure 7a). Although similar water chains encased by supramolecular interactions have been reported,21 in which the water molecules all act as both hydrogen-bond donors and acceptors, in 2, one water molecule acts as a doublehydrogen-bond donor while the other two act as both hydrogen-bond donors and acceptors. As a result, four water molecules and two sulfonate oxygen atoms form a twelve-membered hydrogen-bonded ring R46(12) in a chair fashion, and six water molecules and two oxygen atoms from two sulfonate groups yield a sixteen-member

Infinite Water Chains Trapped in an Organic Framework

Crystal Growth & Design, Vol. 5, No. 4, 2005 1615

hydrogen-bonded R68(16) ring. Two kinds of such rings are arranged alternately by sharing O1, O1w, and O4w in a double water chain along the a-axis. The crystal structure of 3 features similar cationic (MA‚HMA+)∞ ribbons to those in 2. Half of the MA molecules are protonated and arranged alternately via N-H‚‚‚N hydrogen bonds (N1‚‚‚N12 ) 3.052(2) Å, N4‚‚‚N11e ) 3.018(3) Å, N6‚‚‚N7 ) 3.072(3) Å, and N5‚ ‚‚N10d ) 3.019(3) Å), resulting in cationic (MA‚HMA+)∞ ribbons running along the b-axis. Owing to the presence of a different number of water molecules compared to that in 2, these ribbons in 3 are not directly interlinked by NDA2- anions uniquely via hydrogen bonds into a layer structure; instead, they are simultaneously crosslinked by both the NDA2- anions and lattice water molecules via hydrogen bonds (O1‚‚‚N5 ) 2.847(3) Å, O3w‚‚‚O2 ) 2.855(4) Å) and hydrogen-bonded ring motifs R12(6) (O1wc‚‚‚N3 ) 2.869(4) Å and O1wb‚‚‚N2 ) 2.882(3) Å), R23(8) (O5wf‚‚‚N11 ) 2.921(3) Å, O5w‚‚‚N3 ) 2.982(4) Å, and N11e‚‚‚N4 ) 3.018(3) Å), and R33(10) (O3wa‚‚‚N1 ) 2.895(4) Å, N1‚‚‚N12 ) 3.052(2) Å, O3wi‚ ‚‚O5w ) 2.810(4) Å, and O5wf‚‚‚N11 ) 2.921(3) Å) into corrugated layers parallel to the bc plane, as shown in Figure 8. The sulfonate O2 and O3 atoms are connected by a O3w molecule via hydrogen bonds (O2‚‚‚O3w ) 2.855(4) Å and O3i‚‚‚O3w ) 2.779(3) Å) to give anionic [(NDA2-)‚H2O]∞ double chains running along the a-axis similar to those found in 1 (see Figure 3a), which interlink the layers into a 3D structure, as shown in Figure 9. There are also hydrophilic channels extending along the a-axis direction, which are constituted by the NDA2anions and (MA‚HMA+) cations in 3 (Figure 9). Two zigzag water chains are filled in each channel via hydrogen bonds, as shown in Figure 10. The conformation of the water chain is different from that found in 2. Three independent water molecules (O1w, O2w, and O4w) are found in each water chain and are connected together by hydrogen bonds (O1w‚‚‚O4w ) 2.754(4) Å, O2wg‚‚‚O1w ) 2.866(5) Å, and O2wh‚‚‚O4w ) 2.749(4) Å), in which the O2w molecule acts as a doublehydrogen-bond acceptor while O1w and O4w function as hydrogen-bond donors. Each water chain is further hydrogen-bonded to double [(NDA2-)‚H2O]∞ chains via hydrogen bonds (O2k‚‚‚O4w ) 2.751(4) Å, O2w‚‚‚O2m ) 3.072(3) Å, and O2w‚‚‚O3n ) 3.070(3) Å). The differences in the structures of 1, 2, and 3 can be attributed to the protonations of MA at different acidities. Among them, 1 is related to the higher acidity condition; hence, all MA molecules are protonated and can only act as hydrogen-bonded donors to form cationic (HMA+)∞ ribbons (see Figure 1). However, both 2 and 3 are related to the lower acidities; hence, only half of the MA molecules are protonated, and 2 and 3 can act not only as hydrogen-bonded donors but also as hydrogenbonded acceptors, resulting in (MA‚HMA+)∞ ribbons. These (MA‚HMA+)∞ ribbons combine the NDA anions to enclose hydrophilic cavities which accommodate and stabilize the guest water chains by accepting hydrogen bonds (see Figures 5 and 8). Thermal Stability. Thermogravimetric analyses (TGA) were also performed to observe the thermal stability of 1-3. The TGA curves show weight losses of 10.1% in the temperature range 16-320 °C for 1, 14.1%

in the range 17-250 °C for 2, and 16.1% in the range 18-278 °C for 3, respectively, which compare well to the calculated values of 11.7% for 1, 15.3% for 2, and 18.5% for 3 of the lattice water molecules. At higher temperatures, the frameworks of the complexes were decomposed. Conclusion The crystal structures of 1-3 show that the adjacent MA molecules are arrayed in a centrosymmetrical fashion to form ribbons through pairs of N-H‚‚‚N hydrogen bonds. The resulting hydrogen-bonded ring motif R22(8) is robust and generally occurs in this system. Sulfonic protons are frequently transferred to triazine nitrogen atoms, giving rise to anionic [(NDA2-)‚H2O]∞ double chains, as well as cationic (MA‚HMA+)∞ ribbons in 2 and 3 or cationic (HMA+)∞ ribbons in 1, depending on the MA:H2NDA molar ratios. The NDA2- anion acts as a connector to extend the cationic ribbons into 3D structures via hydrogen bonds as well as electrostatic and π‚‚‚π interactions, while water molecules also play an important role in the construction of hydrogenbonded networks. In both 2 and 3, hydrophilic channels are formed by the NDA2- and MA‚HMA+ moieties, in which a pair of hydrogen-bonded zigzag water chains are accommodated. Acknowledgment. This work was supported by the NSFC (No. 20131020) and the Scientific and Technological Bureau of Guangdong Province (No. 04205405). Supporting Information Available: Crystallographic information files (CIF) of compounds. This materials is available free of charge via the Internet at http://pubs.acs.org.

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Infinite Water Chains Trapped in an Organic Framework Constructed

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