Hydrogen-Bonded Anionic Host Lattices Constructed with

Article pubs.acs.org/crystal

Hydrogen-Bonded Anionic Host Lattices Constructed with Isocyanurate and Thiourea/Urea Chi-Keung Lam,*,†,‡ Sam Chun-Kit Hau,† Chung-Wah Yau,† and Thomas C. W. Mak† †

Department of Chemistry and Centre of Novel Functional Molecules, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong SAR, People’s Republic of China ‡ School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, People’s Republic of China S Supporting Information *

ABSTRACT: A series of seven inclusion complexes containing the isocyanurate ion, thiourea/urea, and selected quaternary ammonium ions as templates, namely, (CH3)4N+C3H2N3O3−· 3(NH2)2CS·H2O (1), (CH3)4N+C3H2N3O3−·(NH2)2CS (2), (C2H5)4N+C3H2N3O3−·(NH2)2CS (3), (nC3H7)4N+C3H2N3O3−·(NH2)2CS·H2O (4), 3[(n-C4H9)4N+C3H2N3O3−]·5(NH2)2CS·3H2O (5), (C2H5)4N+C3H2N3O3−·(NH2)2CO (6) and (nC3H7)4N+C3H2N3O3−·2(NH2)2CO·H2O (7), have been prepared and characterized by X-ray crystallography. Complex (1) features a hydrogenbonded molecular cage in which two (CH3)4N+ cations can be accommodated. Complexes (2) and (7) are channel-type inclusion compounds. In (2), the thiourea sulfur atom does not participate in host lattice construction, while (7) contains several intersecting channel systems that are formed by the crosslinkage of two sets of isocyanurate−urea−water ribbons. Complexes (3)−(6) exhibit layer-type architectures. The host layers of complexes (3) and (6) are constructed by two distinct rosette motifs produced by isocyanurate ion and thiourea/urea in a ratio of 2:1 and 1:2, respectively. The isocyanurate−thiourea−water (1:1:1) ribbons are cross-linked together to generate the host framework of complex (4), while a new type of supramolecular rosette ribbon is identified in complex (5).

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INTRODUCTION

exclusively in acidic solution and is the dominant species that participates in chemical reactions.

There are two principal classes of inclusion compounds of urea/thiourea that are stabilized by conventional hydrogen bonds: the classical channel-type clathrates having a host lattice constructed from urea/thiourea molecules1,2 (Scheme 1) and those whose host lattices contain various anionic species and neutral molecules as additional components.3 Making use of urea/thiourea and selected anions such as halides, simple trigonal- and square-planar anions, mono- and dicarboxylates, as well as larger planar or nonplanar anions as molecular building blocks, together with symmetric and unsymmetric quaternary ammonium ions as templates, many new types of anionic host lattices and inclusion topologies have been generated and thoroughly investigated.4 Advances in the stabilization of labile anionic species (such as dihydrogen borate, allophanate, thioallophanate, and the valence tautomers of croconate and rhodizonate) by hydrogen-bond formation with urea/thiourea in a supramolecular network assembly, with quaternary ammonium cations serving as guest templates, have been recently reviewed.5 2,4,6-Trihydroxy-1,3,5-triazine N3(COH)3 (I), commonly named cyanuric acid (I), is among the oldest reported organic compounds. This enolized form only occurs to the extent of 5.6% in neutral solution.6 The triketo tautomer (NH)3(CO)3 (II), commonly known as isocyanuric acid, exists almost © 2016 American Chemical Society

Isocyanuric acid is slightly soluble in water: 0.125% at room temperature and 4% in boiling water.7 It can be crystallized in neat form8−11 or as a dihydrate.12 Generation of the mono-, di-, and trianionic forms at pKa values of 6.85, 10.91, and >12, respectively, was reported by Aoki et al. in 2000.13 Surprisingly, to date only 12 single-crystal X-ray structures of hydrogenbonded complexes of the ordered isocyanurate ion are documented in the Cambridge Structural Database, CSD V5.36 (November, 2014) with May 2015 update.14−26 Since isocyanuric acid is a C3-symmetric molecule that has three alternating N−H and CO hydrogen-bonding sites, it serves as an ideal building block for constructing rosette Received: September 18, 2015 Revised: January 4, 2016 Published: January 8, 2016 759

DOI: 10.1021/acs.cgd.5b01350 Cryst. Growth Des. 2016, 16, 759−773

Crystal Growth & Design

Article

Scheme 1. Typical Hydrogen-Bonding Modes of Urea/Thiourea Molecules: (a) Head-to-Tail; (b) Shoulder-to-Shoulder; (c) Designation of syn- and anti-Hydrogen Atoms

networks,27 but the isocyanuric acid−melamine 1:1 supramolecular rosette network28 is not very soluble in water. In the 1990s, Whitesides and co-workers focused on the construction of soluble molecular aggregates and crystalline materials utilizing hydrogen-bonding interactions between designed derivatives of isocyanuric acid and melamine.29,30 Later on, Reinhoudt and co-workers conducted a comprehensive study of the surface chemistry, kinetics, and supramolecular chirality of multiple rosette systems.31−44 To overcome the problem of low solubility of cyanuric acid, we decided to employ the isocyanurate monoanion in the construction of rosette structures, noting that deprotonation of one N−H group creates a hydrogen-bond accepting site. With reference to our previous studies on the construction of anionic host lattices from urea/thiourea and nitrobarbiturate,45 as well as the designed construction of rosette layers46 and linear “fusedrosette ribbon” assembled from the guanidinium cation and hydrogen carbonate dimer in a 1:1 molar ratio,47,48 we decided to employ the urea/thiourea molecule as a “pseudo-C3symmetric”49 molecular component to match the hydrogenbonding sites of the isocyanurate monoanion for the generation of new types of rosette tapes or layers. In the present work, we report the preparation and X-ray structural characterization of a series of seven new inclusion compounds generated from the isocyanurate monoanion and urea/thiourea molecule as complementary components of new anionic host lattices with peralkylated ammonium ions of different sizes as cationic guests: (CH3)4N+C3H2N3O3−· 3(NH2)2CS·H2O (1), (CH3)4N+C3H2N3O3−·(NH2)2CS (2), (C 2 H 5 ) 4 N + C 3 H 2 N 3 O 3 − ·(NH 2 ) 2 CS (3), (n-C 3 H 7 ) 4 N + C3H2N3O3−·(NH2)2CS·H2O (4), 3[(n-C4H9)4N+C3H2N3O3−]·5(NH2)2CS·3H2O (5), (C2H5)4N+C3H2N3O3−·(NH2)2CO (6), and (n-C3H7)4N+C3H2N3O3−·2(NH2)2CO·H2O (7)

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hydroxide solution. About 3 mL of deionized water was introduced, and different amounts of thiourea were added to the solution for each experiment: four molar equivalents for (1), and three molar equivalents for (3), (4), and (5) each. The solutions were evaporated at room temperature in a desiccator charged with anhydrous calcium chloride. Deposition of colorless block-like crystals occurred in nearly quantitative yield over a period of 2−3 weeks. Special Procedure for the Preparation of Hygroscopic Channel-Type Inclusion Complex (2). To a 100 mL roundbottomed flask, cyanuric acid (0.3000 g) was mixed with tetramethylammonium hydroxide (25 wt %, 0.8448 g). The mixture was stirred for 10 min, and 1 mL of water was then added. The solution turned cloudy, and a few drops of hydroxide were introduced. After being stirred for 5 min, the solution was heated with stirring. Absolute methanol (60 mL) was next poured into the flask, and the solution was evaporated by a rotary evaporator to give a white solid. This procedure was repeated five times to ensure complete removal of water. Afterward, thiourea (0.1770 g) was mixed with the white solid, and sufficient absolute methanol was added to redissolve the mixed solid upon heating. The solution was transferred to a 50 mL beaker, which was then covered by a piece of parafilm with a punctured hole. The solution was allowed to stand at ambient temperature, and small rectangular blocks of crystalline complex (2) were deposited after 3 days. It is noteworthy that the white solid was not very soluble in cold methanol, but it readily dissolved in boiling methanol. A significant amount of white powder would be deposited at the bottom of the beaker after cooling of the solution when insufficient methanol was added. If the powder was filtered and the filtrate subjected to further evaporation, the stable cage-type inclusion complex (1) in the form of small rectangular prisms would be obtained after 1 week. (CH3)4N+C3H2N3O3− ·3(NH2)2CS·H2O (1). Mp 179.5−182.2 °C. Anal. Calcd for C10H28N10O4S3 (448.60): C, 26.77; H, 6.29; N, 31.22; S, 21.44. Found: C, 26.73; H, 6.32; N, 30.98; S, 21.61. (CH3)4N+C3H2N3O3−·(NH2)2CS (2). Mp 196.8−201.3 °C. Anal. Calcd for C8H18N6O3S (278.34): C, 34.52; H, 6.52; N, 30.19; S, 11.52. Found: C, 34.48; H, 6.58; N, 30.12; S, 11.67. (C2H5)4N+C3H2N3O3−·(NH2)2CS (3). Mp 215.8−222.6 °C. Anal. Calcd for C12H26N6O3S (334.45): C, 43.10; H, 7.84; N, 25.13; S, 9.59. Found: C, 43.09; H, 7.93; N, 25.08; S, 9.74. (n-C3H7)4N+C3H2N3O3−· (NH2)2CS·H2O (4). Mp 222.8−224.4 °C. Anal. Calcd for C16H36N6O4S (408.57): C, 47.04; H, 8.88; N, 20.57; S, 7.85. Found: C, 47.05; H, 8.92; N, 20.51; S, 7.99. 3[(n-C4H9)4N+C3H2N3O3−]·5(NH2)2CS·3H2O (5). Mp 171.9− 174.8 °C. Anal. Calcd for C62H140N22O12S5 (1546.26): C, 48.16; H, 9.13; N, 19.93; S, 10.37. Found: C, 48.12; H, 9.16; N, 19.89; S, 10.49. For (6) and (7), similar procedures as those for (1)−(5) were empolyed, except that different amounts of urea was added in each case: four molar equivalents for (6) and two molar equivalents for (7). Colorless crystals in the form of large blocks were obtained in nearly quantitative yield after about one month. As compound (7) is hygroscopic, a selected crystal specimen was sealed in a Lindemann glass capillary for X-ray intensity data collection. (C2H5)4N+C3H2N3O3−·(NH2)2CO (6). Mp 162.3−165.1 °C. Anal. Calcd for C12H26N6O4 (318.39): C, 45.27; H, 8.23; N, 26.40. Found: C, 45.25; H, 8.26; N, 26.39.

EXPERIMENTAL SECTION

Materials and Physical Measurements. Commercially available cyanuric acid, thiourea, urea, and aqueous solutions of (CH4)4N+OH−, (C2H5)4N+OH−, (n-C3H7)4N+OH−, and (n-C4H9)4N+OH− purchased from Sigma-Aldrich were used as received without further purification. Elemental analysis for C, H, N, and S were performed on an Elementar Vario EL elemental analyzer. Melting points (uncorrected) were measured on an IA9100 electrothermal digital melting point apparatus. IR spectra were recorded with KBr pellets on a Nicolet Impact 420 FT-IR spectrometer in the region of 4000−400 cm−1. Powder X-ray diffraction (PXRD) intensities for polycrystalline samples of (1)−(7) were measured at 293 K on Bruker D8 Advance diffractometer (CuKα, λ = 1.54056 Å) by scanning over the range of 5−60° with step of 0.2°/ s. Simulated powder XRD patterns of (1)−(7) were generated with Mercury program (Figures S1−S7 in Supporting Information). Synthesis of Crystalline Inclusion Complexes Containing Tetraalkylammonium Isocyanurate and Thiourea/Urea. General procedure for (1)−(5): Cyanuric acid was deprotonated by one molar equivalent of the corresponding aqueous tetraalkylammonium 760


a

C8H18N6O3S (CH3)4N+C3H2N3O3−· (NH2)2CS 278.34 monoclinic C2/c 24.931(6) 7.189(2) 19.741(4) 90 128.229(6) 90 2779.0(1) 8 1.330 1184 0.0729 1.099 0.0379 0.1060 0.0385 0.1067 0.362/−0.327 1444797

C10H28N10O4S3 (CH3)4N+C3H2N3O3−· 3(NH2)2CS·H2O 448.60 monoclinic P21/n

8.991(1) 17.149(2) 14.636 (2) 90 104.434(3) 90 2185.5(5) 4 1.363 952 0.0323 1.024 0.0421 0.1040 0.0734 0.1230 0.373/−0.272 1444796

empirical formula molecular formula

761

R1 = Σ∥F0| − |Fc∥/Σ|F0|. bwR = [Σ[w(F02 − Fc2)2]/Σw(F02)2]1/2.

molecular weight crystal system space group Flack parameter a/Å b/Å c/Å α/° β /° γ /° V/Å3 Z Dc (g·cm−3) F(000) Rint GOF R1a (I > 2σ) wR2b (I > 2σ) R1a (all data) wR2b (all data) max/min (e·Å−3) CCDC number

(2)

(1)

crystal data

13.101(1) 8.9637(7) 16.176 (1) 90 96.492(2) 90 1887.5(3) 4 1.177 720 0.0263 0.908 0.0541 0.1361 0.0816 0.1512 0.394/−0.348 1444798

C12H26N6O3S (C2H5)4N+C3H2N3O3−· (NH2)2CS 334.45 monoclinic P21/n

(3)

Table 1. Crystallographic Data and Structure Refinement of Complexes (1)−(7)

9.8268(6) 16.552(1) 14.2860(9) 90 94.201(2) 90 2317.4(3) 4 1.171 888 0.0253 0.938 0.0486 0.1437 0.0813 0.1624 0.804/−0.159 1444799

C16H36N6O4S (n-C3H7)4N+C3H2N3O3−· (NH2)2CS·H2O 408.57 monoclinic P21/n

(4) C62H140N22O12S5 3[(n-C4H9)4N+C3H2N3O3−]· 5(NH2)2CS·3(H2O) 1546.26 triclinic P1 −0.02(6) 8.314(3) 9.165 (1) 29.019(3) 89.637(8) 83.22(1) 88.95(1) 2195.4(8) 1 1.170 842 0.0000 1.038 0.0472 0.0888 0.0824 0.1014 0.155/−0.202 1444800

(5)

8.7105(8) 13.374 (1) 15.154 (1) 90 90.705(2) 90 1765.3(3) 4 1.198 688 0.0296 1.016 0.0521 0.1530 0.0964 0.1818 0.180/−0.193 1444801

C12H26N6O4 (C2H5)4N+C3H2N3O3−· (NH2)2CO 318.39 monoclinic P21/n

(6)

17.394(3) 8.963(2) 17.768(4) 90 117.14(3) 90 2465.1(9) 4 1.219 984 0.0285 0.982 0.0448 0.1218 0.1193 0.1433 0.169/−0.158 1444802

C17 H40 N8 O6 (n-C3H7)4N+C3H2N3O3−· 2(NH2)2CO·H2O 452.57 monoclinic P21/n

(7)

Crystal Growth & Design Article



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(n-C3H7)4N+C3H2N3O3−·2(NH2)2CO·H2O (7). Mp 186.4−188.2 °C. Anal. Calcd for C17H40N8O6 (452.57): C, 45.27; H, 9.50; N, 26.39. Found: C, 45.24; H, 9.54; N, 26.35. X-ray Crystallography. Intensity data of complexes (1)−(7) were collected on a Bruker SMART 1000 CCD system with MoKα radiation (λ = 0.71073 Å) from a sealed-tube generator at 293 K. Data collection and reduction were performed using SMART and SAINT software,50 and empirical absorption corrections were applied.51 All the structures were solved by direct methods with SHELXS-97 program, and all nonhydrogen atoms were subjected to anisotropic refinement by fullmatrix least-squares on F2 using the SHELXL-97 program.52 All the hydrogen atoms were included in the structure factor calculation at idealized positions using a riding model and refined isotropically. The hydrogen atoms of the solvent water molecules were located from difference Fourier maps and then restrained at fixed positions and refined isotropically. The crystallographic data and geometry of the hydrogen bonds for complexes (1)−(7) are listed in Tables 1 and S1− S7. Crystallographic data for the structures reported in this article have been deposited in Supporting Information.

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RESULTS AND DISCUSSION Crystal Structure of (CH3)4N+C3H2N3O3−·3(NH2)2CS· H2O (1). Complex (1) is a cage-type inclusion compound.

Figure 2. Hydrogen-bonding scheme of the second structural component of the hydrogen-bonded cage in (1). The cyclic parallelogram-like (thiourea S2-water)2 tetrameric units are connected together by the third independent thiourea S3 and its symmetryrelated partner to form a large rectangular grid, which serves as a side wall orientated parallel to the (1 0 1)̅ family of planes. Dashed lines represent hydrogen bonds. Symmetry transformations: a (1.5 − x, 0.5 + y, 0.5 − z); b (2 − x, 1 − y, 1 − z); c (0.5 + x, 0.5 − y, 0.5 + z).

Figure 1. Projection diagram along the a-axis showing a platform of the hydrogen-bonded grid in (1). One of the zigzag ribbons composed of the dimers of isocyanurate ions and thiourea molecules is highlighted with orange bonds. Dashed lines represent hydrogen bonds. Symmetry transformations: a (1 − x, 1 − y, 1 − z); b (1 − x, −y, 1 − z); c (0.5 + x, 0.5 − y, 0.5 + z).

The hydrogen-bonded cage can be regarded as a combination of two structural components: (i) a platform or ceiling constructed with one independent thiourea molecule (designated S1 for convenience) and the isocyanurate ion; (ii) a grid of side-walls constructed with the remaining two independent thiourea molecules S2, S3, and water molecule O1w. In the cage-type host lattice of (1), two centrosymmetrically related isocyanurate ions are joined together by a pair of N− H···OC hydrogen bonds to form a ring motif A, N2 = R22(8). Another pair of isocyanurate ions related by simple translation along the b-axis are bridged by a thiourea dimer via a pair of N−H···S and N−H···OC hydrogen bonds [B, N2 = R22(8)] to form a zigzag ribbon running along the [0 1 0] direction (Figure 1). Adjacent ribbons arranged side-by-side are further

Figure 3. Perspective view of a rectangular hydrogen-bonded cage in (1) viewed along the a-axis, which accommodates two (CH3)4N+ cations. The dimensions of the hydrogen-bonded cage are about 9 × 9 × 14 Å3.

cross-linked by N−H···N− and N−H···OC hydrogen bonds [C, N2 = R22(8)] to generate an essentially planar host layer, which acts as a large platform or ceiling of the hydrogenbonded cage (Figure 2). This host layer can be considered as a new type of anionic rosette layer with a distorted quasihexagonal void [D, N6 = R64(16)] formed by three thiourea molecules and three isocyanurate ions. The second independent thiourea molecule S2 and its centrosymmetrically related partner are bridged by a pair of 762



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S hydrogen bonds [E, N4 = R44(12)], and the third independent thiourea molecules S3 are connected to the (thiourea-water)2 tetrameric units in a typical shoulder-toshoulder manner [F, N2 = R22(8)] to generate a large rectangular grid [G, N12 = R126(32)] (Figure 2). The grid is further joined to the platform via N−Hanti···OC and N− Hanti···N− hydrogen bonds (Figure 3) to produce a large rectangular box which can encapsulate two (CH3)4N+ cations (Scheme 2). Detailed hydrogen-bonding geometries are listed in Table S1. Crystal Structure of (CH3)4N+C3H2N3O3−·(NH2)2CS (2). The channel-type host lattice of complex (2) is constructed with one crystallographically independent isocyanurate ion and one thiourea molecule. Two isocyanurate ions related by an inversion center are joined together by a pair of strong N−H··· OC hydrogen bonds in a complementary manner [A, N2 = R22(8)] (Figure 4a). Neighboring isocyanurate ions related by an inversion center are connected to this isocyanurate dimer via a pair of N−H···OC hydrogen bonds [B, N2 = R22(8)] to form a zigzag chain extending along the [101] direction. The neighboring zigzag isocyanurate chains related by the c-glide plane are cross-linked at each of the turning points by a pair of thiourea molecules via a N−H···OC and a pair of strong N−

Scheme 2. Schematic Diagram Showing a Rectangular Grid in the Hydrogen-Bonded Cage-Type Structure of (1)a

a

Two (CH3)4N+ cations represented by large spheres can be accommodated in each cage.

water molecules to form a parallelogram-like (thiourea-water)2 tetrameric unit via two pairs of N6−Hsyn···O1w and O1w−H···

Figure 4. (a) Upper part: projection diagram viewed along the b-axis showing the hydrogen-bonding interactions in the cross-sectional regions of a host channel of (2). The thiourea linkers highlighted by green bonds and the zigzag isocyanurate chains that lie at y = 1/4 and 3/4 are distinguished by red and orange bonds, respectively. (b) Lower part: the host channel viewed parallel to the [1 0 1] direction. Another zigzag isocyanurate chain and thiourea linkers lying at y = 5/4 are highlighted by gray bonds. Symmetry transformations: a (1 − x, y, 0.5 − z); b (0.5 + x, 0.5 − y, 0.5 + z); c (0.5 − x, 0.5 + y, 0.5 − z). 763



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independent isocyanurate ion and its centrosymmetrically related partner are joined together by a pair of homomeric N−H···OC hydrogen bonds [A, N2 = R22(8)]. Two inversion-related thiourea molecules are connected together by a pair of strong N−Hsyn···SC hydrogen bonds in a typical shoulder-to-shoulder fashion [B, N2 = R22(8)]. These two kinds of dimers are alternately arranged and joined together via pairs of strong N−Hanti···N− and N−Hanti···OC hydrogen bonds [C, N2 = R22(8)] to form a zigzag thiourea-isocyanurate tape running parallel to the [0 1 1] direction. Adjacent thiourea-isocyanurate tapes related by a simple translation along the a-axis are interlinked together via pairs of N−Hsyn···O and N−H···S hydrogen bonds [D, N2 = R22(8)] to generate an essentially planar layer exhibiting two new types of supramolecular rosette motifs with large voids [E, N6 = R66 (20) and F, N6 = R64 (16)] (Figure 7). The rosette layers corresponds to the (1/2 0 0) family of planes, and the wellordered (C2H5)4N+ cations are sandwiched between the host layers with an interlayer spacing of about 6.5 Å (Figure 8). Detailed hydrogen-bonding geometries are listed in Table S3. Crystal structure of (n-C3H7)4N+C3H2N3O3−·(NH2)2CS· H2O (4). The host layer of (4) is constructed by the crosslinkage of isocyanurate−thiourea−water ribbons (Figure 9). A pair of independent isocyanurate ion and thiourea molecule are alternately arranged and connected together by pairs of N−H··· OC and N−H···N− hydrogen bonds in a complementary manner to form a zigzag isocyanurate−thiourea ribbon along the b-axis with ring motifs A, N2 = R22(8) and B, N2 = R22(8), which is further consolidated by water molecules of type O1w via pairs of strong O−H···OC hydrogen bonds [C, N4 = R43(10)]. Adjacent antiparallel isocyanurate−thiourea ribbons are cross-linked by pairs of strong N1−H···OC [D, N2 = R22(8)] and N4−H···O1w [E, N4 = R43(10) and F, N6 = R66(20)] to form a host layer. The well-ordered (n-C3H7)4N+ cations are sandwiched between host layers that matches the (1 0 1̅) family of planes (Figure 10). Detailed hydrogen-bonding geometries are listed in Table S4. Crystal Structure of 3[(n-C 4 H 9 ) 4 N + C 3 H 2 N 3 O 3 − ]·5(NH2)2CS·3H2O (5). In the crystal structure of (5), the asymmetric unit consists of five thiourea molecules, three isocyanurate ions, and three water molecules. The anionic host layer can be considered as a combination of three structural components, namely, two types of ribbons and a dimeric linker (Figure 11). Two independent thiourea molecules are joined together by a pair of strong N−Hsyn···S hydrogen bonds to form a dimer with motif A, N2 = R22(8). Adjacent thiourea dimers related by simple translation along the b-axis are alternately bridged by two independent isocyanurate ions via pairs of strong N− Hanti···OC, N−Hanti···N−, and N−Hsyn···S hydrogen bonds in a complementary manner [B and C, N2 = R22(8); D and E, N2 = R22(8)] to form another new type of slightly puckered rosette tape with a large void F, N6 = R64(16) running along the b-axis. The rosette tape is further consolidated by water molecules of type O1w via pairs of strong O1w−H···OC hydrogen bonds between two isocyanurate ions [G, N4 = R43(10)]. The third isocyanurate ion is joined to the third independent thiourea molecule via the second bridging water molecule by N8−H···O2w, O2w−H···SC, and N15−Hsyn···OC hydrogen bonds [H, N3 = R33(10)], and to the fourth independent thiourea molecule via a pair of heteromeric N7−H···SC and N16−Hsyn···OC hydrogen bonds [I, N2 = R22(8)] to yield a

Figure 5. Detailed hydrogen-bonding interactions between the thiourea linkers and the isocyanurate chains in (2). Three thiourea molecules and three isocyanurate ions are interlocked together by pairs of strong N−H···OC and N−H···N− hydrogen bonds. The hydrogen bond motifs and atom labeling scheme are identical to those used in Figure 4. Symmetry transformation: c (0.5 − x, 0.5 + y, 0.5 − z); d (0.5 − x, − 0.5 + y, 0.5 − z).

H···N− hydrogen bonds [C, N2 = R22(8) and D, N4 = R43(12)]. Adjacent thiourea molecules inter-related by a 2-fold screw axis are oppositely oriented to each other, and this pair of unconnected linkers lies approximately at the same level as, and is oriented nearly perpendicular to, the isocyanurate chains. Positioning of such thiourea linkers at the turning points of the isocyanurate zigzag chains facilitates their cross-linkage to generate a host layer with large voids E, N8 = R86(28) (Figure 4a). Note that each of the amido groups of thiourea can form two distinct types of hydrogen bonds: (i) N4−Hanti···OC and N4−Hsyn···OC; (ii) N5−Hanti···N− and N5−Hsyn···N−. At each turning point, there are three N4−H···OC and three N5−H···N− hydrogen bonds between two adjacent zigzag ribbons (Figure 4b and Figure 5). Neighboring layers are stacking over each other along the baxis and interlinked by pairs of strong N−H···OC and N− H···N− hydrogen bonds to form an intersecting channel-type host framework which can accommodate two separate columns of well-ordered (CH3)4N+ cations (Figure 6a,b). Besides the strong charge-assisted hydrogen-bonding interactions, an extensive network of weak C−H···OC interactions between the (CH3)4N+ cation and the amido oxygen of isocyanurate ion, C8−H8b···O2 and C8−H8c···O3 further enhances the stability of the inclusion complex. Detailed hydrogen-bonding geometries are listed in Table S2. Interestingly, the thiourea sulfur atom does not participate in the construction of the host lattice, which is not usually observed among the known inclusion compounds of thiourea. A similar example can be found in the inclusion compound of 5-nitrobarbiturate, 2[(CH 3 ) 4 N + ]·2[(C 4 H 2 N 3 O 5 ) − ]· (NH2)2CS.15 Crystal Structure of (C2H5)4N+C3H2O3−·(NH2)2CS (3). The layer-type anionic host lattice of (3) is constructed with an independent isocyanurate ion and one thiourea molecule that fully utilize their hydrogen-bonding sites (Figure 7). The 764



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Figure 6. (a) Perspective view of the crystal structure of (CH3)4N+C3H2N3O3−·(NH2)2CS (2) along the b-axis. A small channel system is formed by the quasi-hexagonal rings between the host layers. Two columns of well-ordered (CH3)4N+ cations (represented by large spheres for clarity) are accommodated in each channel. The cross-sectional area of the channel is about 7.6 Å × 12.2 Å. (b) Perspective view of the large rectangular channel system in the crystal structure of (CH3)4N+C3H2N3O3−·(NH2)2CS (2) along the [1 0 1] direction. The cross-sectional area of the channel is about 7.2 Å × 8.5 Å.

“Λ”-shaped structural unit. Adjacent “Λ”-shaped structural units related by the b-translation are further interlinked together via N16−Hanti···N−, N14−Hanti···OC, N15−Hanti···OC and N17−Hanti···OC hydrogen bonds [J, N2 = R21(6); K, N2 = R22(8); L, N2 = R43(10)] to generate a wide composite ribbon with “butterfly-like” hydrogen-bonded motifs. The composite ribbon is interlinked to the neighboring rosette tape via O2w−H···O1w, N5−H···SC [M, N4 = R43(10)], and N14−Hsyn···O6 [N, N4 = R22(8)] hydrogen bonds. Another side of the composite ribbon is cross-linked to the rosette tape by thiourea-water linkers [O, N2 = R21(6)], which is composed of the fifth independent thiourea and water molecule of type O3w, via N2−H···SC, N18−Hsyn···OC [P, N2 = R22(8)], O3w−H···OC [Q, N5 = R54(12)], N17− Hsyn···SC, N19−Hsyn···OC [R, N3 = R32(8)], O3w−H··· SC [S, N4 = R43(10) and T, N4 = R43(12)] to produce a

slightly wavy host layer (Figure 12). The well-ordered (nC4H9)4N+ cations are sandwiched between these wavy layers with an interlayer spacing of about 8.3 Å. The crystal structure is further consolidated by weak C−H···O interactions between the α-methylene hydrogens of (n-C4H9)4N+ cations and the amido carbonyl oxygen atoms of isocyanurate ions. Detailed hydrogen-bonding geometries are listed in Table S5. Crystal Structure of (C2H5)4N+(C3H2N3O3)−·(NH2)2CO (6). The independent isocyanurate ion and thiourea molecule make full use of their hydrogen-bonding donor and acceptor sites to generate the anionic host layer of (6) (Figure 13). Two inversion-related isocyanurates are joined together by a pair of strong N−H···OC hydrogen bonds to form a dimer with a ring motif A, N 2 = R 2 2 (8). In a similar manner, a centrosymmetric urea dimer is held by a pair of strong N− H···OC hydrogen bonds to yield ring motif B, N2 = R22(8). 765



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Figure 7. Projection diagram viewed along the a-axis showing the hydrogen-bonding interactions in the host layer of (C2H5)4N+C3H2O3−·(NH2)2CS (3), which exhibits a rosette motif. Symmetry transformations: a (1−x, 2−y, 2−z); b (1−x, 1−y, 1−z); c (x, − 1 + y, z).

Figure 8. A portion of crystal structure of (3) viewed along the b-axis. The well-ordered (C2H5)4N+ cations are sandwiched between the layers of the anionic host lattices. The hydrogen atoms on (C2H5)4N+ cations are omitted for clarity, and the interlayer separation is about 6.5 Å.

bonds to form cyclic (isocyanurate-urea-water)2 hexamer containing motifs A, N3 = R33(10); B, N2 = R22(8); C, N4 = R 4 2 (8). Another independent urea molecule forms a centrosymmetric dimer in motif D, N2 = R22(8). Adjacent (isocyanurate−urea−water)2 hexamers are alternately bridged by the urea dimers via pairs of strong N−H···OC hydrogen bonds in motif E, N2 = R22(8) to yield a puckered ribbon running parallel to the [1 1̅ 0] direction. This ribbon together with its translational equivalents along the c-axis constitute the side-walls of the [1 0 1] channel system (Figure 16). Neighboring puckered ribbons related by an inversion center at (1/2, 0, 1) and similar sets of isocyanurate-urea-water ribbons running parallel to the [1 1 0] direction are alternately arranged and cross-linked together by pairs of N−H···O [F, N5 = R54(16)] and O−H···O hydrogen bonds via bridging water molecules [G, N3 = R33(10)] to generate a three-dimensional host framework with intersecting channel systems running parallel to the [0 0 1], [1 0 1], [1 1 0], and [1 1̅ 0] directions with distinct sizes and shapes (see Figures S8−S11 in Supporting Information). The well-ordered (n-C3H7)4N+ cations are enclosed in the channel and arranged in a zigzag fashion. Detailed hydrogen-bonding geometries are listed in Table S7.

The isocyanurate and urea dimers alternately arranged along the [1 0 1̅] direction are connected by pairs of strong N−H··· OC and N−H···N− hydrogen bonds with motif C, N2 = R22(8) to produce a zigzag ribbon. Neighboring ribbons related by simple translation along the a-axis are further cross-linked by pairs of strong N−H···OC hydrogen bonds with an additional ring motif D, N2 = R22(8) to generate an essentially planar host layer exhibiting two different types of supramolecular rosette motifs with large voids [E, N6 = R66(20) and F, N6 = R64(16)]. The well-ordered (C2H5)4N+cations are alternately arranged along the c-axis and sandwiched between the planar hydrogenbonded host layers with an interlayer spacing of about 6.7 Å (Figure 14). Detailed hydrogen-bonding geometries are listed in Table S6. Crystal Structure of (n-C 3 H 9 ) 4 N + (C 3 H 2 N 3 O 3 ) − ·2(NH2)2CO·H2O (7). The host lattice of (7) contains several intersecting channel systems which are constructed by the cross-linkage of two sets of isocyanurate-urea-water ribbons, as shown in Figure 15. Centrosymmetrically related pairs of isocyanurate ions, urea molecules, and bridging water molecules are held by a system of strong N1−H···O1w, O1w−H···O4a, N5a−Hsyn···O1, N5−Hanti···O1, and N4−Hanti···N− hydrogen 766



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Figure 9. Projection diagram showing the hydrogen-bonding interactions in the anionic host layer of (n-C3H7)4N+C3H2N3O3−·(NH2)2CS·H2O (4). Broken lines represent hydrogen bonds, and atom types are differentiated by size and color. A zigzag isocyanurate−thiourea ribbon is highlighted with orange bond color. The host layer matches the (1 0 1)̅ family of planes. Symmetry transformations: a (0.5 − x, − 0.5 + y, 0.5 − z); b (0.5 − x, 0.5 + y, 0.5 − z); c (1 − x, 1 − y, 1 − z).

Figure 10. Projection diagram viewed along the b-axis showing a portion of the crystal structure of (4). The well-ordered (n-C3H7)4N+ cations represented by the large blue spheres are sandwiched between the anionic host layers. The host layers correspond to the (1 0 1)̅ family of planes with an interlayer separation of about 8.9 Å.

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DISCUSSION

framework (Figure 4). It would be interesting to see if similar structural changes would occur when water molecules are removed from (n-C3H7)4N+C3H2N3O3−·(NH2)2CS·H2O (4) and 3[(n-C4H9)4N+C3H2N3O3−]·5(NH2)2CS·3H2O (5). Unfortunately, the corresponding organic salts are sparingly soluble in absolute methanol, and only a white powder could be obtained after several days of slow evaporation in air. The water molecules in complexes (4), (5) and (nC3H7)4N+C3H2N3O3−·2(NH2)2CO·H2O (7) also play important roles in the formation of the host frameworks. In both layer-type complexes (4) and (5), the water molecules derived from O1w consolidate the isocyanurate−thiourea rosette tape by bridging two neighboring isocyanurate ions via O−H···O

Structural Types of Thiourea/Urea-isocyanurate Host Lattices and Supramolecular Rosette Motifs. The water molecule in (CH3)4N+C3H2N3O3−·3(NH2)2CS·H2O (1) serves as a key structural component in forming the hydrogen-bonded molecular cage that accommodates a pair of (CH3)4N+ ions (Figure 3). However, when the preparation is carried out in absolute methanol after exhaustive removal of water from the solution, (CH3)4N+C3H2N3O3−·(NH2)2CS (2) is obtained. Without the participation of water molecules in host lattice construction, the molar thiourea to isocyanurate ratio decreases to 1:1, yielding a completely different channel-type host 767



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Figure 11. Projection diagram along the a-axis showing the hydrogen-bonding interactions in the host layer of 3[(n-C4H9)4N+(C3H2N3O3)−]· 5(NH2)2CS·3H2O (5). Symmetry transformations: a (x, 1 + y, z); b (x, y, z + 1); c (x, y − 1, z + 1).

Figure 12. Packing diagram viewed along the b-axis showing a portion of the crystal of 3[(n-C4H9)4N+C3H2N3O3−]·5(NH2)2CS·3H2O (5). Pseudospherical and well-ordered (n-C4H9)4N+ cations are sandwiched between the layers with an interlayer separation of about 8.3 Å. The hydrogen atoms of (n-C4H7)4N+ cations are not shown for clarity.

C hydrogen bonds and provide hydrogen-bond accepting sites to further link up adjacent composite ribbons. In complex (5), the water molecules derived from O2w bridge between the isocyanurate ion and thiourea molecule, leaving one hydrogenbond donor site to bind water molecule O1w in the neighboring rosette ribbon. In addition, the water molecules derived from O3w sit under the thiourea molecules to form “parachute-like” linkers, each connecting adjacent composite ribbons and rosette tapes via pairs of strong N−H···OC and O−H···SC hydrogen bonds (Figure 11). The water molecules in complex (7) not only consolidate the isocyanurate−urea ribbon, but also facilitate the cross-linkage of differently orientated isocyanurate−urea ribbons, as one O−

H group of every water molecule points outward from the essentially planar ribbon. As shown in Table 2, the isocyanurate ion having C2v molecular symmetry can form different numbers of hydrogen bonds with its neighboring chemical species in the seven inclusion complexes (see Figures S12−S18 in Supporting Information). The N−H···OC type interaction is predominant, and the charged-assisted N−H···N− hydrogen-bonding interaction makes an important contribution to the selfassembly of these inclusion complexes. Notably, suitable selection of peralkylated ammonium cations serving as guest templates can have a significant effect on inclusion topology. As cationic size increases, the anionic 768



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Figure 13. Projection diagram viewed along the b-axis showing the hydrogen-bonding interactions in the anionic host layer of (C2H5)4N+(C3H2N3O3)−·(NH2)2CO (6). Broken lines represent hydrogen bonds, and atom types are distinguished by size and color. Symmetry transformations: a (1 + x, y, z); b (1 − x, 1 − y, 1 − z); c (−x, 1 − y, 2 − z).

Figure 14. Perspective view along the c-axis showing a portion of the crystal structure of (C2H5)4N+(C3H2N3O3)−·(NH2)2CO (6). The bulky (C2H5)4N+ cations are sandwiched just above and below the large voids in the host layers, and the weak methylene C−H···OC hydrogen bonds between (C2H5)4N+ cations and isocyanurate ions are also illustrated. The interlayer distance is about 6.7 Å.

layers with non-C3-symmetric anions has been achieved by employing the planar dithiosquarate dianion and the nonplanar 1,1′-biphenyl-2,2′,6,6′-tetracarboxylate dianion.17 The above rosette ribbons or layers involve the use of the guanidinium cation, which is able to direct neighboring counteranions to be arranged around it with appropriate C3 symmetry via hydrogen bonding interactions. Our next challenge is to construct the rosette network without using any C3-symmetric molecular components. In complex (5) a new type of supramolecular rosette ribbon is formed by cross-linking two pairs of thiourea dimers and two isocyanurate ions (Figure 17) as part of the host layer. The size of the new rosette motif is about 12 Å × 14 Å, which is slightly larger than that formed by the bicarbonate and guanidinium ions (9 Å × 11 Å). It should be noted that the bicarbonateguanidinium rosette ribbon is constructed from two independent bicarbonate ions and two independent guanidinium ions,

host structure changes from cage- through channel- to layertype (Table 3). The supramolecular rosette motifs assembled with isocyanurate and thiourea/urea, as found in the present study, are compared in Figure 16. Two examples of a supramolecular fused-rosette ribbon assembled from bicarbonate dimer and guanidinium ion were reported by our research group in 2000.47,48 Using C3symmetric guanidinium and trimesate ions, an essentially planar rosette layer bearing a monocyclic water hexamer in a central cavity of the layer was obtained, whereas an unusual sinusoidal rosette layer built of guanidinium and carbonate ions was successfully prepared in the presence of oxalate ion and extra guanidinium ion as supporting agents.53 Later, a wavy guanidinium-carbonate rosette layer was induced to adopt a nearly planar configuration using 1-H-imidazole-4,5-dicarboxylate as an auxiliary template and spacer. More recently, a significant breakthrough in the construction of two rosette 769



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Figure 15. Perspective diagram showing a cross-sectional layer of the anionic host framework with intersecting channels in (nC3H9)4N+(C3H2N3O3)−·2(NH2)2CO·H2O (7). Two types of ribbons with different orientations are drawn in distinct bond colors, and their directions are further indicated by the arrows. Symmetry transformations: a (1 − x, −y, 1 − z); b (−x, 1 − y, 1 − z); c (0.5 − x, 0.5 + y, 1.5 − z); d (0.5 − x, −0.5 + y, 1.5 − z); e (0.5 + x, 0.5 − y, 0.5 + z).

Figure 16. Comparison of different supramolecular rosette motifs observed in the present work: (a) in complex (1), (b) in complex (3), (c) in complex (3) and (5), (d) and (e) in complex (6).

IR Spectra of Complexes (1)−(7). In crystalline complexes (1)−(7), the N−H stretching band at 3180−3140 cm−1 indicates the presence of the hydrogen-bonded amide groups. Strong CO stretching vibrations appear at 1760−1720 cm−1 and 3430−3350 cm−1 for the secondary amide groups in the isocyanurate monoanion. The N−H bending mode is also observed at 1650−1620 cm−1, while urea and thiourea exhibit CO stretching vibration at 1690−1650 cm−1.

and hence the ribbon is electrically neutral. However, the new thiourea−isocyanurate rosette ribbon in (5) is anionic, being generated by two independent thiourea molecules and two independent isocyanurate ions. In addition, essentially planar host layers (Figure 7 and Figure 13) exhibiting the fused-rosette pattern are observed in thiourea complex (3) and urea complex (6). The anion and the cationic guest template are identical in the both complexes, but the same type of rosette layer is formed despite the fact that thiourea forms a much longer N−H···SC acceptor hydrogen bond. Thus, this pair of complexes provides another interesting example of isostructural exchange between equivalent building blocks in supramolecular architecture.46,54−56

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CONCLUSION The present work has demonstrated that when the D3h molecular symmetry of isocyanuric acid is lowered to C2v after mono-deprotonation, it remains as a very versatile 770



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Table 2. Hydrogen-Bonding Interactions between Isocyanurate Ion and Its Neighboring Chemical Speciesa inclusion complex

no. of N−H···OC

no. of N−H···SC

no. of N−H···N−

no. of C−H···OC

no. of O−H···OC

(1) (2) (3) (4) (5)

7 6 4 4 3 3 6 5 6

1 0 1 1 2 2 1 0 0

2 2 1 1 1 1 1 1 1

0 2 0 1 0 0 0 5 0

0 0 0 2 1 2 0 0 0

(6) (7) a

There are three independent isocyanurate ions in complex (5), and in both (5) and (7) there is one more N−H···O−H hydrogen bond between the isocyanurate ion and the water molecule.

bonding sites of the isocyanurate ion. Furthermore, it is found that the water molecule plays a crucial role in host lattice construction, as found in the pair of complexes (1) and (2), which exhibit completely different and unusal crystal structures even though they both contain the same cationic (CH3)4N+ guest template.

Table 3. Structural Types of Inclusion Complexes Reported in This Paper inclusion complex

guest template

host lattice

rosette pattern

(1) (2) (3) (4) (5) (6) (7)

(CH3)4N+ (CH3)4N+ (C2H5)4N+ (n-C3H7)4N+ (n-C4H9)4N+ (C2H5)4N+ (n-C3H7)4N+

cage-type channel-type layer-type layer-type layer-type layer-type channel-type

rosette layer no rosette motif rosette layer no rosette motif rosette tape rosette layer no rosette motif

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.5b01350. IR data, experimental and simulated powder X-ray diffraction patterns of complexes (1)−(7). Geometry of the hydrogen bonds, supplementary figures for complex (7), comparison of the bond lengths and bond angles of isocyanurate ions, the geometries of isocyanurate ions (without disorder or coordinating with metal ion)

building block for the construction of hydrogen-bonded rosette-type supramolecular architectures. New types of host networks exhibiting a variety of rosette motifs can be achieved provided that an appropiately chosen peralkylated ammonium guest template is employed, and suitable molecular components are also present to match with the donor/acceptor hydrogen-

Figure 17. Dimensions of two types of linear fused-rosette ribbons: (left) assembled from thiourea dimer and isocyanurate ion in 1:1 molar ratio (present work); (right) assembled from the HCO3− dimer and guanidinium ion in a 1:1 molar ratio.47 771



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retrieved from the Cambridge Crystallographic Database, representative linkage modes, hydrogen-bonding motifs, hydrogen-bonding interactions between the isocyanurate ion and its neighboring chemical species in complexes (1)−(7), and ORTEP drawings for complexes (1)−(7) (PDF) Accession Codes

CCDC 1444796−1444802 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: Int. code: +86 2084112469. Fax: +86 2084112245. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is supported by the Wei Lun Foundation, as well as the award of a postgraduate studentship to C.-W.Y. and a postdoctoral research fellowship to S.C.-K.H. by The Chinese University of Hong Kong. Funding provided by the Natural Science Foundation of China (No. 20503041) to C.-K.L. is gratefully acknowledged.

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REFERENCES

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(49) The term “pseudo-C3-symmetric” refers to a molecule having a trigonal-planar, non-H tetra-atomic skeleton with each terminal atom capable of functioning as a hydrogen-bonding donor or acceptor. (50) Bruker SMART 5.0 and SAINT 4.0 for Windows NT: Area Detector Control and Intergration Software; Bruker Analytical X-Ray Systems, Inc.: Madison, Wisconsin, USA, 1998. (51) Sheldrick, G. M. SADABS: Program for Empirical Absorption Correction of Area Detector Data; University of Göttingen: Göttingen, Germany, 1996. (52) Sheldrick, G. SHELXS-97, Program for Crystal Structure Solution, University of Göttingen, 1997; SHELXTL 6.10, Bruker Analytical Instrumentation, Madison, Wisconsin, USA, 2000. (53) Lam, C.-K.; Xue, F.; Zhang, J.-P.; Chen, X.-M.; Mak, T. C. W. J. Am. Chem. Soc. 2005, 127, 11536−11537. (54) Kálmán, A.; Párkányi, L. In Advances in Molecular Structure Research; Hargittai, M., Hargittai, I., Eds.; JAI Press: Stamford, CT, 1997; Vol. 3, pp 189−226. (55) Lam, C.-K.; Mak, T. C. W. Cryst. Eng. 2000, 3, 33−40. (56) Lam, C.-K.; Mak, T. C. W. Cryst. Eng. 2000, 3, 225−226.

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Hydrogen-Bonded Anionic Host Lattices Constructed with

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