Equivalence of NH - American Chemical Society

Equivalence of NH4+, NH2NH3+, and OHNH3+ in Directing the Noncentrosymmetric Diamondoid Network of O-H‚‚‚O- Hydrogen Bonds in Dihydrogen Cyclohexane Tricarboxylate

CRYSTAL GROWTH & DESIGN 2005 VOL. 5, NO. 3 1271-1281

Balakrishna R. Bhogala, Peddy Vishweshwar, and Ashwini Nangia* School of Chemistry, University of Hyderabad, Hyderabad 500 046, India Received January 25, 2005

W This paper contains enhanced objects available on the Internet at http://pubs.acs.org/crystal. ABSTRACT: The assembly of hexagonal and diamond network architectures from functionalized tectons of trigonal and tetrahedral symmetry, respectively, is an important activity in crystal engineering. We report a novel supramolecular transformation for the synthesis of diamond network structures from the trigonal molecule, 1,3cis,5-cis-cyclohexanetricarboxylic acid (H3CTA). Crystal structures of some salts of the trigonal anion, H2CTA-, with tetrahedral counterions is analyzed in H2CTA-‚NH4+ 1, H2CTA-‚MeNH3+ 2, H2CTA-‚EtNH3+ 3, H2CTA-‚NH2NH3+ 4, and H2CTA-‚OHNH3+ 5. The trigonal anion functions as a tetrahedral self-complementary node in the presence of NH4+ counterion (salt 1) via two COOH donors and COO- as a double hydrogen-bond acceptor. The triply interpenetrated diamondoid network of O-H‚‚‚O- hydrogen bonds in 1 is reproduced in isostructural 3D nets of 4 and 5 by substituting NH4+ by NH2NH3+ and OHNH3+ (Π ) 0.025, 0.027). The SHG activity of noncentrosymmetric diamondoid solids 1, 4, and 5 (space group Cc) is comparable to that of the nonlinear optical (NLO) material potassium dihydrogen phosphate (KDP) (0.3 × urea). However, salts 2 and 3 (space groups P21/c and P1 h ) have hexagonal and square grid layers of H2CTA- anions because the ammonium cation in these structures is devoid of the fourth strong hydrogen-bond donor group to extend crystal growth to the 3D diamond network. Thus, RNH3+ counterions may be used to control the anionic network of the H2CTA- molecule based on a tetrahedral node in 1, 4, and 5, a trigonal node in 2, and a square node in 3. The function of cyclohexane tricarboxylate as a four-connected node, shown for the first time in a trigonal molecule, is in contrast to the usual role of the trimesate anion as a three-connected node in molecular complexes. Introduction Molecular geometry, symmetry, and chemical functionality are important considerations in the design and predictable assembly of hydrogen-bond networks of increasing dimensionality. For example, benzoic acid, terephthalic acid, trimesic acid, and adamantane-1,3,5,7tetracarboxylic acid are prototype building blocks for the synthesis of discrete, one-, two-, and three-dimensional architectures in crystal engineering.1 Molecular tectonics2 is the science of modular, programmed build up from molecule to crystalsrod-type molecules form linear aggregates,3 chiral and C2-symmetry molecules lead to helical networks,4 C3/D3 symmetry molecules produce honeycomb grid or hexagonal layer structures,5 and Td/ S4 symmetry tectons self-assemble as adamantane networks.6 The ability to predict the network architecture from the shape and symmetry of the functionalized tecton is fundamental to crystal design (Scheme 1a). We7a,b have utilized these molecule-to-supermolecule relationships to build hexagonal network architectures from the trigonal molecule, 1,3-cis,5-cis-cyclohexanetricarboxylic acid (H3CTA).7 Ermer,1c Wuest,2a and others have constructed diamondoid architectures6,8 from tetrahedral tectons (e.g., methane, tetraphenylmethane, adamantane) with four identical functional groups (COOH, Br, CtCH, OH, B(OH)2, 2-pyridone, * To whom correspondence should be addressed. Fax: (+91) 40 23011338; e-mail: [email protected].

triamino-triazine) or two pairs of difunctional groups (COOH/COO-, I/NO2). Crystal engineering of 3D interpenetrated diamond networks continues to elicit interest because these functional solids are useful as secondorder nonlinear optical (NLO) materials.8d The trigonal molecule H3CTA with three hydrogenbond donor and acceptor groups becomes a self-complementary hydrogen-bonding tecton with two strong donors and two acceptors after deprotonation to the H2CTA- anion, dihydrogen 1,3-cis,5-cis-cyclohexane tricarboxylate (Scheme 1b).7b-d Even though the tricarboxylate anion has the potential to form strong OH‚‚‚O- hydrogen bonds to four different molecules, H2CTA- behaves as a three-connected T-node because the anions aggregate via COOH dimers in dipyridinium (Figure 1) and hexamethylenetetraammonium salts. The voids in these layered structures of H2CTA- anions are usually filled by counterion inclusion, whereas the neutral complexes close pack through interpenetration.7 Similarly, trimesate salts either form hexagonal porous channels for guest inclusion,5b,d or the anionic layers are intercalated by dialkyl/arylammonium cations in organic clay mimics.9 In this background, we have examined the self-assembly of ionic complexes between the trigonal H2CTA- anion and tetrahedral RNH3+ cations to find out if small counterions with divergent and directional hydrogen-bond donor groups can direct the arrangement of the tricarboxylate anion to four-connected nets, ideally in the adamantane framework.

10.1021/cg0500270 CCC: $30.25 © 2005 American Chemical Society Published on Web 03/03/2005

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Bhogala et al. Scheme 1a

a (a) Relationship between trigonal and tetrahedral molecular symmetry and hexagonal and diamond network structures, known in the molecular tectonics literature. (b) H3CTA molecule has three hydrogen-bond donors and three acceptor groups. After deprotonation, the H2CTA- anion has two donors (COOHs) and two acceptors (COO- oxygens). The anion functions as a T-node in bipyridinium salts. See Figure 1. (c) H2CTA- is shown to function as a four-connected tetrahedral tecton in ammonium salts.

While implementing such tecton-to-network strategies, one should be aware that not all crystal structures strictly obey the tecton-to-synthon-to-network self-assembly model: even closely related structures sometimes adopt different packing arrangements because of competition between electrostatic forces, hydrogen bonding, and van der Waals interactions.10 According to Desiraju, a proper understanding of molecule to crystal relationships is the challenge in crystal engineering.11

The design of new supramolecular architectures using molecular components of mixed (mismatched) symmetry is reported in the recent molecular tectonics literature. For example, Clearfield12 has designed robust 3D hexagonal frameworks from a self-complementary building block, nitrilotri(methylphosphonate) salts, in which tetrahedral functional groups are anchored on a trigonal molecule. Coppens13 cocrystallized [4]resorcinarene and tripyridyl triazine to assemble a trigonal prism molec-

NH4+, NH2NH3+, and OHNH3+ in Diamondoid Networks

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of anions. Notably, the trigonal H2CTA- anion functions as a four-connected node in four structures. Supramolecular build up of H2CTA- anion to the 6,4-adamantane network, 6,3-polyhexagon, or 4,4-square grid is shown to be related to the number of strong hydrogenbonding donor groups and the size of the ammonium cation. Results and Discussion The requisite ammonium salt was prepared by the treatment of H3CTA with an aqueous solution of RNH2 in alcohol to afford salts 1-5 after crystallization (see Experimental Section). Diffraction-quality single crystals were obtained in all cases except with MeNHNH2, which gave a powdery salt that is tentatively assigned the structure H2CTA-‚MeNH2+NH2. Attempted preparation of the complex with acetyl hydrazine gave the hydrazinium salt 4 through concomitant hydrolysis of the amide group during crystallization. NMR, IR, DSC, TGA, and X-ray diffraction confirmed the structures of new solids 1-5 and sodium salt 6, H2CTA-‚Na+. The crystal structure of 1 was solved and refined in the noncentrosymmetric space group Cc. Crystallographic details and structure refinement parameters are given in Table 1. Each molecule of H2CTA- is hydrogen bonded to four others in a tetrahedral array (Figure 2). Two neutral COOH donors are connected to different oxygen atoms of COO- via short and linear chargeassisted O-H‚‚‚O- hydrogen bonds (1.55 Å, 2.5366(16) Å, 177.8°; 1.57 Å, 2.5396(16) Å, 164.8°; neutron-normalized geometry is reported as d, D, θ in Table 2). The supramolecular tetrahedron of five H2CTA- anions is the building block for the diamond network (Figure 3) via O-H‚‚‚O- hydrogen bonds. The anionic framework is stabilized by negative charge-assisted short hydrogen bonds (energy 15-30 kcal/mol), which are an order of magnitude stronger than neutral hydrogen bonds (515 kcal/mol).15 The distance between the centers of

Figure 1. Crystal structure of H2CTA-‚(bipy-etebz2H+)0.5 to show the parquet grid layer with T-shaped H2CTA- anions at the nodes of the 6,3 network. Rectangular voids are filled by bipyridinium cations, which are not shown for clarity. Reproduced with permission from ref 7b. Copyright 2003 American Chemical Society.

ular polyhedron for guest inclusion, and MacGillivray14 reported that tetrapyridyl cyclobutane behaves as a three-connected node in its Cu complex. There are, however, no examples of the crystal engineering of diamondoid network structures based on ammonium carboxylates (Scheme 1c). X-ray crystal structures of H2CTA-‚NH4+ 1, H2CTA-‚MeNH3+ 2, H2CTA-‚EtNH3+ 3, H2CTA-‚NH2NH3+ 4, and H2CTA-‚OHNH3+ 5 are analyzed to understand how different ammonium counterions, RNH3+, influence the molecular conformation, hydrogen bonding, and topology of the anionic network in H2CTA- salts. Salts 1, 4, and 5 crystallize in the target 3D diamond network of H2CTA- anions, 2 forms a hexagonal layer, and 3 is organized in a square grid

Table 1. Crystal Data of Salts 1-6 in This Paper compound

1

2

3

4

5

6

formula Mr crystal system space group color crystal dimensions, mm a, Å b, Å c, Å R, ° β, ° γ, ° V, Å3 Z µ/mm-1 Fcalcd, g/cm3 2θmax, ° reflns collected independent reflns Rint R1 (I >2σ(I)) GOF max/min residual electron density, e/Å3 X-ray instrument T, K

C9H15NO6 233.22 monoclinic Cc colorless 0.5 × 0.35 × 0.24

C10H17NO6 247.25 monoclinic P21/c colorless 0.60 × 0.40 × 0.25

C11H19NO6 261.27 triclinic P1h colorless 0.43 × 0.24 × 0.18

C9H16N2O6 248.24 monoclinic Cc colorless 0.24 × 0.14 × 0.04

C9H15NO7 249.22 monoclinic Cc colorless 0.31 × 0.22 × 0.08

C9H11O6Na 238.17 monoclinic P21/n colorless 0.18 × 0.16 × 0.05

4.7608(11) 19.703(5) 11.502(3) 90 90.551(4) 90 1078.9(5) 4 0.121 1.436 56.58 4639 2330

5.8655(2) 17.805(12) 11.408(2) 90 93.70(3) 90 1189.0(4) 4 0.114 1.381 54.96 2979 2722

7.6682(9) 8.4743(10) 9.5164(12) 91.741(2) 94.436(2) 97.239(2) 611.13(13) 2 0.116 1.420 53.12 9073 2347

5.4329(14) 17.829(5) 11.820(3) 90 94.361(5) 90 1141.6(5) 4 0.122 1.444 56.00 3831 2245

5.0737(14) 18.203(5) 11.742(3) 90 93.275(4) 90 1082.7(5) 4 0.133 1.529 55.82 3604 1969

9.2006(14) 4.9116(8) 21.385(3) 90 96.835(5) 90 959.5(3) 4 0.176 1.649 56.62 7977 2371

0.0209 0.030 1.030 0.35/-0.19

0.0360 0.062 1.009 0.22/-0.24

0.0241 0.040 1.095 0.29/-0.22

0.0385 0.041 1.003 0.21/-0.21

0.0220 0.031 1.058 0.20/-0.16

0.0779 0.042 0.936 0.281/-0.314

Bruker-CCD Smart 1000 93

Enraf-Nonius MACH-3 293





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Figure 2. Tetrahedral assembly of five H2CTA- molecules connected via O-H‚‚‚O- hydrogen bonds in 1, shown as a stereoview. The trigonal molecule at the center of the tetrahedron behaves like a tetrahedral node through two COOH donors and a COOgroup as a double acceptor. W A 3D rotatable image in PDB format is available.

cyclohexane rings at the nodes of the diamond network (7.32, 9.57 Å) is comparable to the internode distance in methanetetraacetic acid (8.76 Å).6a The tetrahedral angles in 1 (91.2-129.6°) deviate from the ideal value of 109.5°, but they are within the accepted range for diamond-like nets6,8,16 (e.g., methanetetraacetic acid 79.8, 126.1°). The super-adamantane framework has spherical cavities of 10-11 Å diameter, which are filled by two identical networks interweaving through the voids.17 NH4+ counterions occupy channels left over in the triply interpenetrated network and are strongly bonded to the anions (Figure 4): N+-H‚‚‚O- 1.90 Å, 2.8710(18) Å, 158.6°; 1.91 Å, 2.9025(17) Å, 165.2°; N+H‚‚‚O 1.92 Å, 2.8284(18) Å, 147.7°; 1.97 Å, 2.8880(19) Å, 149.6°. The packing of 3-fold interpenetrated diamond net in 1 is akin to the intertwining of three 4/1 helices of H2CTA-, which form anionic walls around the NH4+ ion channel along [100].6b,18 The diamondoid network structure of 1 is unique among the 150 or so ammonium carboxylate salts published in the Cambridge Structural Database (CSD).19 NH4+ donors in 1 hydrogen bond to acceptor oxygen atoms of four different molecules, in contrast to bifurcated N+-H‚‚‚O hydrogen bonds in several structures. Some common packing arrangements in the CSD are (1) square motif I (Scheme 2) of N+-H‚‚‚O hydrogen bonds from alternating ammonium and COOH/COO- groups; (2) even in cases in which NH4+ approaches four different O atoms, the structure does not adopt the adamantane network because the carboxylate molecule is not a tetraheral node; (3) dimer-type motifs between COOH groups (e.g., Figure 1 and salt 2 is discussed next) reduce node connectivity at the carboxylate molecule to three. A manual inspection of the published structures showed that the crystal structure of ammonium hydrogen bis(trichloroacetate), Cl3CCOOH‚Cl3CCOO-‚NH4+ (CSD refcode AMHTCA),20a adopts the diamond network in I-42d space group (No. 122). However, the anions do not form an infinite network, as in 1, but instead form dimers of O-H‚‚‚O- hydrogen bonds and these dimers are bonded to NH4+ cations at the nodes. Methylammonium complex 2 crystallizes in the centrosymmetric space group P21/c. Charge-assisted OH‚‚‚O- hydrogen bonds between H2CTA- molecules make a polycyclohexane grid when the centers of the

cyclohexane rings are treated as three-connected nodes (Figure 5a). These 6,3 networks stack along the a-axis to form channels, which are filled by MeNH3+ cations. Strong hydrogen bonds N+-H‚‚‚O- (2.807(4), 2.862(4) Å), N+-H‚‚‚O (2.961(4) Å) and weak C-H‚‚‚O interactions (C‚‚‚O: 3.2-3.6 Å) stabilize the cation-anion assembly (Figure 5b). The polycyclohexane framework in 2 resembles a black phosphorus 2D network,21 which may be carved from the diamondoid net of 1. There are two notable features in 2. (1) The neutral COOH groups of H2CTA- are present in syn and anti conformations (Scheme 2).22 The anti COOH engages in dimer O-H‚‚‚O- H bonds via motif II, whereas the syn COOH makes a single O-H‚‚‚O- hydrogen bond (2.546(4), 2.568(3) Å). (2) Hydrogen bonding in heterosynthon III does not follow the strongest-donor to strongest-acceptor hierarchy23 because the stronger NH+ donor bonds to the weaker OH acceptor and the weaker CH donor interacts with the stronger CdO acceptor. Two recent examples of nonhierarchic hydrogen bonding24 have been explained as follows: (1) in dicarboxylic acidisonicotinamide complexes,24a the acceptor strengths of electronegative groups competing for the same donor hydrogen are comparable, and the resulting hydrogenbond synthons have similar energies; (2) the importance of geometric fit over pKa differences between donor and acceptor groups in the cocrystallization of diacids with a triazole drug molecule.24b We propose that the strong O-H‚‚‚O- hydrogen bond of motif II sufficiently activates the anti OH group so that it, in effect, becomes a stronger acceptor than CdO, which is traditionally believed to be the better acceptor group of COOH. The situation here is analogous to the water acceptor in pyrazine tetracarboxylic acid,25 where we noted that the calculated electrostatic surface potential of the O atom in hydrogen-bonded water is significantly greater than free water (free water -46.2 kcal/mol, hydrogen-bonded water -64.4 to -65.2 kcal/mol). This means that acceptor strengths in networks of hydrogen bonds can be quite different from the values of isolated groups, and this fact should be borne in mind when several donors and acceptors are present in the same system. The extended network of hydrogen bonds in motifs II and III perhaps stabilizes the rare anti conformation of the COOH group.



Table 2. Hydrogen-Bond Parameters and Network Dimensions in Crystal Structures 1-6

a

Acceptor is the OH group of COOH. b Donor OH is from NH3+OH.

The crystal structure of EtNH3+ salt 3 is quite different from 2. Here, each H2CTA- is bonded to four different molecules via O-H‚‚‚O- hydrogen bonds in a square network20b (2.5449(15), 2.5861(17) Å). EtNH3+ cations fill the square voids and also connect neighboring layers via ionic N+-H‚‚‚O- hydrogen bonds (2.7263(17), 2.8999(17), 2.8986(17) Å) and weak C-H‚‚‚O interactions (3.4-3.6 Å) (Figure 6). The 2D square network in Figure 6a has a polar arrangement, in that COOH and COO- groups within a layer are aligned in the same direction. However, adjacent layers are inversion-related in the centrosymmetric crystal structure

(P1 h ). Comparison of structures 1 and 3 shows that the anionic network is derived from a four-connected node in both structures, but the latter structure is layered because the fourth strong hydrogen-bonding group is absent in the counterion. The O-H‚‚‚O- motif surrounding the ammonium cation is helical in 1, whereas it is cyclic in 3, cf. Figures 4a and 6b. This suggested that the fourth hydrogen-bonding group in the ammonium cation must also be strong to extend the layer structure to the third dimension. We therefore replaced the ethyl group by strong hydrogen-bonding NH2 and OH groups in RNH3+ to construct the diamond network.

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Figure 3. Stereoview of the adamantane network (solid lines) of O-H‚‚‚O- hydrogen bonds in 1 to show H2CTA- molecules at the tetrahedral nodes. NH4+ ions are not shown for clarity. W A 3D rotatable image in PDB format is available.

Crystal engineering of the diamond network of H2CTAin NH2NH3+ and OHNH3+ salts 4 and 5 is now discussed. The crystal structure of salt 4 was solved and refined in the noncentrosymmetric space group Cc. It is nearly identical to 1 in all respects: tetrahedral organization of the anions, arrangement of the cations in the channels, network dimensions, and the interpenetration mode. Thus, the symmetric NH4+ counterion is isostructurally replaced by NH2NH3+ in the triply interpenetrated diamond network of 4. The three NH+ donors of hydrazinium cation exactly replace the ammonium cation and the neutral NH approximately occupies the fourth coordination region with N‚‚‚O distances of 2.779(3), 2.866(3), 2.771(3), and 3.201(4) Å (Table 2). Examination of the interior of the structure, however, shows that the fifth NH is somewhat weakly hydrogen-bonded to the CdO acceptor (N‚‚‚O 3.211(4) Å). This led us to employ OHNH3+ as another surrogate for the tetrahedral cation. Once again, the crystal structure of salt 5 is isostructural (Figure 7). The only difference between these noncentrosymmetric diamond network structures is a small variation in cell parameters (Table 1) to accommodate counterions of varying size (NH4+, NH2NH3+, OHNH3+ ) 21.2, 33.7, 31.1 Å3). The unit cell similarity index, Π,26 of 4 and 5 compared to 1 is 0.025 and 0.027, implying near identity between these crystal structures. Noncentrosymmetric diamond nets based on the NH4+ cation and linear bipyridine N-oxide connectors were reported recently.27 The present structures are different in that the diamond network is purely anionic, and the role of the ammonium cation is to orient the acidic groups of the trigonal H2CTA- anion in the shape of a tetrahedral tecton. Furthermore, this is the first observation on the equivalence of NH4+, NH2NH3+, and OHNH3+ in templating isostructural diamond networks.28 The fact that diamond nets are obtained with these counterions whereas the structures are different for the two alkylammonium cations studied means that tetrahedral cations with four strong hydrogen-bonding

groups serve as a template in guiding the orientation of the COOH and COO- residues in a tetrahedral arrangement. The combination of asymmetrical tetrahedral node, unsymmetrical O-H‚‚‚O- node connector, and odd-fold interpenetration generally favor crystallization in noncentrosymmetric space groups.29 However, when the node connector is symmetric (e.g., methanetetraacetic acid),6a or the degree of interpenetration is even-fold (e.g., as in some metal-organic diamond nets),8d the structures are usually centrosymmetric. The polar diamond network in 1, 4, and 5 is similar to the anionic network in the NLO material potassium dihydrogen phosphate (KDP)30 and also to the disodium and dipotassium salts of 1,3,5,7-adamantanetetracarboxylic acid.6b SHG activity of salts 1, 4, and 5 was measured by the powder test at 1.06 µm (Nd3+YAG laser). The intensity of green signal at 530 nm is qualitatively comparable to that of KDP (0.3 × urea) suggesting practical development of these stable materials in electrooptics. The sinusoidal chain of cations and anions (motif IV, Scheme 2) along the c-glide in these noncentrosymmetric structures could be responsible for their NLO behavior. Salts 1, 4, and 5 do not show any decomposition up to their melting point in thermal gravimetric analysis (TGA). They are also transparent in the UV-vis region above 250 nm. The construction of the diamondoid network in 1 and its related salts is conceptually different from the known examples of diamond nets because the builder molecule is a trigonal tricarboxylic acid compared to tetrahedral tetracarboxylic acids used earlier. Whereas the two COO- groups act as single hydrogen-bond acceptors in adamantane tetracarboxylates,6b the single COO- in trigonal anion 1 functions as a double hydrogen-bond acceptor. We analyze two factors that promote the new supramolecular transformation from trigonal molecule to tetrahedral tecton to diamondoid network in H2CTAsalts: (1) conformational flexibility of the carboxylic acid groups, and (2) tetrahedral orientation of four strong hydrogen-bond donors in the ammonium counterion.


Crystal Growth & Design, Vol. 5, No. 3, 2005 1277 Scheme 2. Some Common Hydrogen-Bond Synthons in Ammonium Carboxylate Salts Discussed in This Paper

Figure 4. (a) NH4+‚‚‚H2CTA- hydrogen bonding in 1 viewed down the a-axis. Note that each NH4+ ion is hydrogen bonded to four different H2CTA- anions, two molecules belonging to the blue network and one molecule each of the red and green networks. (b) The triply interpenetrated diamondoid networks are separated by 4.76 Å () a-axis) and NH4+ ions occupy the channels left over after catenation. W A 3D rotatable image of panel a in PDB format is available.

Superposition of H2CTA- anions (Figure 8) shows that the chair cyclohexane rings overlay nicely but the carboxylic acid groups adopt different orientations and conformations depending on electrostatic interactions, hydrogen bonds with counterion, and crystal packing forces. The ammonium cations in salts 1, 4, and 5 are able to template the tetrahedral organization of acidic O-atoms due to the conformational flexibility of COOH/ COO- groups in H2CTA-. In contrast, acidic residues of trimesate anion (H2TMA-) are clustered in the plane of the benzene ring (see Supporting Information for the overlay diagram). The function of H2CTA- as a fourconnected tetrahedral node in diamond nets is in contrast to the usual role of triacid anions (e.g.,

trimesate5b,d and H2CTA salts7b-d) as three-connected nodes in honeycomb networks. The cyclohexane ring surely plays a role because the complex (NH4+)1.5‚[1,3,5C6H3(CH2COOH)1.5 (CH2COO-)1.5],31 in which conformationally flexible carboxylic acid groups are anchored on an aromatic core, does not exhibit diamond network but instead has a doubly interpenetrated 1D ladder network. Ladder networks have been identified in several dialkylammonium salts in a recent database analysis of crystal structures.32 The normal behavior of C3 tricarboxylic acids, as building blocks for 2D honeycomb layer structures, is changed by the ammonium counterion template to give diamond architectures in H2CTA-. It has been shown that trigonal ligands (e.g., cyclotriveratrylene) self-assemble to tetrahedral (CTV)4 clusters in the presence of ditopic metal atoms.33 The significance of four strong hydrogen-bonding groups on the ammonium cation for generating diamond nets (point (2) above) is manifested in the supramolecular build up of these network structures. The three NH+ donors of NH4+, NH2NH3+, OHNH3+, and MeNH3+ orient toward acceptor oxygen atoms in a near identical arrangement. When the fourth hydrogen-bond donor is strong, NH or OH, crystal growth progresses to the (6,4) adamantane network (e.g., 1, 4, 5), whereas the structure is truncated to (6,3) cyclohexane network when the donor is weak (e.g., CH3 group in 2; Figure 9). Moreover, space groups of these crystal structures are also related: Cc and P21/c are remote subgroups of the cubic diamond lattice (Fd3 h m). The geometry of the fourconnected H2CTA- node is square in 3 and tetrahedral in 1 because EtNH3+ counterion has only three strong hydrogen-bonding groups instead of four in NH4+. Both square and adamantane networks have been observed in the crystal structures of a tetrahedral tecton.34 The question as to whether the syn and anti conformations of the COOH group in 2 or the syn COOH groups of 3 (orange and yellow colored H2CTA- anions in Figure 8) represent the “normal” structure in the 2D layered salts is difficult to predict with the limited structural data.

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Figure 5. (a) O-H‚‚‚O- hydrogen bonds and motif II connect H2CTA- anions in the polycyclohexane network of salt 2. The anti-COOHs form the dimer motif II. (b) CH3NH3+ cations are hydrogen bonded to the walls of the anionic channels via N+H‚‚‚O- hydrogen bonds and heterosynthon III.

Figure 6. (a) Square networks of O-H‚‚‚O- hydrogen bonds extend to form 2D polar sheets of H2CTA- molecules in 3. (b) CH3CH2NH3+ cations fill the square voids and also connect adjacent inversion-related layers.

Crystallographic analysis of H2CTA-‚RNH3+ salts with different R groups will show the trend in this family.

not only on the difference electron density maps but also on C-O distances and reasonable hydrogen-bond geometries.

As a further test for the importance of a tetrahedral ammonium cation in these salts, NH4+ was replaced by an isotropic counterion in H2CTA-‚Na+ 6 (space group P21/n). This structure has β-arsenic sheets of carboxylate molecules intercalated by Na+ cations (Figure 10). The β-arsenic topology of 6 may be compared with the black phosphorus network in 2 (Figure 9b), emphasizing the importance of counterion in directing the anionic framework. The corresponding potassium salt, H2CTA-‚K+, has so far not afforded single crystals suitable for X-ray diffraction. There is a confluence of chemical reactivity and directional hydrogen bonding in H2CTA-‚RNH3+ salts 1, 4, and 5 to generate the diamond network: deprotonation results in the ammonium cation, which, in turn, reveals the latent fourconnected tetrahedral node in the trigonal carboxylate. Since the hydrogen atoms positions are determined by X-ray diffraction only with a limited accuracy, the placement of hydrogen atoms in salts 1-6 and the assignment of neutral or ionic carboxyl group are based

Conclusions Trigonal and tetrahedral tectons have been employed to build hexagonal and diamond network structures, respectively. There is now increasing interest in developing novel supramolecular transformations using molecular components of different symmetry to access solids with new and diverse architectures.12-14 We have shown in this paper that a conformationally flexible trigonal tricarboxylic acid functions as a tetrahedral tecton in the presence of suitable ammonium cation templates. This novel supramolecular transformation in H2CTA-‚RNH3+ crystals offers a rapid cocrystallization route to stable interpenetrated diamond networks compared to tetrahedral tectons and linear spacers as the building blocks. The equivalence of NH4+, NH2NH3+, and OHNH3+ in noncentrosymmetric diamond networks of H2CTA- and their good SHG activity demonstrate crystal engineering of solids with desired structure as well as useful function. Our results show that conformationally flexible tectons, hitherto less frequently



Figure 9. Similar arrangement of H2CTA- anions and RNH3+ cations in the 3D diamond network of 1 (a) and the super black phosphorus 2D layer of 2 (b). Hydrogen bonds connecting the super black P sheets to the third dimension (e.g., green networks in 1) are absent in 2 showing that four strong hydrogen-bond donors are required on the ammonium ion template to direct the diamond network of H2CTA- anions.

Figure 7. Triply interpenetrated diamond network in the crystal structure of H2CTA-‚NH2NH3+ 4 (a) and H2CTA-‚ OHNH3+ 5 (b). Translation-related nets are separated by 5.43 and 5.07 Å () a-axis). Note the isostructurality with Figure 4b.

Figure 10. β-Arsenic sheet of H2CTA- anions in 6. Sodium ions are intercalated between these sheets (not shown).

Figure 8. Overlay of H2CTA- molecules in 1-6. COOH/COOgroups adopt different conformations depending on the cation structure (dark blue ) 1, orange ) 2, yellow ) 3, pink ) 4, light green ) 5, light blue ) 6). Note the tight overlay of COOH and COO- groups in adamantane structures 1, 4, and 5. COOgroup is in the center and COOH groups are on the sides. See Supporting Information for the overlay diagram that includes H2CTA- structures from the CSD.

used in crystal engineering, have considerable potential in generating supramolecular diversity through novel recognition modes. Modular build up from the 2D hexagonal layer to the 3D diamond network suggests that the present transformation should be amenable to

crystal design starting from other trigonal molecules and tetrahedral functional groups. To summarize, our results show (1) cyclohexane tricarboxylate is a new four-connected building block; (2) the equivalence of NH4+, NH2NH3+, and OHNH3+ as a tetrahedral template; and (3) crystal engineering of noncentrosymmetric diamond network structures for potential NLO and ferroelectric materials. Experimental Section Synthesis. Salts 1-6 were prepared by the deprotonation of H3CTA with a stoichiometric equivalent of the appropriate base (NH3, MeNH2, EtNH2, NH2NH2, OHNH2, and NaOH) in aq. MeOH/EtOH. The product was allowed to crystallize over a few days. These compounds exhibit a sharp melting endotherm (DSC) and are stable up to their melting point (TGA). H2CTA-‚NH4+ 1. 1,3-cis,5-cis-Cyclohexanetricarboxylic acid (108 mg, 0.5 mmol) was dissolved in 1 mL of MeOH and 30% aqueous NH3 (32 µL, 0.5 mmol) was added. The vial was closed

1280


and shaken for a minute. After complete precipitation of salt 1 (ca. 1 h), MeOH was decanted, and the precipitate was washed with 1 mL of MeOH. Crystallization from hot MeOH gave single crystals suitable for X-ray diffraction after 2 days. mp 231 °C (Tonset, DSC). H2CTA-‚MeNH3+ 2. Prepared by the same procedure as 1. Crystallization from hot EtOH gave single crystals in 3-4 days. mp 221 °C (Tonset, DSC). H2CTA-‚EtNH3+ 3. H3CTA (65 mg, 0.3 mmol) was dissolved in about 1 mL of EtOH, and 70% aqueous EtNH2 (29 µL, 0.4 mmol) was added. To this solution, CHCl3 was added until the turbidity appeared, and the mixture was then heated to get a clear solution. Crystals of 3 appeared after a day (mp 155160 °C). H2CTA-‚NH2NH3+ 4. H3CTA (65 mg, 0.3 mmol) was dissolved in 1 mL of MeOH, and 80% aq. NH2NH2 (20 µL, 0.3 mmol) was added. The vial was closed and shaken for a minute. After complete precipitation of H2CTA-‚N2H5+ salt (ca. 1 h), MeOH was decanted and the precipitate was washed with l mL of MeOH. Crystallization from hot MeOH yielded crystals in 2 days. mp 195 °C (Tonset, DSC). H2CTA-‚OHNH3+ 5. H3CTA (43 mg, 0.2 mmol) was dissolved in 1 mL of MeOH, and 50% aq. OHNH2 (20 µL, 0.3 mmol) was added. The vial was closed and shaken for a minute, and the mixture was kept in the refrigerator for crystallization. Crystals of H2CTA-‚OHNH3+ were obtained after 2 days. mp 180 °C (Tonset, DSC). There was decomposition of hydroxylamine when crystallization was carried out at ambient temperature. H2CTA-‚Na+ 6. NaOH (12 mg, 0.3 mmol) in 2 mL of aq. MeOH was added to 1 mL of methanolic H3CTA (65 mg, 0.3 mmol), the sample was heated on a water bath, and the solvent was evaporated under vacuum. The solid was washed with MeOH and crystallized in hot aq. MeOH. Crystals were obtained after one week. mp 322 °C (Tonset, DSC). All salts are stable and do not show any decomposition up to their melting point (TGA). TGA and DSC. Differential scanning calorimetry (DSC) was performed on a Mettler Toledo DSC 822e module, and thermal gravimetry (TG) was performed on a Mettler Toledo TGA/SDTA 851e module. Crystals taken from the mother liquor were blotted dry on filter paper and placed in open alumina pans for TG experiments and in crimped but vented aluminum sample pans for DSC experiments. Sample size in each case was 5-7 mg. The sample was heated from 30 to 300 °C at a rate of 10 °C/min. The samples were purged with a flow of dry nitrogen at 150 mL/min for DSC and 50 mL/min for TG runs. UV-Vis Spectra. UV-Vis spectra of 1, 4, and 5 were recorded on Shimadzu 3101-PC UV/Vis/NIR spectrophotometer in MeOH solution. λmax ∼ 220-225 nm ( ∼ 200-300). These salts are transparent beyond 250 nm. X-ray Crystallography. Details of X-ray data for salts 1-6 are given in Table 1 (Mo-KR radiation, λ ) 0.71073 Å). Structures were solved by the direct methods and refined on F2 with SHELX-9735 and SHELXTL.36 Non-hydrogen atoms were refined anisotropically in all structures. All hydrogen atoms in 1, 2 and only acidic hydrogen atoms (OH/NH) in 3-6 were located from difference Fourier maps. Hydrogen atoms bonded to carbon in 3-6 were fixed in calculated positions. NLO Activity. SHG measurements on microcrystalline samples of 1, 4, and 5 were carried out using a Nd3+-YAG laser at 1064 nm. These samples showed a green signal at 532 nm with quadratic nonlinear efficiency approximately 0.3 times that of urea (0.3 × U ) KDP). Powder X-ray Diffraction. PXRD of salts 1, 4, and 5 were recorded on a Philips powder diffractometer (Cu KR1 radiation, λ ) 1.54056 Å). The bulk material is identical to the crystalline salt.

Acknowledgment. A.N. acknowledges research funding from CSIR (01/1738/02/EMR-II) and DST (SR/S5/ OC-02/2002). B.R.B. and P.V. are research fellows of UGC and CSIR. We thank DST (IRPHA) for the X-ray

Bhogala et al.

diffractometer facility and the UPE program of UGC for support to UoH. We thank Dr. J. L. Flippen-Anderson and Dr. J. R. Deschamps of Naval Research Laboratory, Washington DC, U.S.A., and Mr. A. Lemmerer, Prof. D. G. Billing of University of Witwatersrand, Wits, South Africa, for assistance with X-ray data. Prof. J. -F. Nicoud, Universite´ Louis Pasteur, Strasbourg, France, carried out the SHG measurements. Supporting Information Available: Crystallographic data (.cif) of the salts listed in Table 1 and overlay diagrams are available via the Internet at http://pubs.acs.org.

References (1) (a) Desiraju, G. R. Angew. Chem., Int. Ed. Engl. 1995, 34, 2311. (b) MacNicol, D. D., Toda, F., Bishop, R., Eds.; Comprehensive Supramolecular Chemistry, Volume 6, SolidState Supramolecular Chemistry: Crystal Engineering; Pergamon: Oxford, 1996. (c) Ermer, O. J. Am. Chem. Soc. 1988, 110, 3747. (2) (a) Wuest, J. D. in Mesomolecules: From Molecules to Materials; Mendenhall, G. D., Greenberg, A., Liebman, J. F., Eds.; Chapman & Hall: New York, 1995; Volume 1, pp 107-131. (b) Mann, S. Nature 1993, 365, 499. (3) (a) Martz, J.; Graf, E.; Cian, A. D.; Hosseini, M. W. in Crystal Design and Function, Perspectives in Supramolecular Chemistry; Desiraju, G. R., Ed.; Wiley: Chichester, 2003; Volume 7, pp 177-209. (b) Hosseini, M. W. CrystEngComm 2004, 6, 318. (4) (a) Saladino, R.; Hanessian, S. in Crystal Design and Function, Perspectives in Supramolecular Chemistry; Desiraju; G. R., Ed.; Wiley: Chichester, 2003; , Volume 7, pp 77-151. (b) Grosshans, P.; Jouaiti, A.; Bulach, V.; Planeix, J.-M.; Hosseini, M. W.; Nicoud, J.-F. Chem. Commun. 2003, 1336. (c) Wu, C.-D.; Lu, C.-Z.; Lin, X.; Wu, D.-M.; Lu, S.-F.; Zhuang, H.-H.; Huang, J.-S. Chem. Commun. 2003, 1284. (d) Yue, W.; Bishop, R.; Craig, D. C.; Scudder, M. L. Tetrahedron 2000, 56, 6667. (5) (a) Kolotuchin, S. V.; Fenlon, E. E.; Wilson, S. R.; Loweth, C. J.; Zimmerman, S. C. Angew. Chem., Int. Ed. Engl. 1995, 34, 2654. (b) Melendez, R. E.; Sharma, C. V. K.; Zaworotko, M. J.; Bauer, C.; Rogers, R. D. Angew. Chem., Int. Ed. Engl. 1996, 35, 2213. (c) Ranganathan, A.; Pedireddi, V. R.; Rao, C. N. R. J. Am. Chem. Soc. 1999, 121, 1752. (d) Plaut, D. J.; Lund, K. M.; Ward, M. D. Chem. Commun. 2000, 769. (e) Jetti, R. K. R.; Thallapally, P. K.; Xue, F.; Mak, T. C. W.; Nangia, A. Tetrahedron 2000, 56, 6707. (f) Mak, T. C. W.; Xue, F. J. Am. Chem. Soc. 2000, 122, 9860. (g) Zaworotko, M. J. Chem. Commun. 2001, 1. (h) Holman, K. T.; Pivovar, A. M.; Swift, J. A.; Ward, M. D. Acc. Chem. Res. 2001, 34, 107. (i) Jetti, R. K. R.; Thallapally, P. K.; Nangia, A.; Lam, C.-K.; Mak, T. C. W. Chem. Commun. 2002, 952. (j) Ma, B.-Q.; Coppens, P. Chem. Commun. 2003, 2290. (6) (a) Ermer, O.; Eling, A. Angew. Chem., Int. Ed. Engl. 1988, 27, 829. (b) Ermer, O.; Lindenberg, L. Chem. Ber. 1990, 123, 1111. (c) Reddy, D. S.; Craig, D. C.; Desiraju, G. R. J. Am. Chem. Soc. 1996, 118, 4090. (d) Galoppini, E.; Gilardi, R. Chem. Commun. 1999, 173. (e) Reddy, D. S.; Dewa, T.; Endo, K.; Aoyama, Y. Angew. Chem., Int. Ed. 2000, 39, 4266. (f) Thaimattam, R.; Sharma, C. V. K.; Clearfield, A.; Desiraju, G. R. Cryst. Growth Des. 2001, 1, 103. (g) Guo, W.; Galoppini, E.; Gilardi, R.; Rydja, G. I.; Chen, Y.-H. Cryst. Growth Des. 2001, 1, 231. (h) Ermer, O.; Kusch, A.; Ro¨bke, C. Helv. Chim. Acta 2003, 86, 922. (i) Fournier, J.-H.; Maris, T.; Wuest, J. D.; Guo, W.; Galoppini, E. J. Am. Chem. Soc. 2003, 125, 1002. (j) Fournier, J.-H.; Maris, T.; Simard, M.; Wuest, J. D. Cryst. Growth Des. 2003, 3, 535. (k) Lindemann, S. V.; Hecht, J.; Kochi, J. K. J. Am. Chem. Soc. 2003, 125, 11597. (l) Brunet, P.; Demers, E.; Maris, T.; Enright, G. D.; Wuest, J. D. Angew Chem. Int. Ed. 2003, 42, 5303. (7) (a) Bhogala, B. R.; Vishweshwar, P.; Nangia, A. Cryst. Growth Des. 2002, 2, 325. (b) Bhogala, B. R.; Nangia, A. Cryst. Growth Des. 2003, 3, 547. (c) Molecular salts of H3-



CTA with 1,3-bis(4-pyridyl)propane and 1,4-bis(4-pyridyl)butane have β-As sheet 6,3-network, unpublished results. (d) Shan, N.; Bond, A. D.; Jones, W. New J. Chem. 2003, 27, 365. (e) Ermer, O.; Neudo¨rfl, J. Chem. Eur. J. 2001, 7, 4961. Metal-organic or hybrid structures are discussed in excellent reviews (a-e) and new examples continue to be reported (f-i). (a) Zaworotko, M. J. Chem. Soc. Rev. 1994, 283. (b) Moulton, B.; Zaworotko, M. J. Chem. Rev. 2001, 101, 1629. (c) Eddaoudi, M.; Moler, B. B.; Li, H.; Chen, B.; Reineke, T. M.; O’Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2001, 34, 319. (d) Evans, O. R.; Lin, W. Acc. Chem. Res. 2002, 35, 511. (e) James, S. L. Chem. Soc. Rev. 2003, 32, 276. (f) Li, X.; Cao, R.; Sun, D.; Bi, W.; Wang, Y.; Li, X.; Hong, M. Cryst. Growth Des. 2004, 4, 775. (g) Du, M.; Guo, Y.-M.; Chen, S.T.; Bu, X.-H.; Batten, S. R.; Ribas, J.; Kitagawa, S. Inorg. Chem. 2004, 43, 1287. (h) Fuma, Y.; Ebihara, M.; Kutsumizu, S.; Kawamura, T. J. Am. Chem. Soc. 2004, 126, 12238. (i) Li, X.; Cao, R.; Sun, D.; Bi, W.; Wang, Y.; Li, X.; Hong, M. Cryst. Growth Des. 2004, 4, 775. Biradha, K.; Dennis, D.; MacKinnon, V. A.; Sharma, C. V. K.; Zaworotko, M. J. J. Am. Chem. Soc. 1998, 120, 11894. Angeloni, A.; Crawford, P. C.; Orpen, A. G.; Podesta, T. J.; Shore, B. J. Chem. Eur. J. 2004, 10, 3783. Vangala, V. R.; Bhogala, B. R.; Dey, A.; Desiraju, G. R.; Broder, C. K.; Smith, P. S.; Mondal, R.; Howard, J. A. K.; Wilson, C. C. J. Am. Chem. Soc. 2003, 125, 14495. Sharma, C. V. K.; Clearfield, A. J. Am. Chem. Soc. 2000, 122, 4394. (a) Ma, B.-Q.; Coppens, P. Chem. Commun. 2004, 932. (b) Ma, B.-Q.; Coppens, P. Cryst. Growth Des. 2004, 4, 211. Hamilton, T. D.; Papaefstathiou, G. S.; MacGillivray, L. R. J. Am. Chem. Soc. 2002, 124, 11606. (a) Jeffrey, G. A. An Introduction to Hydrogen Bonding; Oxford University Press: Oxford, 1997. (b) Steiner, T. Angew. Chem., Int. Ed. 2002, 41, 48. (a) Evans, O. R.; Lin, W. Chem. Mater. 2001, 13, 2705. (b) Carlucci, L.; Ciani, G.; Proserpio, D. M.; Rizzato, S. Chem. Eur. J. 2002, 8, 1520. (c) Xiong, R.-G.; J.-L.; Zuo, You, X.Z.; Abrahams, B. F.; Bai, Z.-P.; Che, C.-M.; Fun, H.-K. Chem. Commun. 2000, 2061. (a) Batten, S. R.; Robson, R. Angew. Chem., Int. Ed. 1998, 37, 1460. (b) Batten, S. R. CrystEngComm 2001, 3, 67. Hirsh, K. A.; Wilson, S. R.; Moore, J. S. Chem. Eur. J. 1997, 3, 765. ConQuest, July 2004 update of the CSD (www. ccdc.cam.ac.uk) contains 148 organic crystal structures with NH4+ and COO- fragments. There is one example each of diamond (AMHTCA)20a and square (diammonium dihydrogen pyromellitate, PAHXOL)20b networks among the CSD hits.19 (a) Golic, L.; Lazarini, F. Cryst. Struct. Commun. 1975, 4, 487. (b) Jessen, S. M.; Kuppers, H.; Luehrs, D. C. Z. Naturforsch, Teil. B, Chem. Sci. 1992, 47, 1141.

(21) Ermer, O.; Eling, A. J. Chem. Soc., Perkin Trans. 2 1994, 925. (22) The frequency of syn and anti COOH conformers was analyzed recently. Kuduva, S. S.; Craig, D. C.; Nangia, A.; Desiraju, G. R. J. Am. Chem. Soc. 1999, 121, 1936. (23) Etter, M. C. J. Phys. Chem. 1991, 95, 4601. (24) (a) Vishweshwar, P.; Nangia, A.; Lynch, V. M. Cryst. Growth. Des. 2003, 3, 783. (b) Remenar, J. F.; Morissette, S. L.; Peterson, M. L.; Moulton, B.; MacPhee, J. M.; Guzman, H. R.; Almarsson, O ¨ . J. Am. Chem. Soc. 2003, 125, 8456. (25) Vishweshwar, P.; Babu, N. J.; Nangia, A.; Mason, S. A.; Puschmann, H.; Mondal, R.; Howard, J. A. K. J. Phys. Chem. A 2004, 108, 9406. (26) (a) Fa´bia´n, L.; Ka´lma´n, A. Acta Crystallogr., Sect. B 1999, 55, 1099. (b) Π ) (a + b + c ÷ a′ + b′ + c′) - 1 using orthogonalized lattice parameters of the two unit cells being compared. (27) Ma, B.-Q.; Sun, H.-L.; Gao, S. Chem. Commun. 2003, 2164. (28) Some examples of crystal structures based on ammonium ions. (a) Akutagawa, T.; Hasegawa, T.; Nakamura, T.; Inabe, T. J. Am. Chem. Soc. 2002, 124, 8903. (b) Du, B.; Meyers, E. A.; Shore, S. G. Inorg. Chem. 2001, 40, 4353. (c) Do, J.; Bontchev, R. P.; Jacobson, A. J. Inorg. Chem. 2000, 39, 4305. (d) Trueblood, K. N.; Knobler, C. B.; Lawrence, D. S.; Stevens, R. V. J. Am. Chem. Soc. 1982, 104, 1355. (29) While both salt 1 and methanetetraacetic acid have tetrahedral nodes and 3-fold interpenetration, the former structure is noncentrosymmetric because the O-H‚‚‚O- hydrogen bond is an unsymmetrical connector whereas the latter structure is centrosymmetric because the carboxylic acid O-H‚‚‚O dimer is a symmetric interaction. (30) Nicoud, J.-F.; Twieg R. J. in Nonlinear Optical Properties of Organic Molecules and Crystals; Chemla, D. S., Zyss J., Eds.; Academic Press: Orlando, 1987; pp 221-254. (31) Zhu, H.-F.; Fan, J.; Okamura, T.; Sun, W.-Y.; Ueyama, N. Chem. Lett. 2002, 898. (32) Bond, A. D. Chem. Eur. J. 2004, 10, 1885. (33) (a) Hardie, M. J.; Raston, C. L.; Salinas, A. Chem. Commun. 2001, 1850. (b) Schweiger, M.; Seidel, S. R.; Schmitz, M.; Stang, P. J. Org. Lett. 2000, 2, 1255. (c) Hamilton, T. D.; MacGillivray, L. R. Cryst. Growth. Des. 2004, 4, 419. (34) Wang, X.; Simard, M.; Wuest, J. D. J. Am. Chem. Soc. 1994, 116, 12119. (35) (a) Sheldrick, G. M. SHELXS-97: Program for the Solution of Crystal Structures; University of Go¨ttingen, Germany, 1997. (b) Sheldrick, G. M. SHELXL-97: Program for Crystal Structure Refinement; University of Go¨ttingen, Germany, 1997. (36) SHELXTL: Program for the Solution and Refinement of Crystal Structures, version 6.14; Bruker AXS: Wisconsin, 2000.

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CG0500270

Equivalence of NH - American Chemical Society

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