Extending Primary Ammonium Dicarboxylate (PAD) to Diprimary

Article pubs.acs.org/crystal

Extending Primary Ammonium Dicarboxylate (PAD) to Diprimary Ammonium Dicarboxylate (DPAD) Synthon and Its Implication in Supramolecular Gelation Uttam Kumar Das and Parthasarathi Dastidar* Department of Organic Chemistry, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata − 700032, West Bengal, India S Supporting Information *

ABSTRACT: A series of organic salts derived from various dicarboxylic acids and two α,ω-diamines, namely, 1,3-diaminopropane and 1,4-diaminobutane, were prepared and characterized by various physicochemical techniques, including single-crystal X-ray diffraction, with the aim of extending the well-studied 2D primary ammonium dicarboxylate (PAD) supramolecular synthon in the context of supramolecular gelation. Single crystal structures of 9 out of 14 diprimary ammonium dicarboxylate (DPAD) salts were determined. The results showed that none of the salts displayed the expected 2D DPAD synthon; instead, all of them self-assembled into a 3D hydrogen-bonded network. Consequently, only two salts, namely, B3FA and B4SA, appeared to show gelation behavior producing weak gelsa finding that corroborated well with the current understanding of gelation.

■

INTRODUCTION The supramolecular synthon1 is a conceptual tool that is being successfully used in designing functional materials following the concept of crystal engineering.2 Like the synthon in the retrosynthesis involved in covalent organic synthesis,3 the supramolecular synthon plays the same pivotal role in designing and synthesizing supramolecular solids that might show the desired functional properties.4 Our group has been involved in exploiting the merit of the supramolecular synthon in the context of crystal engineering to develop new functional soft materials, such as supramolecular gels (SGs).5 When a hot solution of a small molecule is allowed to cool to room temperature, it is observed in suitable cases that the whole volume of the solution behaves like a solid, which can withstand its own weight against gravity. Such a solid-like mass is known as a gel, and if the gel is formed via supramolecular selfassembly involving the small molecule in the solution (gelator), it is known as a supramolecular gel, which are of current and contemporary interest in material science as such soft materials offer various potential applications starting from catalysis, optical devices to biomedical applications.6 We have been trying to probe the role of the supramolecular synthon in designing new supramolecular gels. Nearly a decade ago, Shinkai and co-workers proposed, based on a handful of crystal structures of some sugar-based molecules, that the 1D hydrogen-bonded network (HBN) promoted gelation, whereas 2D and 3D networks produced either a weak gel or no gelation at all.7 Our group, a few years later, provided the most conclusive evidence based on single crystal structures of quite a few gelators and a large number of nongelators in favor of © 2013 American Chemical Society

Shinkai’s proposition. Since then, we have reported a large number of supramolecular gels derived from low-molecularweight gelators (LMWGs) that were solely designed based on various supramolecular synthons. Thus, secondary ammonium monocarboxylate (SAM),8 its extension, namely, secondary ammonium dicarboxylate (SAD),9 primary ammonium monocarboxylate (PAM),10 and its extension, namely, primary ammonium dicarboxylate (PAD),11 synthons were successfully exploited to design a large number of LMWGs. Recently, we examined the supramolecular synthon transferability in diprimary ammonium moncarboxylate salts that we termed as the DPAM synthon and reported a number of supramolecular gels based on this synthon.12 Many such supramolecular gels reported by us displayed intriguing functional properties, such as selective gelation of oil from an oil/water mixture;8a,b,10a load-bearing, self-healing, and shape-retaining gels;8f and sustained release of pheromones,10d which might find application in pest control. Among these supramolecular synthons we have investigated thus far, the PAD synthon is quite intriguing. Though this synthon is generally a 2D synthon, it has a tendency to display hydrogen bond isomerism to produce a 1D nanotubular network induced by alkyl−alkyl hydrophobic interactions.13 Out of the 62 PAD salts that we have reported thus far, 37 (∼60%) of them were gelators. Out of the 15 crystal structures of these PAD salts, 12 of them displayed a 2D HBN of which 50% of the salts are gelators, Received: July 12, 2013 Revised: August 30, 2013 Published: August 30, 2013 4559

dx.doi.org/10.1021/cg401052a | Cryst. Growth Des. 2013, 13, 4559−4570

Crystal Growth & Design

Article

Scheme 1. Extending 1D PAD to 2D DPAD Synthon

whereas the rest showed a 1D HBN. Thus, the PAD synthon proves to be a reasonably good synthon for imparting gelation. With this background, we are now curious to see what would be the resulting HBN if we push the PAD synthon further, wherein a dicarboxylic acid is reacted with a diamine. If such a combination follows the similar HBN (i.e., frequently occurring 2D HBN) as observed in the PAD synthon, the resulting HBN in the new system, which we call hereafter diprimary ammonium dicarboxylate (DPAD), is expected to be 2D as well (Scheme 1). A CSD (CSD, version 1.15; CCDC: Cambridge, U.K., 2013) search revealed that such a 2D DPAD synthon did not exist in the various DPAD salts reported in the database (vide infra). Thus, we selected a series of dicarboxylic acids having aromatic and aliphatic backbones to react with two primary diamines, namely, 1,3-diamino propane and 1,4-diamino butane, in order to study the resulting HBN. We have systematically varied the dicarboxylic acid backbone while going from malonic to succinic to fumaric to maleic acids. We have also taken the aromatic rigid backbone, such as terephthalic acid and 2,6-naphthoic diacid. Finally, we also exploited a chiral diacid, such as L-tartaric acid (Scheme 2). This article describes the synthesis of a new series of DPAD salts and their characterization using FT-IR, 1H and 13C NMR, and elemental analysis. Single crystal structures of nine salts were investigated and discussed in the context of the supramolecular synthon; exclusively, all of them displayed a 3D HBN instead of a 2D HBN as envisaged. Only two salts, namely, B3SA and B4FA, displayed gelation ability with DMSO and aqueous DMSO, respectively.

Scheme 2. Various DPAD Salts Studied Herein

C2/c, whereas the rest of them crystallized in the centrosymmetric triclinic space group P1̅. Malonic Acid Salts. B3MNA. The X-ray quality single crystal was grown from a methanol−water solution of B3MNA salt (space group “P21/c”). In the asymmetric unit, one dicarboxylate and one diammonium species were located. The diammonium propane moiety displayed an anti−gauche conformation with the corresponding dihedral angles of 163.2° and 60.2°. The C−O distances [1.2354(19)− 1.2608(18) Å] of the acid moiety clearly indicated the complete deprotonation. In the crystal structure, each dicarboxylate anion was found to be involved in hydrogen bonding via N−H···O interactions [N···O = 2.7200(19)− 2.9998(19) Å; ∠N−H···O = 138.2−174.8°] with six neighboring diammonium cations. The HBN in the crystal structure may be visualized as the zigzag array of the ion pairs, which resulted in a 2D sheet sustained by N−H···O hydrogen bonding (Figure 1A). Further N−H···O interactions allowed the sheet structure to arrange in a parallel fashion, resulting in a 3D HBN (Figure 1B). Because we failed to grow suitable single

■

RESULTS AND DISCUSSION The salts were synthesized by reacting the corresponding acid and amine in a 1:1 molar ratio in MeOH. The absence of a stretching band at (1676−1742) cm−1 (for COOH) and the appearance of new band at (1589−1666) cm−1 (for COO−) in the FT-IR of the salts clearly indicated that both of the carboxylic acid moieties were deprotonated, indicating the formation of a 1:1 salt. The single crystals for X-ray diffraction were grown via slow evaporation in suitable solvents. Out of 14 salts, we were able to crystallize 9 salts (Table 1). Despite our serious efforts, we failed to grow X-ray quality single crystals for B3MA, B4MA, B4MNA, B3SA, and B4TA. Most of the crystals belonged to the centrosymmetric monoclinic space group P21/c along with a few in P21/n and 4560


4561

CCDC No. empirical formula formula weight crystal size/mm crystal system space group a/Å b/Å c/Å α/deg β/deg γ/deg volume/Å3 Z

crystal parameters

R indices (all data) B3TTA

B3MNA

937535 C12H18N2O4 254.28 0.65 × 0.32 × 0.06 triclinic P1̅ 8.215(5) 8.317(5) 9.662(5) 81.663(12) 78.055(12) 88.794(12) 639.0(6) 2

937541 C6H14N2O4 178.19 0.5 × 0.33 × 0.16 monoclinic P21/c 9.8723(17) 8.8608(16) 10.2369(18) 90.00 94.977(4)) 90.00 892.1(3) 4 1.327 384 0.111 298(2) 0.0209 −11/10, −10/10, −12/12 2.07/25.00 9158/1572/1446 1572/0/111 1.137 R1 = 0.0369 wR2 = 0.1227 R1 = 0.0407 wR2 = 0.1368 B4TTA

937540 C11H20N2O6 276.29 0.552 × 0.216 × 0.053 monoclinic P21/n 8.1716(16) 15.687(3) 10.504(2) 90.00 94.178(5) 90.00 1342.9(4) 4

CCDC No. empirical formula formula weight crystal size/mm crystal system space group a/Å b/Å c/Å α/deg β/deg γ/deg volume/Å3 Z Dcalc/g cm−3 F(000) μ Mo Kα/mm−1 temp/K Rint range of h, k, l θ min/max/deg reflections collected/unique/observed [I > 2σ(I)] data/restraints/parameters goodness of fit on F2 Final R indices [I > 2σ(I)]

crystal parameters

Table 1. Crystallographic Parameters B4SA

937542 C15H18N2O4 290.31 0.65 × 0.28 × 0.05 monoclinic P21/n 13.372(3) 8.4957(17) 13.943(3) 90.00 117.316(4) 90.00 1407.3(5) 4

937538 C8H18N2O4 206.24 0.36 × 0.24 × 0.08 monoclinic P21/c 5.6014(7) 11.0184(14) 8.3208(11) 90.00 101.462(4) 90.00 503.31(11) 2 1.361 224 0.108 100(2) 0.0627 −6/6, −12/13, −9/9 3.11/24.98 5647/882/808 882/0/65 1.091 R1 = 0.0359 wR2 = 0.0913 R1 = 0.0389 wR2 = 0.0955 B3NDA

B3FA

937536 C16H20N2O4 304.34 0.25 × 0.11 × 0.04 monoclinic C2/c 16.151(3) 10.551(2) 9.536(2) 90.00 113.274(4) 90.00 1492.8(6) 4

937543 C7H14N2O4 190.20 0.50 × 0.43 × 0.29 monoclinic P21/c 8.0771(19) 15.649(4) 7.9624(19) 90.00 110.54(4) 90.00 942.4(4) 4 1.341 408 0.110 298(2) 0.0203 −9/9, −18/18, −9/9 2.60/25.00 8692/1660/1559 1660/0/120 1.049 R1 = 0.0353 wR2 = 0.0955 R1 = 0.0372 wR2 = 0.0979 B4NDA

B4FA

937539 C14H32N4O12 448.44 0.5 × 0.44 × 0.24 monoclinic P21 9.4324(4) 8.7515(4) 12.4444(6) 90.00 102.0730910) 90.00 1004.53(8) 2

937537 C8H16N2O4 204.23 0.50 × 0.35 × 0.16 triclinic P1̅ 5.0550(9) 5.5332(10) 9.1088(16) 78.104(4) 89.826(4) 82.836(3) 247.29(8) 1 1.371 110 0.110 298(2) 0.0167 −6/5, −6/6, −10/10 2.29/25.00 2347/872/807 872/0/65 1.143 R1 = 0.0322 wR2 = 0.0930 R1 = 0.0340 wR2 = 0.0951 B3TA

Crystal Growth & Design Article


1.483 480 0.129 120(2) 0.0179 −11/10, −10/10, −14/14 1.67/25.00 9454/1901/1885 1901/1/274 1.106 R1 = 0.0404 wR2 = 0.1240 R1 = 0.0406 wR2 = 0.1242 R indices (all data)

B4NDA

1.354 648 0.098 298(2) 0.0559 −15/14, −10/10, −9/9 2.75/20.17 5080/713/530 713/0/101 1.130 R1 = 0.0662 wR2 = 0.1848 R1 = 0.0897 wR2 = 0.2067 1.370 616 0.100 298(2) 0.0410 −16/16, −10/10, −17/17 1.75/26.70 14 674/2964/2104 2964/0/192 1.035 R1 = 0.0875 wR2 = 0.2497 R1 = 0.1159 wR2 = 0.2742

B3NDA

crystals of B4MNA, we were unable to study the various hydrogen bonding present in its crystalline form. Succinic Acid Salts. B4SA. This salt was crystallized from methanol−water (space group “P21/c”). The asymmetric unit contained half of the 1,4-diammonium butane and half of the succinate moiety. 1,4-Diammonium butane showed an anti− anti conformation having dihedral angles of 176.6° and 180°. The complete deprotonation was supported by the C−O distance [1.2515(16)−1.2649(16) Å] of the carboxylate. Each dicarboxylate anion participated in hydrogen bonding with eight adjacent ammonium cations via N−H···O interactions [N···O = 2.7589(14)−2.7935(14) Å; ∠N−H···O = 163.7− 165.3°]. The HBN may be best described as a 3D array of 2D hydrogen-bonded corrugated sheets sustained by N−H···O interactions (Figure 2). The salt B3SA could not be studied because we failed to crystallize X-ray quality single crystals. Fumaric Acid Salts. B3FA. The salt B3FA was crystallized from water (space group “P21/c”). The asymmetric unit contained one 1,3-diammonium propane and two fumarate moieties both located on an inversion center. The 1,3diammonium propane displayed an anti−anti conformation having dihedral angles of 179.4° and 179.0°. The C−O distance [1.2368(16)−1.2636(16) Å] supported the complete deprotonation of the fumaric acid. Each dicarboxylate was attached with six neighboring ammonium cations via N−H···O interactions [N···O = 2.7312(15)−2.8046(15) Å; ∠N−H···O = 156.1− 178.1°]. The overall hydrogen-bonding network may be described as alternating layers of crystallographically independent acid moieties pillared by diammonium cations sustained by N−H···O interactions (Figure 3A). B4FA. The salt B4FA was crystallized from diethylene glycol−methanol−water (space group “P1̅”), and the asymmetric unit contained one 1,4-diammonium butane and one fumarate moiety. The 1,4-diammonium butane displayed an allanti conformation having dihedral angles of 179.5° and 180.0°. The C−O distance (1.2559(16)−1.2453(16) Å) indicated the complete deprotonation. It was found that each dicarboxylate anion was involved in N−H···O hydrogen bonding interactions [N···O = 2.7590(16)−2.9757(17) Å; ∠N−H···O = 147.9− 170.6°] with eight neighboring ammonium cations. The 2D hydrogen-bonded sheet architecture could be seen in the crystal structure, which was further packed in a parallel fashion sustained by N−H···O interactions (Figure 3B). Terephthalic Acid Salts. B3TTA. It was crystallized from DMSO−water (space group “P21/n”). The asymmetric unit contained one 1,3-diammonium propane (cation), one terephthalate (anion) moiety and two solvate water molecules. The 1,3-diammonium propane displayed an all-anti conformation having dihedral angles of 176.7° and 175.2°. The C−O distance [1.2477(17)−1.267(3) Å] confirmed the complete deprotonation of the acid moieties. In the crystal structure, each dicarboxylate anion was involved in charged-assisted hydrogen bonding with four neighboring ammonium cations and four lattice occluded water molecules sustained by N−H···O interactions [N···O = 2.692(3)−2.971(3) Å; ∠N−H···O = 172(3)−162(3)°] and ∠O−H···O [O···O = 2.869(3)− 2.681(3) Å; ∠O−H···O = 172(3)−161(3)°]. The hydrogenbonded network may be described as 1D arrays of terephthalates pillared by diammonium cations; such arrays were packed in a parallel fashion sustained by both N−H···O interactions. The solvate water molecules were held via O−H··· O interactions within the interstitial space of such parallely packed 1D arrays, resulting in an overall 3D HBN (Figure 4A).

1.322 272 0.100 100(2) 0.0202 −9/9, −9/9, −11/11 2.18/25.00 5973/2221/2011 2221/0/165 1.047 R1 = 0.0351 wR2 = 0.1012 R1 = 0.0384 wR2 = 0.1050

B4TTA

Article

1.367 592 0.111 298(2) 0.0532 −9/9, −17/17, −11/11 2.34/23.88 11 225/2074/150 1520/0/252 0.934 R1 = 0.0474 wR2 = 0.1281 R1 = 0.0667 wR2 = 0.1442

B3TTA crystal parameters

Table 1. continued

Dcalc/g cm−3 F(000) μ Mo Kα/mm−1 temp/K Rint range of h, k, l θ min/max/deg reflections collected/uniqe/observed [I > 2σ(I)] data/restraints/parameters goodness of fit on F2 final R indices [I > 2σ(I)]

B3TA


4562



Article

Figure 1. (A) 2D hydrogen-bonded sheet and (B) its parallel packing leading to a 3D HBN in B3MNA. Cationic and anionic backbones are shown in magenta and orange, respectively; dotted lines (cyan) present the HBN.

B4TTA. The salt B4TTA was crystallized from DMF−water (space group “P1”̅ ). The asymmetric unit contained two 1,4diammonium butane (cation) both located on an inversion center and one terephthalate (anion) moiety. The 1,4diammonium propane displayed an all-anti conformation having dihedral angles of 172.2, 180, and 176.6°. The complete deprotonation was confirmed from the C−O distance [1.2477(17)−1.2702(17) Å]. Each dicarboxylate anion was involved in charged-assisted hydrogen bonding with six neighboring ammonium cations sustained by N−H···O interactions [N···O = 2.7212(19)−2.772(2) Å; ∠N−H···O = 158.3−173.6°]. The relative orientation of the diammonium species in the crystal structure was almost orthogonal to each other. As a result, the dianionic species and one of the cations formed a 2D sheet that was arranged in a parallel fashion pillared by the other cationall sustained in N−H···O hydrogen bonding (Figure 4B). 2,6-Naphthoic Diacid Salts. B3NDA. The salt B3NDA was crystallized from DMF−water (space group “P21/n”). The asymmetric unit contained one 1,3-diammonium propane (cation) and one 2,6-naphthoic diacetate (anion). The 1,3-

diammonium propane displayed an anti−anti conformation having dihedral angles of 178.1° and 178.4°. Here, also the complete deprotonation was confirmed from the C−O distance (1.236(4)−1.261(4) Å). Each dicarboxylate anion is involved in charged-assisted hydrogen bonding with seven neighboring ammonium cations sustained by N−H···O interactions [N···O = 2.710(4)−2.947(4) Å; ∠N−H···O = 154.6−170.2°]. The relative orientation of the cation and anion was found to be almost orthogonal, and the hydrogen-bonding network may be visualized as a 1D array of dicarboxylate moieties pillared by the diammonium cations; such 1D arrays were packed in a parallel fashion sustained by N−H···O interactions, leading to an overall 3D HBN (Figure 5A). The naphthyl moieties displayed π−π stacking interactions (centroid−centroid = 3.701 Å) within the 1D array. B4NDA. The salt B4NDA was crystallized from DMF−water (space group “P2/c”). The asymmetric unit was occupied by one 1,4-diammonium butane and one 2,6-naphthoic diacetate moiety. The 1,4-diammonium butane displayed an all-anti conformation having dihedral angles of 159.5° and 173.4°. The C−O distance (1.249(6)−1.250(6) Å) confirmed the complete 4563



Article

alternatively to form 1D hydrogen-bonded chains that further self-assembled into a 3D network. However, the other salt B4TTA displayed a different HBN, wherein the dications took up a mutually orthogonal arrangement. Unfortunately, the crystals of B4MNA, B3SA, and B4TA could not be grown, and therefore, we could not compare the effect of the anionic and cationic backbones on the resultant crystal structures. The most important observation, however, was the absence of the desired 2D HBN envisaged as the extension of the 2D PAD synthon (Scheme 1). At this stage, we carried out a CSD search (CSD, version 1.15; CCDC: Cambridge, U.K., 2013) to find out whether the DPAD 2D synthon indeed existed or not in this class of organic salts. Thus, a search with “diammonium” as the keyword revealed that there was no report of DPAD salt containing 1,3-diammonium propane, whereas there were only two structures containing 1,4-diammonium butane (Refcode: TOHGOM14a and VIGRUY14b). Whereas TOHGOM was found to be a 2:1 salt of malonic acid and 1,4-diaminobutane, VIGRUY was a 1:1 salt of terephthalic acid and 1,4diaminobutane having an identical space group and a near identical cell dimension of B4TTA; the only difference was that the data collected for VIGRUY were at room temperature, whereas, for B4TTA, they were low-temperatrue (100 K) data. We also carried out a CSD search having individual dicarboxylates used in this study as the search fragment, and none of them resulted in a relevant hit containing diprimary ammonium cation, except in the case of fumaric acid, wherein a DPAD salt hydrate having a diprimary ammonium cation with an ether backbone was reported (Refcode: XELJED14c). Thus, the DPAD 2D synthon as an extension of the 2D PAD synthon did not exist in the similar class of organic salts. It may be noted here that, in order to form either the 2D PAD or the 2D DPAD synthon, the ion pairs must be arranged in a parallel fashion and should lie on the same plane (Scheme 1); while it is true for the 2D PAD synthon, as demonstrated in several stuctures (see the Introduction), it appears important for the cations and anions to arrange in a different fashion in DPAD salts, resulting in a 3D HBN in the presently studied DPAD salts. It is clear from the SXRD data that none of the crystals belonged to the desired 2D DPAD synthon as envisaged. Thus, we were curious to know the gelation behavior of these salts. As expected, gelation tests with 14 different solvents produced no gels except two weak gels of B3SA and B4FA (Table S10, Supporting Information); these two salts appeared to have immobilized (gelled) DMSO and DMSO/water, respectively. The MGC of the two salts were found to be 4 and 2.2 wt %, respectively. Both the gels were unstable, precipitating out within a few hours. The TEM image for the DMSO gel showed a typical fibrous morphology, whereas both SEM and TEM images of DMSO/water displayed a leaf kind of morphology (Figure 7). Differential scanning calorimetry did not show any significant phase transition (Figure S10, Supporting Information). Frequency sweep experiments in dynamic rheology, wherein the elastic modulus (G′) and loss modulus (G′′) are plotted against angular frequency ω with a constant applied strain of 0.1%, produced nontypical plots; for a viscoelastic material, such as gel, G′ should be larger than G′′ and they should be frequency invariant over a long time period. However, for the DMSO gel of B3SA, it showed a steady decline of both G′ and G′′ with frequency, meaning that it probably was not a strong viscoelastic material (Figure 8). For the other gel (B4FA), both

Figure 2. 3D array of 2D hydrogen-bonded corrugated sheets of B4SA sustained by N−H···O interactions. Cationic and anionic backbones are shown in magenta and orange, respectively; dotted lines (cyan) present the HBN.

deprotonation of the acid moieties. Each dicarboxylate anion was involved in charged-assisted hydrogen bonding sustained by N−H···O interactions [N···O = 2.732(6)−2.946(5) Å; ∠N−H···O = 142.8−166.5°] with six neighboring ammonium cations. The alternative arrangement of hydrogen-bonded dicarboxylates and the diammonium cation resulted in a 2D sheet like the HBN, which were further packed in a parallel fashion sustained by N−H···O interactions, resulting in an overall 3D HBN (Figure 5B). However, the naphthyl moieties did not show any π−π stacking interactions. Tartaric Acid Salts. B3TA. It was crystallized from DMF− water (space group “P21”), and its asymmetric unit contained two pairs of L-tartarate and 1,3-diammonium propane, of which one cation was found to be disordered. One of the two 1,3diammonium propane showed an anti−gauch conformation having dihedral angles of 160.6° and 75.0°, whereas the conformation of the other one could not be established because of its disordered nature. The complete deprotonation of the acid was confirmed from the C−O distance [1.233(4)− 1.268(4) Å] of the acid moiety. Extensive hydrogen-bonding interactions of type N−H···O [N···O = 2.737(3)−2.939(3) Å; ∠N−H···O = 138.5−167.2°] and O−H···O [O···H = 2.661(3)−2.845(3) Å; ∠O−H···O = 160.5−174.4°] ultimately lead to the formation of a 3D HBN (Figure 6). The salt B4TA could not be studied due to the lack of X-ray quality single crystal. Thus, careful analyses of the foregoing discussions on single crystal structures revealed interesting observations. The salts of 1,3-diaminopropane with acids having a rigid backbone, namely, B3FA, B3NDA, and B3TTA, showed an HBN, wherein the dications acted as pillars to assemble the parallely arranged acid moieties. Interestingly, even the hydrogen bonding capable water molecules as guests in B3TTA could not influence the overall HBN. The fact that the chain length of the dication is crucial in shaping up of the resultant HBN in these salts was evident from the completely different types of HBN observed in the corresponding salts having one extra methylene group in the dication, namely, B4SA, B4FA, and B4NDA; in these structures, the dianions and the dications were arranged 4564



Article

Figure 3. 3D HBN in (A) B3FA and (B) B4FA. Cationic and anionic backbones are shown in magenta and orange, respectively; dotted lines (cyan) present the HBN.

G′ and G′′ were found to be highly fluctuating, indicating the nongel characteristics of the material.

B4NDA, showed a 1D alternating array of cations and anions that further self-assembled into a 3D network. Subsequent gelation studies with various solvents revealed that none of these salts were gelators, except the salts B3SA and B4FA. However, DSC and rheological studies indicated that they were not truly viscoelastic materials or gels. These results once again clearly supported the working hypothesisthe 1D HBN promoted gelation, whereas 2D and 3D HBNs either produced weak gels or promoted no gelation at all.

■

CONCLUSION Thus, on the basis of the supramolecular synthon approach toward designing LMWGs, we explored a new series of DPAD salts and characterized a majority of them (9 out of 14 salts) by single-crystal X-ray diffraction. Table 2 summarizes the overall findings. Careful analyses of the SXRD data revealed that the resultant HBN was not the 2D DPAD synthon as envisaged; instead, all of them showed a 3D HBN. Nonplanar packing of the ion pairs seemed to have prevented the formation of the expected 2D DPAD synthon, which was a logical extension of the 2D PAD synthon. The subtle change in methylene group in the cationic counterpart of the salts appeared to have a profound effect on the resultant HBN; thus, the salts B3FA, B3NDA, and B3TTA displayed the cationic counterpart as pillars, whereas the higher analogues, namely, B4SA, B4FA, and

■

EXPERIMENTAL SECTION

Materials and Methods. All the reagents were obtained from various commercial sources and used without further purification. Solvents were of L. R. grade and used without further distillation. All the IR spectra were obtained on an FT-IR instrument (FTIR-8300, Shimadzu) using KBr pallets. The elemental compositions of the purified compounds were confirmed by elemental analysis (PerkinElmer Precisely, Series-II, CHNO/S Analyzer-2400). Both 1H and 4565



Article

Figure 4. (A) Overall 3D HBN of B3TTA made by interconnections of 1D arrays of terephthalates pillared by diammonium cations; lattice occluded water molecules shown in green. (B) The overall 3D HBN of B4TTA generated by interconnection of 2D pillared sheets. Cationic and anionic backbones are shown in magenta and orange, respectively; dotted lines (cyan) present the HBN. 13

acid solutions; the salts were precipitated out and collected by filtration. Some diacids were not soluble in mthanol even after heating, but they became soluble immediately after addition of diamine. Some salts did not precipitate out; those salts were collected by evaporating the solvent. The salt formation was confirmed by FT-IR, 1H and 13C NMR, and CHN analysis and single-crystal X-ray diffraction in a few cases. Single-crystal X-ray diffraction data were collected using Mo Kα (λ = 0.7107 Å) radiation on a BRUKER APEX II diffractometer equipped with CCD area detector. Data collection, data reduction, and structure solution/refinement were carried out using the software package of SMART APEX. All structures were solved by the direct method and

C NMR were performed on a 400 MHz spectrometer (Bruker Ascend 400) and a 500 MHz spectrometer (Bruker Ultrasheild Plus500). For all the NMR data collection, standard 5 mm NMR tubes were used. The chemical shifts (δ) are reported here in parts per million (ppm) relative to D2O residual solvent peaks. All the TEM were recorded using a JEOL instrument with a carbon-coated 300 mesh copper TEM grid at 200 kV. Scanning electron microscopy (SEM) was recorded in a JEOL, JMS-6700F, field emission scanning electro microscope. Differential scanning calorimetry (DSC) was recorded in a PerkinElmer, Diamond DSC. Rheology studies were carried out using an SDT Q series advanced rheometer-AR 2000. The diacids were taken in the beakers and dissolved in methanol. One equivalent of the corresponding diamines were then added to the 4566



Article

Figure 5. (A) Parallel packing of 1D hydrogen-bonded array of the ion pair sustained by N−H···O interactions in B3NDA. (B) Parallel packing of the 2D sheets of the ion pairs reinforced by N−H···O interactions in B4NDA. Cationic and anionic backbones are shown in magenta and orange, respectively; dotted lines (cyan) present the HBN. B3SA. mp = 174−178 °C. Elemental analysis calcd for C7H16N2O4.H2O (%): C 39.99, H 8.63, N 13.33. Found: C 40.24, H 8.74, N 13.36. 1H NMR (500 MHz, D2O): δ (ppm) = 3.10−2.96 (t, J = 8.0 Hz, 4H); 2.28 (s, 4H); 1.99−1.91 (m, 2H). 13C NMR (400 MHz, D2O): δ (ppm) = 182.55, 36.77, 34.32 and 25.08. FT-IR (KBr pellet): 3269, 3211, 2976, 2901, 2837, 2804, 2582, 2517, 1666, 1562, 1481, 1393, 1227, 1180, 1018, 997, 972, 960, 920, 816, 771, 663, 636, 606, 586, and 554 cm−1. B4SA. mp = 204−205 °C. Elemental analysis calcd for C8H18N2O4 (%): C 46.59, H 8.80, N 13.58. Found: C 45.23, H 8.46, N 13.27. 1H NMR (500 MHz, D2O): δ (ppm) = 2.91 (s, 4H); 2.27 (s, 4H); 1.63 (s, 4H). 13C NMR (400 MHz, D2O): δ (ppm) = 182.50, 38.99, 34.36 and 24.05. FT-IR (KBr pellet): 3163, 3013, 2972, 2934, 2855, 2806, 2745, 2641, 2504, 1661, 1634, 1560, 1504, 1470, 1418, 1381, 1337, 1304, 1248, 1231, 1171, 1136, 1069, 1028, 916, 870, 810, 746, 658, 617, 581, 529, and 459 cm−1. B3FA. mp = 210−215 °C. Elemental analysis calcd for C7H14N2O4 (%): C 44.20, H 7.42, N 14.73. Found: C 44.40, H 6.61, N 14.88. 1H NMR (400 MHz, D2O): δ (ppm) = 6.39 (s, 2H); 2.98−2.94 (t, J = 8.0 Hz, 4H); 1.98−1.89 (m, 2H). 13C NMR (500 MHz, D2O): δ (ppm) =

refined in a routine manner. Non-hydrogen atoms were treated anisotropically. B3MNA. The melting point could not be determined due to the highly hygroscopic nature of the salt. Elemental analysis calcd for C6H14N2O4 (%): C 40.44, H 7.92, N 15.72. Found: C 39.86, H 8.70, N 15.44. 1H NMR (500 MHz, D2O): δ (ppm) = 2.98−2.90 (m, 6H); 1.95−1.87(m, 2H). 13C NMR (400 MHz, D2O): δ (ppm) = 177.53, 36.77 and 25.08. FT-IR (KBr pellet): 3389, 3072, 2908, 2835, 1639, 1566, 1475, 1462, 1439, 1408, 1352, 1259, 1206, 1184, 1117, 1086, 982, 928, 885, 845, 820, 775, 704, 623, 588, 507, and 424 cm−1. B4MNA. The melting point could not be determined due to the highly hygroscopic nature of the salt. Elemental analysis calcd for C7H16N2O4 (%): C 43.74, H 8.39, N 14.57. Found: C 24.27, H 8.26, N 13.98. 1H NMR (500 MHz, DMSO-D6): δ (ppm) = 2.95−2.92(m, 4H); 1.67−1.63 (m, 4H). 13C NMR (400 MHz, D2O): δ (ppm) = 177.48, 38.98 and 24.01. FT-IR (KBr pellet): 3026, 2951, 2891, 2876, 2822, 2697, 2523, 1634, 1556, 1435, 1396, 1350, 1281, 1252, 1221, 1171, 1126, 1109, 1038, 997, 928, 903, 820, 764, 744, 700, 619, 584, and 517 cm−1. 4567



Article

MHz, D2O): δ (ppm) = 175.45, 130.62, 39.11 and 24.42. FT-IR (KBr pellet): 3373, 3269, 3042, 2969, 2872, 1652, 1605, 1557, 1505, 1472, 1427, 1393, 1341, 1333, 1306, 1285, 1263, 1233, 1175, 1165, 1134, 1107, 1042, 1018, 972, 889, 881, 854, 802, 785, 752, 710, 652, 621, 579, 552, 527, 461, and 438 cm−1. B3TTA. mp = 252−254 °C. Elemental analysis calcd for C11H16N2O4 (%): C 54.99, H 6.71, N 11.66. Found: C 54.57, H 7.03, N 11.38. 1H NMR (500 MHz, D2O): δ (ppm) = 7.76−7.72 (m, 4H); 2.96−2.87 (m, 4H); 1.95−1.84 (m, 2H). 13C NMR (500 MHz, D2O): δ (ppm) = 175.37, 138.83, 128.71, 38.70, 25.00. FT-IR (KBr pellet): 3057, 2984, 2895, 2818, 2795, 2748, 2675, 2623, 2540, 2475, 1661, 1620, 1574, 1529, 1510, 1495, 1454, 1406, 1387, 1358, 1335, 1304, 1232, 1204, 1161, 1140, 1119, 1086, 1014, 991, 951, 882, 836, 812, 766, 746, 555, 501, 444, and 412 cm−1. B4TTA. mp = 255−262 °C. Elemental analysis calcd for C12H18N2O4 (%): C 56.68, H 7.13, N 11.02. Found: C 55.97, H 6.85, N 10.88. 1H NMR (500 MHz, D2O): δ (ppm) = 7.77−7.70 (d, J = 15 Hz, 4H); 2.94−2.70 (m, 4H); 1.64−1.42 (m, 4H). 13C NMR (500 MHz, D2O): δ (ppm) = 175.31, 138.86, 128.73, 38.94, 24.00. FT-IR (KBr pellet): 2953, 2897, 2834, 2764, 2635, 2567, 1634, 1568, 1497, 1437, 1433, 1377, 1358, 1331, 1316, 1294, 1275, 1161, 1109, 1086, 1051, 1040, 1013, 949, 882, 816, 741, 523, and 503 cm−1. B3NDA. mp > 275 °C. Elemental analysis calcd for C15H18N2O4 (%): C 62.06, H 6.25, N 9.65. Found: C 60.74, H 6.09, N 9.30. 1H NMR (400 MHz, D2O): δ (ppm) = 8.25 (s, 2H); 7.89−7.84 (d, J = 8.4, 2H); 7.84−7.79 (d, J = 8.4, 2H); 2.81−2.77 (t, J = 8.0 Hz, 4H); 1.95−1.85 (m, 2H). 13C NMR (500 MHz, D2O): δ (ppm) = 175.41, 135.08, 133.69, 128.96, 126.13, 36.60 and 24.92. FT-IR (KBr pellet): 3167, 2980, 2814, 2724, 2656, 2594, 2536, 1634, 1601, 1572, 1543, 1530, 1505, 1493, 1474, 1451, 1385, 1352, 1335, 1231, 1213, 1196, 1186, 1136, 1105, 1092, 1065, 997, 963, 937, 909, 843, 785, 773, 640, 552, 476, 465, and 438 cm−1. B4NDA. mp > 275 °C. Elemental analysis calcd for C16H20N2O4 (%): C 63.14, H 6.62, N 9.20. Found: C 63.21, H 6.03, N 8.64. 1H NMR (400 MHz, D2O): δ (ppm) = 8.28 (s, 2H); 7.91−7.88 (d, J = 8.4, 2H); 7.86−7.82 (d, J = 8.4, 2H); 2.81−2.77 (m, 4H); 1.58−1.48 (m, 4H). 13C NMR (500 MHz, D2O): δ (ppm) = 175.40, 135.15, 133.72, 128.98, 128.78, 126.17, 38.79 and 23.86. FT-IR (KBr pellet): 3026, 3011, 2951, 2891, 2822, 2697, 2631, 2523, 1632, 1603, 1586, 1570, 1553, 1537, 1516, 1501, 1483, 1393, 1375, 1354, 1325, 1271, 1236, 1186, 1136, 1096, 1078, 1044, 1022, 972, 912, 895, 840, 835, 797, 783, 748, 509, 480, and 422 cm−1. B3TA. mp = 202−206 °C. Elemental analysis calcd for C7H16N2O6 (%): C 37.50, H 7.19, N 12.49. Found: C 37.59, H 7.10, N 12.48. 1H NMR (500 MHz, D2O): δ (ppm) = 4.23 (s, 2H); 3.00−2.98 (t, J = 10 Hz, 4H); 2.03−1.93 (m, 2H). 13C NMR (400 MHz, D2O): δ (ppm) = 178.60, 74.03, 36.75 and 25.03. FT-IR (KBr pellet): 3433, 3163, 3044, 2903, 2834, 1648, 1628, 1604, 1570, 1551, 1518, 1501, 1481, 1468, 1449, 1410, 1308, 1252, 1204, 1117, 1072, 978, 764, 714, 625, and 457 cm−1. B4TA. mp = 195−199 °C. Elemental analysis calcd for C8H18N2O6 (%): C 40.33, H 7.62, N 11.76. Found: C 39.36, H 7.47, N 11.34. 1H

Figure 6. 3D HBN of B3TA. Cationic and anionic backbones are shown in magenta and orange, respectively; dotted lines (cyan) present the HBN. 174.62, 135.36, 36.58 and 24.87. FT-IR (KBr pellet): 3001, 2938, 2895, 2835, 2762, 2700, 2610, 2550, 1661, 1634, 1574, 1559, 1539, 1505, 1478, 1458, 1360, 1329, 1308, 1238, 1215, 1190, 1148, 1055, 1040, 999, 972, 953, 845, 806, 762, 669, 569, 550, 467, and 422 cm−1. B4FA. mp = 225−232 °C. Elemental analysis calcd for C8H16N2O4 (%): C 47.05, H 7.90, N 13.72. Found: C 47.14, H 7.77, N 13.68. 1H NMR (400 MHz, D2O): δ (ppm) = 6.40 (s, 2H); 2.91(s, 4H); 1.62 (s, 4H). 13C NMR (500 MHz, D2O): δ (ppm) = 174.77, 135.51, 38.99 and 24.05. FT-IR (KBr pellet): 3156, 307, 2960, 2878, 2799, 2629, 2592, 2548, 2506, 1657, 1566, 1526, 1466, 1381, 1358, 1335, 1302, 1281, 1246, 1211, 1126, 1041, 999, 951, 872, 806, 741, 673, 573, and 457 cm−1. B3MA. The melting point could not be determined due to the highly hygroscopic nature of the salt. Elemental analysis calcd for C7H14N2O4 (%): C 44.20, H 7.42, N 14.73. Found: C 42.11, H 7.42, N 14.38. 1H NMR (500 MHz, D2O): δ (ppm) = 5.95−5.65 (m, 2H); 3.25−3.10 (m, 1H); 3.10−2.75 (m, 4H); 2.00−1.95(m, 2H). 13C NMR (400 MHz, D2O): δ (ppm) = 175.25, 130.63, 36.25 and 24.96. FT-IR (KBr pellet): 3433, 3390, 3034, 3015, 2972, 2910, 2829, 1620, 1597, 1475, 1389, 1335, 1315, 1310, 1267, 1213, 1188, 1076, 1053, 970, 891, 864, 829, 756, 663, 569, and 511 cm−1. B4MA. mp = 188−192 °C. Elemental analysis calcd for C8H16N2O4.H2O (%): C 43.24, H 8.16, N 12.61. Found: C 43.40, H 7.82, N 12.55. 1H NMR (500 MHz, D2O): δ (ppm) = 5.92−5.88 (t, J = 3.5 Hz, 2H); 2.95−2.87 (m, 4H); 1.67−1.59 (m, 4H). 13C NMR (500

Figure 7. (A) SEM image of B4FA, (B) TEM image of B4FA, and (C) TEM image of B3SA displaying in the corresponding xerogel. 4568



Article

Figure 8. Dynamic frequency sweep experiments in rheological measurements of 6 wt % DMSO gel of B3SA and 6 wt % DMSO−water gel of B4FA with a constant strain of 0.1% displaying nonviscoelastic behavior of the samples.

Table 2. Summary of the Overall Findings crystallization experiment compounds

solvent

crystal system

space group

results on gellation

type of HBN

B3MNA B4MNA B3SA B4SA B3FA B4FA B3MA B4MA B3TTA B4TTA B3NDA B4NDA B3TA B4TA

methanol−water no crystal obtained no crystal obtained methanol−water water diethylene glycol−methanol−water no crystal obtained no crystal obtained DMSO−water DMF−water DMF−water DMF−water DMF−water no crystal obtained

monoclinic

“P21/c”

nonpillared 3D HBN

monoclinic monoclinic triclinic

“P21/c” “P21/c” “P1̅”

monoclinic triclinic monoclinic monoclinic monoclinic

“P21/n” “P1”̅ “P21/n” “P2/c” “P21”

nongelator nongelator gelator nongelator nongelator gelator nongelator nongelator nongelator nongelator nongelator nongelator nongelator nongelator

■

NMR (500 MHz, D2O): δ (ppm) = 4.24 (s, 2H); 2.99−2.93 (m, 4H); 1.70−1.63 (m, 4H). 13C NMR (400 MHz, D2O): δ (ppm) = 178.60, 74.04, 39.01 and 24.03. FT-IR (KBr pellet): 3337, 3067, 3011, 2934, 2876, 1589, 1468, 1447, 1422, 1398, 1339, 1323, 1283, 1215, 1111, 1072, 1024, 993, 916, 872, 851, 760, 704, 596, 527, and 496 cm−1.

■

pillared 3D nonpillared pillared 3D nonpillared nonpillared

HBN 3D HBN HBN 3D HBN 3D HBN

REFERENCES

(1) Desiraju, G. R. Angew. Chem, Int. Ed. Engl. 1995, 34, 2311. (2) Desiraju, G. R.; Vittal, J. J.; Ramanan, A. Crystal Engineering: A Textbook; World Scientific, IISc Press: Singapore, 2011. (3) Corey, E. J. Pure Appl. Chem. 1967, 14, 19. (4) (a) Desiraju, G. R. J. Mol. Struct. 2003, 656, 5. (b) Desiraju, G. R. Angew. Chem., Int. Ed. 2007, 46, 8342. (5) Dastidar, P. Chem. Soc. Rev. 2008, 37, 2699. (6) (a) Escuder, B.; Llansola, F. R.; Miravet, J. F. New J. Chem. 2010, 34, 1044. (b) Kato, T. Science 2002, 295, 2414. (c) Ajayaghosh, A.; Praveen, V. K.; Vijayakumar, C.; George, S. J. Angew. Chem., Int. Ed. 2007, 46, 6260. (d) Lee, K. Y.; Mooney, D. J. Chem. Rev. 2001, 101, 1869. (e) Yang, Z.; Liang, G.; Ma, M.; Abbah, A. S.; Lu, W. W.; Xu, B. Chem. Commun. 2007, 843. (f) Gu, H.; Xu, K.; Yang, Z.; Changa, C. K.; Xu, B. Chem. Commun. 2005, 4270. (g) Zourob, M.; Gough, J. E.; Ulijn, R. V. Adv. Mater. 2006, 18, 655. (h) Zhou, M.; Smith, A. M.; Das, A. K.; Hodson, N. W.; Collins, R. F.; Ulijn, R. V.; Gough, J. E. Biomaterials 2009, 30, 2523. (i) Kumar, A.; Vemula, P. K.; Ajayan, P. M.; John, G. Nat. Mater. 2008, 7, 236. (j) Vemula, P. K.; Li, J.; John, G. J. Am. Chem. Soc. 2006, 128, 8932. (k) Gao, J.; Gu, H.; Xu, B. Acc. Chem. Res. 2009, 42, 1097. (l) Das, D.; Kar, T.; Das, P. K. Soft Matter 2012, 8, 2348. (m) Carretti, E.; Dei, L. In Molecular Gels. Materials with Self-Assembled Fibrillar Networks; Weiss, R. G., Terech, P., Eds.; Springer: Dordrecht,The Netherlands, 2005. (n) Jenning, V.; Gysler, A.; Schafer-Korting, M.; Gohla, S. H. Eur. J. Pharm. Biopharm. 2000, 49, 211. (o) Wynne, A.; Whitefield, M.; Dixon, A. J.; Anderson, S. J Dermatol. Treat. 2002, 13, 61. (p) Lloyd, G. O.; Steed, J. W. Nat. Chem. 2009, 1, 437. (q) Nakano, K.; Hishikawa, Y.; Sada, K.; Miyata, M.; Hanabusa, K. Chem. Lett. 2000, 29, 1170. (r) Terech, P.; Weiss, R. G. Chem. Rev. 1997, 97, 3133. (s) Kimura, M.; Kobayashi, S.; Kuroda,

ASSOCIATED CONTENT

S Supporting Information *

Molecular plot, hydrogen-bonding parameters, CIF, and gelation data table. This material is available free of charge via the Internet at http://pubs.acs.org.

■

nonpillared 3D HBN pillared 3D HBN nonpillared 3D HBN

AUTHOR INFORMATION

Corresponding Author

*Fax: +91-33-2473 2805. Tel: +91-33-2473 4971/5374/3073. E-mail: [email protected], parthod123@rediffmail.com. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS U.K.D. and P.D. thank CSIR, New Delhi, for their Senior Research Fellowship (SRF) and financial support, respectively. All the single-crystal X-ray diffraction data were collected at the Department of Biotechnology (DBT) funded Single Crystal Diffractometer facility at the Department of Organic Chemistry, IACS, Kolkata. 4569



Article

T.; Hanabusa, K.; Shirai, H. Adv. Mater. 2004, 16, 335. (t) de Jong, J. J. D.; Lucas, L. N.; Kellogg, R. M.; van Esch, J.; Feringa, B. L. Science 2004, 304, 278. (u) Oda, R.; Huc, I.; Candau, S. J. Angew. Chem., Int. Ed. 1998, 37, 2689. (v) Pal, A.; Sen, S.; Bhattacharya, S. Chem.Eur. J. 2008, 14, 6534. (w) Bhattacharya, S.; Ghosh, Y. K. Chem. Commun. 2001, 185. (7) Luboradzki, R.; Gronwald, O.; Ikeda, M.; Shinkai, S.; Reinhoudt, D. N. Tetrahedron 2000, 56, 9595. (8) (a) Trivedi, D. R.; Ballabh, A.; Dastidar, P.; Ganguly, B. Chem. Eur. J. 2004, 10, 5311. (b) Trivedi, D. R.; Ballabh, A.; Dastidar, P. Chem. Mater. 2003, 15, 3971. (c) Trivedi, D. R.; Dastidar, P. Cryst. Growth Des. 2006, 6, 1022. (d) Trivedi, D. R.; Dastidar, P. Cryst. Growth Des. 2006, 6, 2114. (e) Trivedi, D. R.; Ballabh, A.; Dastidar, P. J. Mater. Chem. 2005, 15, 2606. (f) Sahoo, P.; Sankolli, R.; Lee, H.-Y.; Raghavan, S. R.; Dastidar, P. Chem.Eur. J. 2012, 18, 8057. (9) (a) Ballabh, A.; Trivedi, D. R.; Dastidar, P. Cryst. Growth Des. 2005, 5, 1545. (b) Trivedi, D. R.; Ballabh, A.; Dastidar, P. Cryst. Growth Des. 2006, 6, 763. (c) Sahoo, P.; Kumar, D. K.; Trivedi, D. R.; Dastidar, P. Tetrahedron Lett. 2008, 49, 3052. (10) (a) Trivedi, D. R.; Dastidar, P. Chem. Mater. 2006, 18, 1470. (b) Ballabh, A.; Trivedi, D. R.; Dastidar, P. Chem. Mater. 2006, 18, 3795. (c) Das, U. K.; Trivedi, D. R.; Adarsh, N. N.; Dastidar, P. J. Org. Chem. 2009, 74, 7111. (d) Sahoo, P.; Kumar, D. K.; Raghavan, S. R.; Dastidar, P. Chem.Asian J. 2011, 6, 1038. (11) (a) Ballabh, A.; Trivedi, D. R.; Dastidar, P. Org. Lett. 2006, 8, 1271. (b) Sahoo, P.; Adarsh, N. N.; Chacko, G. E.; Raghavan, S. R.; Puranik, V. G.; Dastidar, P. Langmuir 2009, 25, 8742. (c) Sahoo, P.; Puranik, V. G.; Patra, A. K.; Sastry, P. U.; Dastidar, P. Soft Matter 2011, 7, 3634. (12) Das, U. K.; Puranik, V. G.; Dastidar, P. Cryst. Growth Des. 2012, 12, 5864. (13) Ballabh, A.; Trivedi, D. R.; Dastidar, P. Org. Lett. 2006, 8, 1271. (14) (a) Babu, A. M.; Weakley, T. J. R.; Murthy, M. R. N. Acta Crystallogr. 1997, C53, 365. (b) Moritani, Y.; Kashino, S. Acta Crystallogr. 1991, C47, 461. (c) Urbańczyk-Lipkowska, Z. Cryst. Eng. 2000, 3, 227.

4570


Extending Primary Ammonium Dicarboxylate (PAD) to Diprimary

Recommend Documents