Hydrogen Bond-Directed Frameworks Based on 1,2,4,5-Benzene-Tetracarboxylate Oscar Fabelo,§ Laura Can˜adillas-Delgado,§ Fernando S. Delgado,§ Pablo Lorenzo-Luis,# M. Milagros Laz,‡ Miguel Julve,† and Catalina Ruiz-Pe´rez*,§
CRYSTAL GROWTH & DESIGN 2005 VOL. 5, NO. 3 1163-1167
Laboratorio de Rayos X y Materiales Moleculares, Departamento de Fı´sica Fundamental II, Avda, Astrofı´sico Francisco Sa´ nchez s/n. Facultad de Fı´sica, Universidad de La Laguna, E-38204, Tenerife, Spain, Laboratorio de Rayos X y Materiales Moleculares, Departamento de Quı´mica Inorga´ nica (Facultad de Farmacia), Universidad de La Laguna, E-38204, Tenerife, Spain, Laboratorio de Rayos X y Materiales Moleculares, Departamento de Edafologı´a y Geologı´a, Universidad de La Laguna, E-38204, Tenerife, Spain, and Departamento de Quı´mica Inorga´ nica/Instituto de Ciencia Molecular, Facultad de Quı´mica de la Universitat de Vale` ncia, Dr. Moliner 50, 46100-Burjassot (Vale` ncia), Spain Received November 2, 2004;
Revised Manuscript Received December 21, 2004
ABSTRACT: The deprotonated forms of 1,2,4,5-benzenetetracarboxylic acid H4bta can act not only as hydrogenbond acceptors but also as hydrogen-bond donors, depending on the deprotonated carboxyl groups given different supramolecular adducts. A search of the Cambridge Structural Database (CSD) of cocrystal structures of H4bta with L ) 4,4′-bpy or bpe has found three different adducts: [HL]2[H2bta], [H2L][H2bta], and [H2L][H3bta], where cocrystal structures of [HL]2[H2bta] with L ) 4,4′-bpy or bpe form similar supramolecular arrangements. To investigate this similarity, two new organic salts of the formula {[H2-4,4′-bpy][H2bta]}‚2H2O (1) and {[H2bpe] [H3bta]2}‚4H2O (2) have been characterized. In the 1:1 adduct 1, the molecular components are linked by hydrogen bonds of the N-H‚‚‚O type creating chains. These chains are further linked by C-H‚‚‚O type interactions (C-H from the cation and O from the anion) creating a two-dimensional motif. Two types of centrosymmetric rings are evident in the sheets. The stacked sheets are held together via π‚‚‚π interactions to create a three-dimensional network. Two types of channels, one hydrophilic and the other hydrophobic, run parallel to the a-axis. Water molecules are hydrogen bonded in the hydrophilic channels. The supramolecular structure in the 2:1 adduct 2 is due to hydrogen bonds of the O-H‚‚‚O and N-H‚‚‚O types that afford a railroad network along the a-axis. Two water molecules are held in the railroad cavities by hydrogen bonds with carboxylate oxygen atoms. Adjacent railroad chains are linked through hydrogen bonds involving water molecules, building a two-dimensional structure. Introduction The ultimate goal of crystal engineering is to design specific crystal structures with potential specific physical and chemical properties, based only on the knowledge of the building blocks.1,2 An important approach to control crystal structure is the consideration of robust and reliable intermolecular interactions, such as strong hydrogen bonds. In principle, by placing functional groups properly, supramolecular motifs, for example, tapes, two- and three-dimensional (nD) networks, can be formed via hydrogen bonds.1,2 From a supramolecular perspective, binary components represent an illustration of how one might exploit the modular approach to design new supermolecules, especially in the solid state. It is reasonable to assert that supramolecular synthesis of new classes of cocrystals and modular solids offers the potential to increase the known range of crystalline materials by 2 or 3 orders of magnitude and to facilitate combinatorial approaches to material science. For example, if one were to consider only cocrystals that are sustained by hydrogen bonding, a wide range of com* To whom correspondence should be addressed. E-mail:
[email protected]. § Departamento de Fı´sica Fundamental II, Universidad de La Laguna. # Departamento de Quı´mica Inorga ´ nica, Universidad de La Laguna. ‡ Departamento de Edafologı´a y Geologı´a, Universidad de La Laguna. † Departamento de Quı´mica Inorga ´ nico/Instituto de Ciencia Molecular, Universitat de Vale`ncia.
positions exists that remains to be explored. Perhaps it is a sobering thought to realize that, at least in principle, with molecules that contain excess hydrogen-bond acceptors. Even if one considers only simple examples such as pyridines, there are many permutations for the formation of binary compounds. Such a strategy could be important in the context of supramolecular derivatives of drugs and functional materials (i.e., modification of bulk properties without changing the molecular structure of the active species), or they could serve as precursors to covalent products, including polymers. Such an approach has already been effective in formulation of Polaroid films.3 In this context, high-symmetry molecules are of particular interest in the design of supramolecular architectures; pyromellitic acid (benzene-1,2,4,5-tetracarboxylic acid, noted as H4bta)4 was chosen as a building unit for the layers because it is a molecule with predictable and interesting supramolecular properties (catenation or interpenetration, polymorphism and inclusion) as a consequence of its molecular symmetry and complementary hydrogen-bonding capabilities.5 This carboxylic acid can form homo- or heterodimers with a variety of complementary functional groups such as pyridine, 2-aminopyridine, and pyrimidine, for instance. In addition, its deprotonated forms6 and metal complexes7 can be used as templates in crystal engineering studies. Recently, several papers focused on the use of
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Figure 1. Supramolecular arrangements of H4bta with L ) 4,4′-bpy or bpe from CSD: (a) [HL]2[H2bta], (b) [H2L][H2bta], and (c) [H2L][H3bta] adducts.
4,4′-bipyridine and 1,2-bis(4-pyridyl)ethylene (hereafter noted as 4,4′-bpy and bpe, respectively) as design components in crystal engineering.8 4,4′-bpy and bpe are able to generate supramolecular organizations with various organic molecules. Most frequently, 4,4′-bpy and bpe act as hydrogen-bond acceptors, although they can also be hydrogen-bond donors. The self-assembly process between 4,4′-bpy and bpe and organic molecules with exodentate functionality (trimesic acid,9 melamine,10 trithiocyanuric,7a and cyanuric acids11) leads to robust hydrogen-bonded supramolecular aggregates constructed with different synthons. For example, the cocrystallization of cyanuric acid with 4,4′-bpy in water affords a 1:1 adduct (a 2:1 adduct is formed in methanol). Hydrogen bonds of the type N-H‚‚‚O are formed when this molecule cocrystallizes with organic molecules containing carboxylic groups. A search of the Cambridge Structural Database (CSD)23 of cocrystal structures of H4bta with L ) 4,4′-bpy12 or bpe13 has found three different adducts: [HL]2[H2bta],12a-c,13a [H2L][H2bta],13b and [H2L] [H3bta]12d (Figure 1). Cocrystal structures of [HL]2 [H2bta] with L ) 4,4′-bpy12a-c or bpe13a forms similar supramolecular arrangements where the molecular components are linked by hard hydrogen bonds of O-H‚‚‚N and N-H‚‚‚O types into a chain of rings. At this point, we conjectured that cocrystals of 4,4′-bpy with H4bta would have similar supramolecular arrangements to the corresponding bpe cocrystals. The research described in this contribution focuses
Table 1. Crystal Data and Details of Structure Determination compound formula M crystal system space group a, Å b, Å c, Å R, deg β, deg γ, deg V, Å3 Z T (K) Fcalc (Mg m-3) λ (Mo KR Å) µ (Mo KR, mm-1) R1, I > 2σ(I) (all) wR2, I > 2σ(I) (all) measured reflections independent reflections
1 C20H18N2O10 446.37 triclinic P1 h 3.7978(8) 10.8331(19) 11.9389(17) 99.649(18) 97.359(14) 95.955(14) 476.30(15) 1 293(2) 1.598 0.71073 0.133 0.0702 (0.1222) 0.1522 (0.1815) 7284 4747
2 C32H30N2O20 762.59 triclinic P1 h 9.5544(5) 10.0595(5) 10.3309(6) 111.038(4) 93.268(5) 115.188(4) 812.34(8) 2 293(2) 1.559 0.71073 0.132 0.0471 (0.0865) 0.0964 (0.1089) 3672 2440
on the preparation and structural characterization of two new organic ionic salts of the formula {[H2bta] [H2-4,4′-bpy]}‚2H2O (1) and {[H2bpe][H3bta]2}‚4H2O (2)that allow the study of hydrogen-bonding networks involving charged organic molecules. Experimental Section All reagents and solvents used in the synthesis were purchased from commercial sources and used without further purification. Elemental analysis (C, H, N) were performed with an EA 1108 CHNS/0 automatic analyzer.
1,2,4,5-Benzene-Tetracarboxylate Frameworks
Crystal Growth & Design, Vol. 5, No. 3, 2005 1165 Table 3. Intermolecular Contacts in the Hydrophilic Channel of 1a
Figure 2. View of the chain resulting from the combination of pyromellitic acid and 4,4′-bpy in the 1:1 hydrogen-bonded organic salt in 1. Table 2. Geometries of the Hydrogen Bonds of 1a D-H‚‚‚A
d(D‚‚‚A) (Å)
D(H‚‚‚A) (Å)
