Supramolecular Loop-Chain Network of Pillared Layers via 4,4′-Bipyridine Ruiz-Pe´rez,*,§
Lorenzo-Luis,#
Catalina Pablo A. Marı´a M. Milagros Laz,‡ Pedro Gili,# and Miguel Julve†
Herna´ndez-Molina,§
CRYSTAL GROWTH & DESIGN 2004 VOL. 4, NO. 1 57-61
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, Departamento de Quı´mica Inorga´ nica (Facultad de Farmacia), and 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 July 16, 2003;
Revised Manuscript Received September 8, 2003
ABSTRACT: A new structural motif occurs in the organic salt of formula {[H3bta]2[H2-4,4′-bpy]} 1 where stacks of infinite pillared rhombically distorted square grid networks are interpenetrated by the same pillared networks in a loop-chain modus. Interestingly, the X-ray structure of 1 reveals two [H3bta]- monoanions of piromellitic acid (benzene-1,2,4,5-tetracarboxylic acid, H4bta) and one [H2-4,4′-bpy]2+ cation in the asymmetric unit. Each H3btaunit builds up two different hydrogen-bonded sheets (A and B) which are parallel to the ab-plane. The [H2-4,4′bpy]2+ cation acts as a pillar along the c-axis linking nonadjacent A and B sheets to afford an extended threedimensional network. Introduction The intrinsic aim of crystal engineering (which explicitly addresses some of the challenges of materials design) is to control the assembly and orientation of solid-state structures in three dimensions.1 This task is severely complicated by the fact that ionic/molecular building blocks can adopt a vast number of conformations in the crystal, thus making predictions of the resulting structure extremely difficult. However, the unique characteristics of the hydrogen bond (selectivity and directionality) have allowed the preparation of a variety of distinctive and predictable structural aggregates,2 notably in molecular solids, the use of hydrogen bonding as a structural steering force emerging now as the most important strategy in crystal engineering. One of the goals in crystal engineering is the synthesis of sheetlike materials that mimic the lamellar structures of naturally occurring clays.3,4 This can be achieved by creating molecular two-dimensional (2D) scaffolds using hydrogen-bonded components (usually organic ions), with these sheets further separated by organic substituents.5,6 Clearly, these materials differ from naturally occurring clays and inorganic clay-like materials,7 as hydrogen bonds between organic ions replace the coordinate or coordinate-covalent (typically metal-oxide) bonds which are found in clays. In fact, a large number of hydrogen-bonded lamellar materials has been found and they act as hosts for a variety of molecular guest species via crystallization from solution.1,2 * To whom correspondence should be addressed. E-mail:
[email protected] (C. Ruiz-Pe´rez). § Laboratorio de Rayos X y Materiales Moleculares, Departamento de Fı´sica Fundamental II, Universidad de La Laguna. # Departamento de Quı´mica Inorga ´ nicia (Facultad de Farmacia), Universidad de La Laguna. ‡ Laboratorio de Rayos X y Materiales Moleculares, Departamento de Edafologı´a y Geologı´a, Universidad de La Laguna. † Facultad de Quı´mica de la Universitat de Vale ` ncia.
The research described in this contribution focuses on the supramolecular synthesis of solid materials that have flexible pillars suitable for the eventual intercalation of small molecules or ions. The pyromellitic acid (benzene-1,2,4,5-tetracarboxylic acid, noted as H4bta)4 was chosen as 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.8 This carboxylic acid can form homoor heterodimers with a variety of complementary functional groups such as pyridine, 2-aminopyridine, and pyrimidine, for instance. In addition, its deprotonated forms9 and metal complexes10 can be used as templates in crystal engineering studies. Recently, several papers focused on the use of 4,4′-bipyridine (hereafter noted 4,4′-bpy) as a design component in crystal engineering.11 O-H‚‚‚N type hydrogen bonds are formed when this molecule cocrystallizes with organic molecules containing carboxylic groups. In this paper, we report the preparation and structural characterization of an organic salt of pyromellitic acid, of formula [H3bta]2[H2-4,4′-bpy] 1, in which unprecedented and very complex hydrogen-bonding network involving charged organic molecules occurs. Experimental Section The reagents and solvents used in the synthesis were from commercial sources, and they were used as received. Elemental analyses (C, H, N) were performed with an EA 1108 CHNS-0 automatic analyzer. FT-IR spectra were recorded on a ThermoNicolet spectrometer (model Avatar 360 FT-IR), and the sample was prepared as a KBr pellet. Thermal analyses were carried out on a Perkin-Elmer system (model Pyris Diamond TG-DTA) under a dinitrogen atmosphere (flow rate: 80 cm3 min-1) in the temperature range 25-550 °C. The sample (3.624 mg) was heated in an aluminum crucible (45 µL) at a rate of 10 °C min-1. The TG curve was analyzed as mass loss as a
10.1021/cg034133i CCC: $27.50 © 2004 American Chemical Society Published on Web 10/25/2003
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Figure 1. Schematic representation of the loop-chain network of pillared layers (top) and crystal structure of 1 along the a-axis (bottom). The H2-4,4’-bpy serves as a pillar along the c-axis. Table 1. Crystal Data and Structure Refinement Details for 1 formula formula weight crystal system space group a/Å b/Å c/Å β/° volume/Å3 Z temp/K Dc/g cm-3 µ(Mo-KR)/mm-1 crystal type θ range (°) Rint reflections collected reflections observed [I > 2σ(I)] final R indices [I > 2σ(I)] final R indices (all data) largest diff. peak and hole (e Å-3)
C30H20O16N2 664.49 monoclinic Cc 12.012(2) 15.464(3) 15.418(3) 110.78(3) 2677.8(9) 4 293(2) 1.648 0.137 colorless blocks 2.83-29.96 0.0324 9755 5574 R1 ) 0.0530 wR2 ) 0.1207 R1 ) 0.0748 wR2 ) 0.1322 0.493 and -0.424
function of temperature. The number of decomposition steps was identified using the derivative thermogravimetric curve (DTG). The DTA curve was analyzed as differential thermal analysis [∆T(µV)]. Synthesis [H3bta]2[H2-4,4′-bpy] 1. H4bta (100 mg, 0.39 mmol), Cu(NO3)2‚3H2O (84 mg, 0.35 mmol), 4,4′-bpy (50 mg, 0.75 mmol), and NaOH (30 mg, 0.75 mmol) were mixed thoroughly in distilled water (6 mL) with vigorous magnetic stirring at ambient temperature for 1 h. The mixture was then transferred to a reaction vessel placed inside a preheated oven at 145 °C. The reaction proceeded for 3 h before the vessel
Table 2. Hydrogen Bonds in the Crystal Structure of 1a D-H‚‚‚A/Å
D‚‚‚A/Å
H‚‚‚A/Å
