Open Journal of Inorganic Chemistry
Vol.3 No.4(2013), Article ID:38091,9 pages DOI:10.4236/ojic.2013.34012

Structural studies and conductivity of [Fe(O3C4)(COO)]∙H2O based H4btec (H4btec = 1,2,4,5-benzenetetracarboxylic acid)

Manel Halouani1*, Mohamed Abdelhedi1, Mohamed Dammak1, Nathalie Audebrand2, Lilia Ktari1

1Laboratoire de Chimie Inorganique, Faculté des Sciences de Sfax, Université de Sfax, Sfax, Tunisia

2Laboratoire de Matériaux Inorganiques: Chimie Douce et Réactivité, UMR 6226 Sciences Chimiques de Rennes, Université Rennes 1, Rennes, France

Email: *,,,,

Copyright © 2013 Manel Halouani et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Received 17 June 2013; revised 17 July 2013; accepted 24 July 2013

Keywords: Hydrothermal Synthesis; X-Ray Diffraction; Crystal Structure


A new metal-organic hybrid compound [Fe(O3C4)(COO)]∙H2O I has been hydrothermally synthesized and characterized by single-crystal X-ray diffraction. Rust crystals crystallize in the monoclinic system, space group I2/a, a = 6.9651(2) Å, b = 8.12630(10) Å, c = 19.4245(2) Å, β = 92.6600(10)˚; V = 1098.25(4) Å3; Z = 2 and Dx = 3.63 g/cm3. The refinement converged into R = 0.042; Rw = 0.058. The structure, determined by single crystal X-ray diffraction, consists of a network of FeO6 centers, octahedral coordinated by btec (btec = 1,2,4,5-benzenetetracarboxylic acid) anions giving rise to a two-dimensional sheet structure. In the compound I, [Fe(O3C4)(COO)]∙H2O, the FeO6 group bridged by the 1,2,4,5-benzenetetracarboxyl anion exist in a unit cell, with each anion lying about an inversion centre. One of the FeO2 a distance [1.965(2)] significantly corresponds to the shortest distance as the other and the distances found in the axial direction of compound I.


During the past decade, the design and synthesis of crystalline material constructed from molecular clusters linked by extended groups have attracted great attention. Most notable fields are metal-organic frameworks (MOFs), [1-7] in which polyatomic inorganic metal-containing clusters are connected by polytopic linkers. The direct driving forces originate not only from their fascinating topological structures but also from their versatile applications in gas adsorption and separation, catalytic activities, optoelectronic material, luminescence, magnetism, and so on [8-19]. Thus, structural design or modification of the coordination polymers has become a very active field in crystal engineering [20-24]. In this process, judicious selection of ligands as basic building blocks is of great importance because slight structural changes in the organic building blocks such as length, flexibility, and symmetry can dramatically change the structural motifs of coordination polymers. It is well known that organic ligands play a rather important role in the construction of MOFs, and multicarboxylate ligands are frequently chosen owing to their rich coordination modes, coordinating to metal ions through complete or partial deprotonation of their carboxy groups, and their metal binding ability [25-30]. Especially interesting are the complexes formed by H2bdc and H3btc having one-dimensional polymeric chain or brick-wall structures and their selective guest binding abilities [31- 46].

In spite of the rich coordination chemistry exhibited by H2bdc and H3btc (Chart 1) in the presence of auxiliary ligands and coordinated solvents, barring a few sporadic reports, which mainly concentrate on the direct interaction between the metal ion and the ligand, there have been no serious attempts to prepare metal-organic polymeric or supramolecular structures based on 1,2,4,5- benzene tetracarboxylic acid (H4btec) [47-65]. It may be argued that, due to steric reasons, all the four carboxyl groups of H4btec are unlikely to take part in coordination to the metal. However, even the presence of free -COOH groups (especially in the vicinity of coordinated water molecules, donor solvents and added amines) would lead to formation of new extended structures aided by hydrogen bonding inter-actions. Moreover, the presence of a large number of uncoordinated water molecules within the lattice, may in turn lead to interesting possibilities for the preparation of porous solids. 1,2,4, 5-Benzenetetracarboxylic acid (H4btec) has been well known to be an ideal ligand to encapsulated metal nodes, forming coordination compounds with unique structures and interesting properties [66-70], which may have the following advantages: 1) Higher symmetry of the ligand may cause the generation of regular structures; 2) The rigidity of the ligand may reduce the possibility of lattice interpenetration in the products [71,72]; 3) The multidentate carboxylate is known to be essential in chelating metal ions to form chain-like units with M-O-M connectivity; 4) The four carboxylic groups of this ligand may chelate to metal ions by using various coordination modes to form fascinating multidimensional compounds. In consideration of the varieties of topologies and properties, incorporating functional moieties into MOFs is often a popular method used in crystal engineering.


2.1. Synthesis and Initial Characterization

The title compound was synthesized under hydrothermal conditions in the presence of tetramethylammonium nitrate. In a typical synthesis, 0.1158 g of pyromellitic acid (Acros Organics) was dispersed in 9 ml of H2O. To this, 0.1975 g of iron nitrate monohydrate (Prolabo) was added under constant stirring. Finally, we add 0.062 g of tetramethylammonium nitrate (Alfa Aesar) and the mixture was homogenized for 15 min at room temperature, was sealed in a 23-ml PTFE-lined stainless steel autoclave and heated at 120˚C for 60 h. Then the product obtained is filtered and washed with a small amount of distilled water. The chemical purity of the product was tested by EDAX measurements. [Figure 1(a)] presents


Figure 1. (a) Typical EDAX spectrum of [Fe(O3C4)(COO)]∙H2O showing the presence of Fe, O and C; (b) Scanning electron microscopic image of the [Fe(O3C4)(COO)]∙H2O.

the EDAX spectrum of [Fe(O3C4)(COO)]∙H2O which reveals the presence of all non-hydrogen atoms: Fe, C and O. Elemental analysis give these results: for observed we have C 34.10%, O 43.52%, Fe 2.38%; whereas for calculated we find C 43.93%, O 47.08%, Fe 8.99%. The amine used in this synthesis does not appear in the reaction product and its role remains unexplained. The [Figure 1(b)] shows the photograph of scanning electron microscopy (SEM) of the samples [Fe(O3C4)(COO)]∙H2O at room temperature.

2.2. Single Crystal Structure Determination

The unit-cell dimensions were refined using X-ray diffraction data collected with a Kappa CCD Enraf Noninus diffractometor using Mo Kα radiation .The structure, [Fe(O3C4)(COO)]∙H2O, was analyzed with the crystallographic CRYSTALS program [73]. The structure was solved by conventional Patterson and difference-Fourier techniques. The chemical crystal data, the parameters used for X-ray diffraction data collection and strategy used for the crystal structure determination and their results, are listed in Table 1. Table 2 shows the atomic coordinates and equivalent isotropic displacement. The anisotropic displacement parameters are listed in Table 3. Selected bond distances and angles are given in Table 4. Structural graphics were created by the DIAMOND program [74]. The asymmetric unit is shown in (Figure 2).


The structure of compound I is representatively described in detail here. In an asymmetrical unit of 2, The structure of [Fe(O3C4)(COO)]∙H2O , Compound I, is formed of a network of octahedral coordination by Fe carboxylate units btec. It also contains 11 non-hydrogen atoms. The Fe atom is octahedrally coordinated by six oxygen atoms from four different carboxylic groups. The Fe-O distances are in the range 1.965(11) - 2.038(4) (av.2.013 Å) and the O-Fe-O angles are in the range 86.34(16) - 179.994° (av.102.856°). Bond valence sum calculations 23 indicated that the valence states of the Fe, C and O in II were +2, +4 and −2 respectively. Their selected bond lengths and bond angles are listed in Table 4.

The bonded oxygen atoms of the carboxylate groups have C-O distances in the range 1.276(5) - 1.290(5)Å. The O-C-O bond angles have an average value of 125.16. The present compound adds another example to this family of compounds. The various structural parameters observed in the present compound are in agreement with those observed before. The present compoun d adds another example to this family of compounds. The various structural parameters observed in the present compound are in agreement with those ob-

Figure 2. Asymmetric unit of [Fe(O3C4)(COO)]∙H2O. Thermal ellipsoids are given at 50% probability.

Table 1. Crystallographic data for [Fe(O3C4)(COO)]∙H2O.

served before. The structure of [Fe(O3C4)(COO)]∙H2O, compound I, consists of a network of octahedral Fe centers coordinated by the btec carboxylate units (Figure 2). The connectivity between these units gives rise to a two dimensional hybrid layered structure in the ac and bc planes as shown in (Figures 3 and 4). The structure re-

Table 2. Fractional atomic coordinates and equivalent isotropic displacement for [Fe(O3C4)(COO)]∙H2O.

Table 3. Anisotropic displacement parameters (Å2).

Table 4. Main interatomic distances (Å) and bonds angles (deg).

sembles a 4-connected network in which each Fe atom is connected to four btec anions and each btec anion is linked to two Fe2+ ions. The water molecules also occupy the interlamellar region.


In this work, we report a novel metal–organic complex [Fe(O3C4)(COO)]∙H2O (I), which is prepared by the hydrothermal synthesis route. It crystallizes in the monoclinic symmetry, space group I2/a. Compound I exhibits a novel bi-dimensional network constructed from bridging btec ligand. The successful isolation of compound I not only confirms that such metal–organic compounds may be designed and synthesized according to the inherent stereo and interactive information stored in the organic ligands and metal ions [75], but also further proves the strong capability of hydrothermal reactions in preparing novel metal–organic materials with mixed or-

Figure 3. The projection structure of [Fe(O3C4)(COO)]∙H2O, in the ac plane showing a single layer.

Figure 4. The projection structure of [Fe(O3C4)(COO)]∙H2O, in the bc plane showing a single layer.

ganic ligands.


This work is supported by the minister of superior education and research.


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