Préparation, caractérisation structurale et physico-chimique de nouveaux composés de coordination des métaux zinc et cuivre
- Autores: Zeineb Basdouri
- Directores de la Tesis: Mohsen Graia (dir. tes.), Lawrence Falvello (dir. tes.)
- Lectura: En la Universidad de Zaragoza ( España ) en 2020
- Idioma: español
- Tribunal Calificador de la Tesis: Rosa María Llusar Barelles (presid.), Irene Victoria Ara Laplana (secret.), Sònia Abad Florensa (voc.)
- Materias:
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- Resumen
We summarize here the most important aspects of the work carried out in this Thesis and described in the previous chapters, together with its conclusions. The thesis, entitled "Preparation, structural and physicochemical characterization of novel coordination compounds of zinc and copper" is based on the study of coordination compounds, formed on the one hand by zinc with the hexamethylenetetramine ligand and on the other hand by copper with the orotate ligand. This work has been divided into six chapters for a clearer exposition of the results obtained.
In the first chapter, we present general information on coordination chemistry in order to reprise some basic concepts, followed by a brief review of the intermolecular interactions that provide the stability and cohesion among the entities in the solids reported in this thesis. A bibliographic study is also presented, based on the complexes formed by the metals and ligands used in this work for the development of new coordination compounds. This begins with a brief introduction to coordination chemistry followed by a definition of a coordination complex and the entities that form it. We also focus on the geometries that can be found in coordination complexes as well as the steps to follow in order to name such a complex. The text continues with an overview of the phenomena of crystallization and polymorphism followed by a description of Ostwald’s rule of stages. In the remainder of this chapter, intermolecular interactions such as hydrogen bonds, Van der Waals forces and - interactions, which are responsible for the cohesion and stability of our synthesized materials, are discussed. Regarding the bibliographic study, we present in the rest of this chapter the principal characteristics of zinc and copper as well as the ligands hexamethylenetetramine and orotic acid, accompanied by some examples of the complexes synthesized previously, as drawn from the literature with their crystallographic characteristics.
In the second chapter, the different characterization techniques used in this work as well as the associated experimental devices are described. After a brief introduction, the principles and practical implementation of X-ray structure analysis are presented. This technique is the mainstay of our work. After a suitable crystal has been chosen and mounted for single crystal X-ray diffraction, the analysis is carried out in three steps. The first step is to determine the crystal lattice, then perform the data collection and finally solve the structure. For our compounds, we have used two types of diffractometers; one is an Enraf-Nonius CAD-4 with FR590 X-ray generator, and the other is a Rigaku/Oxford Diffraction Xcalibur/Sapphire 3. The thesis describes in detail the different steps for the two diffractometers. Subsequently, the text describes the principle of Hirshfeld surface analysis, which allowed us to study the intermolecular interactions in our synthesized compounds. The principle of X-ray powder diffraction is described; this analysis allowed us to ensure the purity of our compounds using the Rietveld method, which is described later. In the rest of this chapter, we also describe the principle and the equipment of infrared absorption spectroscopy, used to study the vibrations of the different functional groups in our synthesized materials. This chapter ends with background on thermal analysis and especially thermogravimetric analysis (TGA) to study the stability and thermal behavior of our materials.
The third chapter is focused on the study of organic-inorganic hybrid compounds based on zinc and hexamethylenetetramine. A brief introduction is followed by a description of the synthetic procedure and the strategy for preparing crystals. This chapter presents a study of three hybrid zinc compounds. These are prepared by slow evaporation of solvent at room temperature; two of the new products emerge from the same preparation. The detailed structural study as well as the Hirshfeld surface analysis of two anhydrous complexes, [hmtaH]ZnCl3 and (hmtaCH2OH)ZnCl3, are presented. The first compound, of formula (C6H13N4)ZnCl3, crystallizes in the orthorhombic system, space group Pnma. Its structure is formed by [hmtaH]ZnCl3 molecules. These entities arrange in layers parallel to the (101) plane. The cohesion between the molecules is ensured by N-H...Cl and C-H...Cl hydrogen bonds within layers and by van der Waals interactions between layers. The second compound, of formula (C7H15N4O)ZnCl3, crystallizes in the triclinic system, space group P-1. Its structure is formed of discrete [(C7H15N4O)ZnCl3] molecules, which in the crystal form a compact bimolecular aggregate. O-H...Cl hydrogen bonds connect neighbouring molecules, forming an unbounded chain of dimers. The cohesion of the structure is maintained by Van der Waals interactions between neighbouring chains of dimers. The Hirshfeld surface analysis confirms the type of intermolecular interactions responsible for the structural stability of these compounds. The remainder of this chapter deals with the structural, comparative and physicochemical study of the hemihydrate compound [Zn(H2O)6][{(CH2)6N4}ZnCl3]2·0.5H2O. The structural study establishes that it crystallizes in the trigonal system, space group P-3c1. Its structure can be described as consisting of stacks parallel to the crystallographic c axis: Firstly, cationic Zn1(O1WH2)6 octahedra and disordered unligated water molecules line up along the three-fold symmetry axis at x = 0, y = 0; secondly, the anionic complexes are arranged along the threefold axes at (1/3, 2/3, z) and (2/3, 1/3, z). The stability of this arrangement is governed by O-H…N and O-H…Cl hydrogen bonding interactions between cation and anion chains, with a lesser contribution within the cation/water chains from O-H…O H-bonds with the partially occupied free water as receptor. It is noted that this material is the second hydrate synthesized in this system. The relationship between the packing in the new structure and that of the previous hexahydrate [Zn(H2O)6][{(CH2)6N4}ZnCl3]2·6H2O, which was reported by Thomas C. W. Mak in 1986, is described. The comparative study showed that the two structures differ essentially in the proportion and arrangement of the water of hydration. The purity of this compound was checked by X-ray powder diffraction analysis using the Rietveld method. Then, for the vibrational study of our material, a theoretical semi-empirical calculation of the infrared spectrum using the Cache program was carried out in order to compare the different bands in the theoretical spectrum with those in the experimental spectrum. The thermal stability of this hemihydrate compound was subsequently studied by TGA-DTG. Finally, Hirshfeld surface analysis and fingerprint plots were applied to confirm the existence of weaker intermolecular interactions in the crystal.
In the fourth chapter, we present the study of two copper orotates of formulas (Cs)2[Cu(orotate)2(H2O)2]·4H2O and (Cs)2[Cu(orotate)2]·2H2O, which were synthesized from the same starting solution. The first compound is not stable and it changes over time to give rise to crystals of the second phase. These two compounds crystallize in the triclinic system, space group P-1. The structure of the (Cs)2[Cu(orotate)2(H2O)2]·4H2O compound is formed by layers of [Cu(HOr)2(H2O)2]2- anions parallel to the (001) plane. The layers are linked to each other by hydrogen bonds involving the H2O2W and H2O3W water molecules. The cesium cations are located in the inter-layer space and also contribute to the cohesion between layers. As for the structure of (Cs)2[Cu(orotate)2]·2H2O, it presents a layer of double chains of bimolecular complex aggregates parallel to (010). N3-H3 ... O14 and N13-H13 ... O4 hydrogen bonds ensure cohesion and progression in a chain. The hydration water molecules as well as the Cs+ cations are located in the inter-layer space and ensure cohesion between layers. Subsequently, the comparative study of Cs2[Cu(orotate)2(H2O)2]·4H2O with its isomorph of the previously studied analogous nickel compound, namely Cs2[Ni(HOr)2(H2O)2]·4H2O, has been conducted.
In fact, the two structures have a clear resemblance and some points of difference. However, this is due to the Jahn-Teller effect, which is present only in the copper compound. The transformation of crystals of the first compound into crystals of the second compound involves the egress of four water molecules per formula unit accompanied by the modification of the coordination about the copper center from octahedral six-coordinate to distorted square pyramidal [4+1]. Both compounds have also been characterized by infrared absorption spectroscopy followed by thermal analysis, TGA-DTG, for the (Cs)2[Cu(orotate)2]·2H2O compound.
In the fifth chapter, we describe the study of a new copper orotate with the organic cation guanidinium, of formula, (CH6N3)2[Cu (orotate)2]·2H2O. This complex has been synthesized by slow evaporation of solvent at room temperature. Its structure is formed by layers of the [Cu(HOr)2]2- anion and hydration water molecules parallel to the (001) plane. Between these layers, the guanidinium cations (CH6N3)+ are located; they are all linked together via hydrogen bonding interactions. Analysis of the Hirshfeld surfaces aids in the interpretation of the intermolecular interactions. Thermal analysis has shown that this compound is stable at temperatures ≤ 100°C. The comparative study with Cs2[Cu(HOr)2]·2H2O shows the effect of the change of counterion on the structure and non-covalent interactions. It is noted that the compound (CH6N3)2[Cu(HOr)2]·2H2O is more stable than the analogue with the Cs+ cation; this can be explained by the capacity of the guanidinium cation (CH6N3)+ to form hydrogen bonds, which enhances its contribution to maintaining the stability of the compound.
In the sixth and last chapter, we have identified a crystallization process showing a neat solution-mediated single crystal to single crystal transformation between two conformational polymorphs of (nBu4N)2[Cu(orotate)2]·2H2O, with the co-existence of both forms in the same experimental conditions for an extended period of time; on this basis they might be considered concomitant polymorphs. However, the crystal transformation process obeys Ostwald’s rules of stages with superposition of the corresponding domains. The two polymorphs can be distinguished by their difference in colour and their morphologies. The crystals of form I develop as blue green needles while those of form II are blue-purple blocks. The square planar geometry around the Cu2+ ion for polymorph I is distorted while in polymorph II it is flat. The geometry calculated by the program SHAPE has a deviation of 5.08% compared to an ideal square-planar coordination and 16.01% compared to an ideal tetrahedral coordination for form I and a 0.41% deviation from an ideal square-planar coordination and 33.61% compared to an ideal tetrahedral coordination for form II. Polymorph I of (nBu4N)2[Cu(orotate)2]·2H2O crystallizes in the monoclinic system, space group P21/n; as for polymorph II, it crystallizes in the same crystal system, with space group P21/c. The structures of these two polymorphs are constituted by anionic ribbons formed by [Cu(HOr)2]2- anions and uncoordinated water molecules extending along the a axis. The cohesion within a ribbon is ensured by hydrogen bonds. The inter-ribbon space is filled by nBu4N+ cations. The cohesion between the anionic ribbons and the organic cations is maintained by van der Waals interactions. The contributions of the interactions observed on the Hirshfeld surface (dnorm) and the corresponding 2D fingerprints plots for the two polymorphs are very similar. X-ray powder diffraction analysis allowed us to confirm the purity of the two compounds using the le Bail method. Detailed vibrational study by infrared absorption spectroscopy and thermal analysis by TGA-DTG were conducted. IR spectroscopy analysis showed the decrease of symmetry in form I compared to form II. This results in a splitting of the vibration bands. According with the TGA data, both crystals lose their water molecules below 90°C with the water molecules of form I being lost at a slightly lower temperature (DTGmax = 72.35°C), which could indicate that the hydrogenbonding system is a bit stronger in the final planar compound (form II, DTGmax = 80.14°C).
Additionally, the final compound has a slightly larger volume (>2.5%, 1262.8 Å3/mol) than the first one (1228.3 Å3/mol), which could be related to the entropy of the systems. After the loss of water, the TGA curves are not identical, which indicates that they do not evolve towards the same compound upon heating. DFT calculations on the complex anion realized by Dr. Miguel Baya García reveal a slight energetic advantage for the distorted conformation, from which the conclusion is drawn that crystals of form II, which according to Ostwald's Rule of Stages are more stable than those of form I, are energetically favored as a result of the hydrogen bonding.
