Sels hybrides organiques-inorganiques obtenus par auto-assemblage de la brique anionique tris(oxalato)ferrate(III) et des cations pyridiniums: Synthèse, caractérisation et propriétés magnétiques

Abstract

Within the scope of this thesis, three new organic-inorganic hybrid salts of general formula (Org-H)3[MIII(C2O4)3]∙nH2O (Org-H = pyridinium derivative) in which the ionic couple (Org-H)+/[MIII(C2O4)3]3-is in the exact ratio of 3:1, were synthesized and fully characterized. They are :tris(2amino4,6dimethylpyridinium)tris(oxalato)ferrate(III), (C7H11N2)3[FeIII(C2O4)3](1), tris(4-dimethylaminopyridinium)tris(oxalato)ferrate(III) tétrahydrate,(C7H11N2)3[FeIII(C2O4)3]∙4H2O (2) and tris(2,6-diaminopyridinium) tris(oxalato)ferrate(III) trihydrate, (C5H8N3)3[FeIII(C2O4)3]∙3H2O (3). In the solid state, salt 1 is in the form of plate green crystals and it crystallizes in the triclinic P-1 space group. Salt 2 is in the form of plate greenish-yellow crystals and it crystallizes in monoclinic C2/c space group. Salt 3 crystallizes in triclinic P-1 space group like salt 1. Each compound contains the anionic complex [Fe(C2O4)3]3− in which the central metal is six-coordinate in a slightly distorted octahedron defined by three chelating oxalato(2-) ligands. The two substituted pyridinium cations are isomers. However, due to the great steric hindrance provided by the bulky cation, 2-amino-4,6 dimethylpyridinium, only the 4-dimethylaminopyridinium and (2,6-diaminopyridinium) cations, the smallest of this series, led to formation of salts 2 and 3, respectively, with enough vacant spaces to be occupied by solvent water molecules. In addition to the stabilizing effect of the π-π interactions between the pyridine rings, extended H-bonding of the types N–H···O in 1 and N–H···O and O–H···O in 2 and 3, contribute to consolidate the crystal packing.The results of elemental analysis are in agreement with the crystalline structure of the synthesized salts. Infrared absorption spectra confirm the presence of the oxalato(2-) ligands and the organic cations in the salts. The thermal studies confirmed the anhydrous character of salt 1 and the presence of water molecules of crystallization in salts 2 and 3. The magnetic susceptibility measurements in the 2-300 K temperature range revealed weak antiferromagnetic couplings in the three salts.