Sels hybrides Oxalatom étalate(III) mono- et polymétalliques (MIII = Cr, Fe) avec les cations Pyridiniums : synthèse, caractérisation et propriétés magnétiques.

Abstract

Within the framework of this thesis, four new organic-inorganic hybrid salts were synthesized, characterized spectroscopically and structurally. These are: a) (C7H11N2)3[Cr(C2O4)3] (C7H11N2+ = 2-amino-4,6-dimethylpyridinium) (1), b) (C5H8N3)2(NH4)[Cr(C2O4)3]·2H2O (C5H8N3 + = 2,6-diaminopyridinium) (2), c) (C5H7N2)6[Ba3(H2O)5,1Cr4(C2O4)12]∙5H2O (3) et d) (C5H7N2)6[Ba3(H2O)5,3Fe4(C2O4)12]∙5H2O(4) (C5H7N2 + = 3-aminopyridinium). The magnetic properties have been investigated. Compounds 1 and 2, with monometallic complex anion ([Cr(C2O4)3]3-), were obtained by ion exchange reaction between tris(ammonium) tris(oxalato)chromate(III) trihydrate ((NH4)3[Cr(C2O4)3]·3H2O) and pyridinium salt (Org-H)2C2O4 in aqueous medium (3 ≤ pH ≤ 4) to avoid destruction of the anionic tris(oxalato)chromate(III) brick. Compounds 1 and 2 crystallize in the triclinic P-1 and monoclinic C2/c space group, respectively. The chiral, trischelated [Cr(C2O4)3]3- anion is present in both compounds with distorted octahedral geometry around chromium(III) cations. Compounds 1 and 2 are thermally stable and melt at 288 °C and 210 °C, respectively. Compounds 3 and 4 are iso-structural, with polymetallic heptanuclear complex anion ([Ba3(H2O)mM4(C2O4)12]6- (M= Cr3+ or Fe3+ and m= 5,1 or 5,3). They are obtained by metathetic reaction between pyridinium salt (Org-H)2C2O4 in aqueous medium (3 ≤ pH ≤ 4) with barium tris(oxalato)chromate(III) {Ba6[Cr(C2O4)3]4}∙24H2O and barium tris(oxalato)ferrate(III) {Ba6[Fe(C2O4)3]4}∙24H2O, respectively. They crystallize in the monoclinic C2/c. They are thermally stable until 300 °C. The crystal packing is consolidated by H-bonding of the types N–H···O in 1 and N–H···O and O–H···O in 2, 3 and 4. In addition the stabilizing effect of the π-π stacking interactions between the pyridine rings in 1, 3 and 4, contribute to stabilize the framework. The presence of two types of cations in compound 2 excludes the formation of π - π interactions. The thermal studies confirmed the anhydrous character of salt 1 and the presence of water molecules of crystallization in salts 2, 3 and 4. The results of elemental analysis are in agreement with the crystalline structure of the synthesized salts. The magnetic susceptibility measurements in the 2-300 K temperature range revealed weak antiferromagnetic couplings in the four salts.