Synthèse, caractérisation et propriétés magnétiques de nouveaux sels hybrides bis(oxalato)chromate(III) et cuprate(II)

Abstract

Within the scope of the present thesis, three new organic-inorganic hybrid salts have been synthesized and fully characterized. They include: guanidinium transdiaquabis(oxalato)chromate(III) dihydrate, (CH6N3)[Cr(C2O4)2(H2O)2]·2H2O (1), bis(4- diméthylaminopyrydinium) bis(oxalato)cuprate(II) oxalic acid monosolvate, (C7H11N2)2[Cu(C2O4)2]·H2C2O4 (2), bis(3-aminopyridinium) trans- iaquabis(oxalato)- cuprate(II) oxalic acid disolvate, (C5H7N2)2[Cu(C2O4)2(H2O)2]·2H2C2O4 (3). Salt 1 is blood red crystals and it crystallizes in the monoclinic C2/c space group. The structural feature of focal interest in 1 is the formation of pillars of [Cr(ox)2(H2O)2]‒ complex anions and CH6N3+ guanidinium cations. The 3D supramolecular architecture is stabilized through a network of intermolecular hydrogen bonding interactions: N–H∙∙∙O and O–H∙∙∙O. Salt 2 and 3 are sky blue crystals and crystallize in triclinic P-1 space group. The two structures differ in terms of the coordination ligands around the Cu(II) centers as well as the number of the lattice oxalic acid molecules. The crystal structure of 2 is made of columnar stacks of [Cu(C2O4)2]2– anions through axial Cu∙∙∙O contacts (2.89 Å), yielding straight Cu(II) chains. The crystal structure of 3 is characterized by the trans -diaquabis(oxalato)cuprate(II), [Cu(C2O4)2(H2O)2]2– complex anion. This trans configuration is unusual in bis(oxalato)cuprate(II) compounds. In compounds 2 and 3, the cohesion of the crystal packing is ensured by hydrogen bonding interactions (N–H∙∙∙O and O–H∙∙∙O) and π–π stacking interactions between pyridine rings. 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 presence of water molecules in salts 1 and 3 and the anhydrous character of salt 2. The decrease of XMT with decreasing temperature revealed weak antiferromagnetic couplings in the three salts.