Sels hybrides organiques-inorganiques à base du tecton anionique iaquabis(oxalato)chromate(III) : Synthèse, caractérisation, propriétés magnétiques et électroniques et activités antibactériennes

Abstract

Within the scope of this work, two new organic-inorganic hybrid salts involving anionic diaquabis(oxalato)chromate(III) of general formula (OrgH)[Cr(C2O4)2(H2O)2]∙nH2O (OrgH+ = aliphatic amine organic monocation; n ≥ 0) were synthesized and characterized: a) pipéridinium trans- diaquabis(oxalato)chromate(III) tétrahydrate, (C5H10NH2)[Cr(C2O4)2(H2O)2]•4H2O (1); b) triéthylammonium trans- iaquabis(oxalato)chromate(III),[(C2H5)3NH][Cr(C2O4)2(H2O)2] (2). In the solid state, compounds 1 and 2 are in the form of prismatic purplish-red crystals. 1 crystallizes in the orthorhombic system, non-centrosymmetric space group Cmc21 with the unit cell parameters a = 7.4329 Å ; b = 9.9356 Å ; c = 23.6756 Å ; α = β = γ = 90 ° ; Z = 4 and V = 1748.45 Å3. Its molecular structure is formed by Cr(C2O4)2(H2O)2]- monometallic anion, piperidinium cation, C5H11NH+ in chair conformation and four water molecules of crystallization. 2 crystallizes in the orthorhombic system, Pbcn space group with the unit cell parameters a = 11.1776 Å ; b = 7.6105 Å ; c = 17.5654 Å ; α = β = γ = 90 ° ; Z = 4 and V = 1494.24 Å3. Its asymmetric unit consists of the [Cr(C2O4)2(H2O)2]- anionic complex and the triethylammonium ion, Et3NH+. The triethylammonium are disordered among two possible orientations with occupancies rates around 50 %. In 1 and 2, the central metal CrIII of the complex anion is coordinated in a slightly distorted octahedral environment, bischelating by two oxalato ligands in the equatorial plane, and two aqua ligands occupying the apical positions. X-ray analysis of the two structures is in agreement with the results of elemental analysis and reveals that the 3D packing of the lattice architectures is reinforced by extended O – H••• O and N – H•••O bridgings. The IR spectra of the two compounds are consistent with the presence of the various chemical bricks involved. The respective UV-Vis spectra of 1 and 2 show two absorption bands around 564 and 416 nm which are compatible with an anionic chromium(III) complex in an octahedral environment and the observed color of the materials. Thermal analysis reveals that 1 and 2 are stable up to 90 °C and 210 °C respectively and their decomposition leads to the formation of a chromium(III) oxide residue. Furthermore, this study confirms the presence of the water molecules of crystallization in 1 and the anhydrous character of 2. The number of solvent water molecules per formula unit in 1 seems to be the highest obtained so far for this family of bis(oxalato)metalate(III) salts. Salts 1 and 2 have each a global magnetic moment around μ ≈ 3 μB and are semiconductors with an energy gap of 2.5 eV each due to the d orbitals of the central metallic ion chromium(III) The evaluation of the antibacterial activities in vitro reveals that compounds 1 and 2 are active on the bacteria tested when the minimum inhibitory concentration (MIC) values are equal to 31.25 or 62.5 μg/mL, hence their potential therapeutic effect.