Synthese et caracterisation de complexes metalliques avec le ligand 2,2'-biimidazole et son derive 1,1'-dimethyl-2,2'-biimidazole

A large variety or new complexes of zinc, cadmium and chromium have been prepared from the reactions of the corresponding salts with the ligand 2,2'-biimidazole (H2biim). The reaction of H2biim with Cd(BF4) 2 led to the formation of the tris-chelate compound [Cd(H2biim) 3]2(SiF6)(BF4)2·6EtOH. The [Cd(H2biim)3]2+ and SiF6 2- ions define an extended hydrogen-bonded network, in which the B F- ions surrounded by disordered ethanol molecules occupy large cavities.;The reaction of Zn(ClO4)2 with Me2biim produced the dinuclear compound [(Me2biim)Zn(mu-Me2biim) 3Zn(Me2biim)](ClO4)4, containing two monodentate and three bridging Me2biim ligands bonded to Zn atoms in a distorted tetrahedral environment. A related neutral (NO3) 2Cd(mu-Me2biim)3Cd(NO3)2 complex containing only bridging Me2biim ligands was also synthesized. The coordination around each Cd atom is a distorted octahedron containing one monodentate and one bidentate nitrato ligands. Two ionic trinuclear Cd(II) compounds were also obtained, which include two sets of three bridging Me 2biim ligands connecting a central Cd atom to two terminal Cd centers. An extra Me2biim ligand is chelated to each terminal metal and the sixth coordination site is occupied by aqua ligands in the symmetric [(Me 2biim)(H2O)Cd(mu-Me2biim)3Cd(mu-Me 2biim)3Cd(CH2OH)(Me2biim)] (ClO 4)6 complex, whereas one aqua ligand is replaced by a methanol ligand in the non-symmetric [(Me2biim)(H2O)Cd(mu-Me 2biim)3Cd(mu-Me2biim)3Cd(CH 3OH)(Me2biim)] (ClO4)6 compound. In the chelating ligands, dihedral angles of ∼38° between the two imidazole rings reduce the repulsion between the N-methyl groups, but considerable strain remains, as evidenced from one of the Cd--N bond being much longer than the other. In the various compounds, dihedral angles of 60-80° are found between the two imidazole rings in the bridging ligands.;A dinuclear complex [Cu2(Me2biim)4(H 2O)2](NO3)4 in which two Cu(II) centers are bridged by four Me2biim ligands was also isolated. Each of these bridging ligands provides one N donor to each Cu center, generating the base of an approximate square pyramid, whose apical position is occupied by an aqua ligand. The nitrate ions and uncoordinated water molecules form a network of hydrogen bonds, in which the aqua ligands are also involved.(Abstract shortened by UMI.).;The tris-chelate [Cr(H2biim)3](NO3) 3 complex was obtained by reacting CrCl3·3THF with [Ag(H2biim)](NO3) in methanol. In the solvent-free material, each ligand forms two N--H···O bonds to a nitrate ion and generates locally neutral [Cr(H2biim)3](NO 3)3 units. A methanol solvate was also obtained, in which intermolecular interactions involve optimal use of the hydrogen-bonding ability of the [Cr(H2biim)3]3+ cations, NO 3- anions and methanol molecules. In both cases, there is no long-range regular organization of the different units. Deprotonation of [Cr(H2biim)3](NO3)3 with NaOCH 3 yielded the neutral compound Cr(Hbiim)3. Its powder X-ray diffraction pattern is similar to that of Ru(Hbiim)3, suggesting that it also consists of mutually perpendicular interlocked honeycomb sheets. Recrystallization by slow diffusion of diisopropyl ether into a methanol solution yielded a porous material of composition Cr(Hbiimh)3·2.6C 6H14O, in which superposed honeycomb sheets create infinite channels (∼ 13 A diameter) filled with disordered solvent molecules. A totally different structure was adopted by the solvate Cr(Hbiim)3·C 6·2H2O, where the benzene molecules are encapsulated in a cavity created by five completed molecules.