Cobalt(II), nickel(II) and zinc(II) coordination compounds derived from aromatic amines

The structural and spectroscopic characterization of coordination compounds of four aromatic amines derived from benzimidazole, 2-aminobenzimidazole (L1), 1-(S-methylcarbodithioate)-2-aminobenzimidazole (L2), 2-(2-aminophenyl)-1H-benzimidazole (L3) and 6,6-dimethyl-5H-benzimidazolyl[1,2-c]quinazoline (L4) are reported. Cobalt(II) [Co(L1)2(CH3COO)2] (1) and nickel(II) [Ni(L1)2(CH3COO)2] (2) acetate coordination compounds of L1 are discussed. The synthesis and the X-ray crystal structure of the new 1-(S-methylcarbodithioate)-2-aminobenzimidazole (L2) is informed, together with its cobalt(II) [Co(L2)2Cl2] (3), [Co(L2)2Br2] (4) and zinc(II) [Co(L2)2Cl2] (5), [Zn(L2)2Br2] (6) coordination compounds. In these compounds the imidazolic nitrogen is coordinated to the metal center, while the ArNH2 and the S-methylcarbodithioate groups do not participate as coordination sites. A co-crystal of L1 and L2 is analyzed. Structural analyses of the coordination compounds of L3 showed that this ligand behaves as a bidentate ligand through the aniline and the imidazole groups forming six membered rings in the cobalt(II) [Co(L3)Cl2] (7) and zinc(II) [Zn(L3)Cl2] (8) compounds, as well as the nickel(II) nitrate [Ni(L3)2(H2O)2](NO3)2 (9). The quinazoline L4 was produced by insertion of one acetone molecule and water elimination in L3, its X-ray crystal diffraction analysis, as well as that of its zinc(II) coordination compound [Zn(L4)2Cl2] (10), are discussed.

The syntheses and structural analyses of coordination compounds of amine benzimidazole derivatives are discussed.2-Aminobenzimidazole and 1-(S-methylcarbodithioate)-2-aminobenzimidazole, behave as monodentate ligands, where the ArNH2 group does not participate as coordination site for the metal centers. 2-(2-Aminophenyl)-1H-benzimidazole coordinates in a bidentate mode to the metal ions, the aniline group is assisted by the imidazolic nitrogen giving six membered rings; a condensation reaction occurred in acetone giving a ZnCl2 compound with the new ligand 6,6-dimethyl-5H-benzimidazolyl[1,2-c]quinazoline.Figure optionsDownload as PowerPoint slideHighlights
► 2-(2-Aminophenyl)-1H-benzimidazole gave a condensation reaction, giving a ZnCl2 compound with a new tetracyclic ligand.
► The aniline group and the imidazolic nitrogen are bound to the metal ion in the 2-(2-aminophenyl)-1H-benzimidazole compounds.
► In the 1-(S-methylcarbodithioate)-2-aminobenzimidazole compounds, the ArNH2 and the carbodithioate are not coordinated.