Abstract
Coordination chemistry of benzimidazole and 2-substituted benzimidazole derivatives towards transition metal ions is reviewed. Benzimidazole complexes containing halides or carboxylates derivatives are discussed, as well as the coordination chemistry of 2-substituted benzimidazoles bearing additional nitrogen, oxygen or sulfur atoms as potential binding sites, which may form chelates. The latter ligands give place to a variety of metal-ligand coordination modes. In some cases, these bidentate ligands favour the formation of a six membered ring, by inclusion of a metal ion in a planar delocalized system. Some of the studied 2-substituded benzimidazoles include 2-uroyl, 2-carbamate, 2-benzothiazole, 2-(2-benzothiazolylamino)benzothiazole, 2-(2- aminobenzothiazolyl-amino) benzoxazole, 2-(4'-thiazolyl)benzimidazole, 2-((5-methylpyrazol-3- yl)methyl)benzimidazole, 2-guanidinobenzimidazole, 2-aminomethylbenzimidazole, 1- (benzimidazol-2-yl)phenolato, 2-(2-benzimidazol-2-yl)pyridine-N-oxide-N,O and N- (benzothiazol-2-yl)-dithiocarbamic methyl ester. It is important to mention that benzimidazole and its derivatives promote intra and inter-molecular interactions, such as hydrogen bonding and π- stacking, giving place to the formation of molecular aggregates.
Highlights
The biological activity and pharmacological properties of the benzimidazole derivatives, have led us to investigate the coordination behavior of benzimidazole and benzothiazole derivatives towards transition metal ions
The compound dichloro-bis(1H-benzimidazole)-cobalt(II), reported Barba-Behrens et al, is an example is of this type of complexes, where the two chlorine ions (Cl-) and two benzimidazoles are bonded to the metal center through the unprotonated nitrogen, Figure 1.18a
The tetranuclear copper(II) complex [Cu4Cl6O(bz)4]·2C2H5OH was first reported by Tosik and later by Xu.21a, 21b In this compound, each metal ion is in a distorted trigonal bipyramid geometry bonded to three equatorial chloride atoms, one benzimidazole in an axial position, and the fifth position is occupied by the central oxygen atom O1, Figure 4
Summary
Compounds with fumaric and succinic acid, catena-((μ2-fumarato-O,O')-diaqua-bis(1Hbenzimidazole-N)-M(II)) (M(II) = cobalt,25a nickel,25b copper,25c), and catena-((μ2-succinatoO,O')-diaqua-bis(1H-benzimidazole-N)-M(II)) (M(II) = cobalt,25a and copper,25c), were obtained from the corresponding acid in alkaline medium These compounds consist of a polymeric MII complex bridged by fumarato or succinato dianions, each carboxyl group is bonded in a monodentate mode to the metal atom and it is bonded to a neighboring metal ion through terminal carboxyl groups forming one-dimensional polymeric chains, Figure 7. Dimeric copper(II) compounds have been obtained with acetate bridges by BukowskaStrzyzewska33a and, with methacrylate by Zhou and co-workers.33b The coordination complexes have a dimeric copper arrangement through four carboxylate bridges, while the benzimidazole ligands are coordinated in the axial position, giving place to an octahedral arrangement for each copper(II) ion, Figure 15 Another type of a dimer was stabilized by the oxyacetate derivative in compound bis(μ2-. This structure is analogous to that of its cobalt(II) derivative.36c a Figure 18. (a) (1H-benzimidazole)-(aqua)-(iminodiacetato-N,O,O')-copper(II); (b) tris(1Hbenzimidazole)-(iminodiacetato-N,O,O')-nickel(II).36a, 36b
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