On the Metal-Ion-Coordinating Properties of the Benzimidazolate Residue in Aqueous Solution – Extent of Acidification of Benzimidazole-(N3)H Sites by (N1)-Coordinated Divalent Metal Ions

✍ Scribed by Larisa E. Kapinos; Helmut Sigel

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 238 KB
• Volume: 1999
• Category: Article
• ISSN: 1434-1948
• DOI: 10.1002/(sici)1099-0682(199910)1999:10<1781::aid-ejic1781>3.0.co;2-h

✦ Synopsis

The stability constants of the 1:1 complexes formed between reveals that the stabilities of the M(L-H) + complexes are significantly enhanced, as one might have expected due to Mg 2+ , Mn 2+ , Co 2+ , Ni 2+ or Cd 2+ (= M 2+ ) and the anionic 5(6)nitrobenzimidazolate [= (NBI-H) -] or 5,6-dinitrobenzimi-the negative charge present on the ligands. Of course, the electron-withdrawing properties of (N3)-bound metal ions dazolate [= (DNBI-H) -] were determined by potentiometric pH titrations in aqueous solution (25 °C; I = 0.5 M, NaNO 3 ).

facilitate the release of the proton from the (N1)H site in the M(NBI) 2+ and M(DNBI) 2+ complexes, if compared to the The acidity constants for the deprotonation of the (N1)H sites in neutral NBI and DNBI (= L) were measured by the same situation in the free ligands. The effect of a metal ion bound to a benzimidazolate or imidazolate residue on the method. The comparison of the stability constants determined for the M(L-H) + complexes with those calculated coordination tendency toward a further metal ion (giving rise to an imidazolate bridge) was estimated. from log K M ML versus pK H HL straight-line plots, which were established recently for neutral benzimidazole-type ligands, H(BI) ϩ , occurs with pK H H(BI) ϭ 5.63 [12] and the formation