Synthesis, X-ray crystal structures and biomimetic and anticancer activities of novel copper(II)benzoate complexes incorporating 2-(4′-thiazolyl)benzimidazole (thiabendazole), 2-(2-pyridyl)benzimidazole and 1,10-phenanthroline as chelating nitrogen donor

Cu(BZA)2(EtOH)0.5 (1) was generated by the reaction of copper(II) hydroxide with benzoic acid (BZAH). [Cu(TBZH)2(BZA)](BZA) · 0.5TBZH · H2O (2) and [Cu(2-PyBZIMH)(2-PyBZIM)(BZA)] · 1.66EtOH (3) were obtained when 1 reacted with Thiabendazole (TBZH) and 2-(2-pyridyl)benzimidazole (2-PyBZIMH), respectively. [Cu(BZA)2(phen)(H2O)] (4) was isolated from the reaction of benzoic acid and 1,10-phenanthroline (phen) with copper(II)acetate dihydrate. Molecular structures of 2, 3 and 4 were determined crystallographically. 2 and 3 are hydrogen bonded dimers and trimers, respectively. The copper centres in complexes 2 and 3 are bis-chelate derivatives that have N4O ligation and their geometry is very similar being approximately square-pyramidal. However whereas in complex 2 both TBZH ligands are neutral in 3 one of the 2-PyBZIMH chelators is deprotonated on each copper. The structural results for 4 represent a re-examination of this crystallographically known compound for which no hydrogen atom coordinates have been previously reported. It crystallises as a hydrogen bonded dimmer and is a mono-chelate of phen with each copper centre possessing N2O3 ligation and square pyramidal geometry. The catalase and superoxide dismutase (SOD) activities of the four complexes along with those of the known phenanthroline complexes [Cu(mal)(phen)2] and [Cu(phendione)3](ClO4)2 (malH2 = malonic acid and phendione = 1,10-phenanthroline-5,6-dione) were investigated. Complexes 1–4, the metal free ligands and a simple copper(II) salt were assessed for their cancer chemotherapeutic potential against the hepatocellular carcinoma (Hep-G2) and kidney adenocarcinoma (A-498) cell lines. TBZH, 2-PyBZIMH and benzoic acid when uncoordinated to a metal centre offer poor chemotherapeutic potential. copper(II) benzoate is significantly more active than the free acid. The bis-chelate derivatives [Cu(TBZH)2(BZA)](BZA) · 0.5TBZH · H2O (2) and [Cu(2-PyBZIMH)(2-PyBZIM)(BZA)] · 1.66EtOH (3) elicit a significant cytotoxic response to the cancer cell lines tested. Replacing TBZH and 2-PyBZIMH with phen to give [Cu(BZA)2(phen)(H2O)] (4) does not significantly increase the anti-cancer activity.