Synthesis, catalase, superoxide dismutase and antitumour activities of copper(II) carboxylate complexes incorporating benzimidazole, 1,10-phenanthroline and bipyridine ligands: X-ray crystal structures of [Cu(BZA)2(bipy)(H2O)], [Cu(SalH)2(BZDH)2] and [Cu(CH3COO)2(5,6-DMBZDH)2] (SalH2=salicylic acid; BZAH=benzoic acid; BZDH=benzimidazole and 5,6-DMBZDH=5,6-dimethylbenzimidazole)