Ways of enhancement of biological efficiency of copper(ii) and zinc(ii) complexes: synthetic and structural aspects, thermal properties, and antimycobacterial activity

The reactions of copper(ii) and zinc(ii) acetates with anions of 5-phenylfuran-2-carboxylic acid (Hphfur) and 5-nitro-1,10-phenanthroline (nphen) or 2,2′-bipyridine (2,2′-bpy) in the MeOH/MeCN system afforded mononuclear complexes of the composition [Cu(phfur)₂(nphen)H₂O] (1) and [Zn(phfur)₂(2,2′-bpy)]•H₂O (2). The structures of these complexes were determined by X-ray diffraction analysis (XRD). According to the XRD data, the copper atom in molecular complex 1 is in a distorted square-pyramidal environment (S_Q(CuN₂O₃) = 0.68); the zinc atom in molecular complex 2, in a distorted trigonal-bipyramidal environment (S_Q(ZnN₂O₃) = 3.87). The supramolecular level of 1 is mediated by intermolecular π–π interactions between the aromatic moieties of the ligands and represents a 3D supramolecular structure. in the structure of 2, the water molecules of crystallization are involved in intermolecular hydrogen bonds, resulting in the formation of centrosymmetric hydrogen-bonded dimers. The supramolecular level of 2 is mediated by C—H⋯O and C—H⋯π interactions. According to the simultaneous thermal analysis, complexes 1 and 2 are characterized by different types of thermal destruction. Thus, the explosophoric groups in the ligands of compound 1 are responsible for an intense exothermic effect. The results of biological assays show a certain correlation between the type of the substituted moiety in the heterocycle and the activity against the non-pathogenic Mycolicibacterium smegmatis strain.