First Copper(II) Indole Carboxylate Complexes: Features of Synthesis, Structural Organization, and Biological Activity

Complexes [Cu2(ind)4(EtOH)2] (I), [Cu(ind)2bpy]·1.15MeCN·0.85MeOH (II), and [Cu(ind)(phen)2]+ ·ind–·0.5Hind·1.5H2O (III) were synthesized using slow diffusion of the starting solutions of copper(II) acetate, indole-2-carboxylic acid (Hind), and oligopyridines (2,2'-bipyridine (bpy)/1,10-phenanthroline (phen)). The structures of the complexes were established by single crystal X-ray diffraction and the phase purity was confirmed by powder X-ray diffraction. According to single-crystal X-ray diffraction data, I and II are molecular complexes, while III is an ionic complex comprising the cationic mononuclear [Cu(ind)(phen)2]+ moiety in the independent part of the unit cell and the ind– anion in the outer sphere. The coordination environment of copper(II) cation (C.N.Cu 5) is described by a square pyramid (I, III) or a planar square with C.N.Cu 4 (II). The supramolecular level involves both hydrogen bonds and non-covalent interactions, mainly of the π…π and C–H…π type. The stability of salt solutions of I–III was studied by spectrophotometry in comparison with the free ligands and over a period of 2 days. Complexes I–III were investigated for biological activity: the antimycobacterial activity was evaluated against the non-pathogenic Mycolicibacterium smegmatis strain and the cytotoxicity of III was assessed against the test human ovarian adenocarcinoma cells (SKOV3).