Comparative equilibrium and structural studies of new pentamethylcyclopentadienyl rhodium complexes bearing (O, N) donor bidentate ligands

Complex formation processes of the (O,N) donor ligands 6-methylpicolinic acid (6-Mepic), quinoline-2-carboxylic acid (2-QA) and 3-isoquinolinecarboxylic acid (3-iQA) with the organometallic moiety (eta(5)-pentamethylcyclopentadienyl) rhodium(III) (RhCp*) were studied in aqueous solution by the combined use of pH-potentiometry, H-1 NMR spectroscopy and UV-Vis spectrophotometry. The solid phase structures of the [RhCp*(L)Cl] complexes bearing 6-Mepic and 2-QA were characterized by single-crystal X-ray diffraction analysis. Studies revealed the exclusive formation of mono complexes of the form [RhCp*(L)(H2O)](+)(L = deprotonated form of the ligands) and [RhCp*(L)(OH)]. The positively charged aqua species predominate at physiological pH even in the micromolar concentration range. The H2O/Cl- co-ligand exchange constants showed that all complexes preferably retain the chlorido ligand at the third coordination site at chloride ion concentrations present in the serum. In addition in vitro cytotoxicity of these [RhCp*(L) Cl] complexes was evaluated in three human cancer cell lines (A549, SW480 and CH1/PA-1) where they showed minor cytotoxic potency. (C) 2017 Elsevier B.V. All rights reserved.