Experimental insights on the coordination modes of coumarin-3-carboxilic acid towards Cr(III)-, Co(II)-, Ni(II)-, Cu(II)- and Zn(II): A detailed potentiometric and spectroscopic investigation in aqueous media

•Cr(III)-, Co(II)-, Ni(II)-, Cu(II)-, Zn(II)–coumarinic acid complexes was studied.•The stoichiometry of the complexes was determined by potentiometric measurements.•The coordination sites were defined by UV–VIS, IR and X-ray diffraction.•The chelation occurs through the lactone and the carboxylic oxygen.•Solid state chemistry of coumarinic acid was enriched of two new X-ray structures.