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

Here complexation of coumarin-3-carboxilic acid (HCCA) with Cr(III), Co(II), Ni(II), Cu(II) and Zn(II) at 37 °C and in 0.16 M NaClO4 is discussed. Speciation profiles obtained by potentiometric titrations show that in aqueous solution a complexation occurs at a ligand-to-Cr(III), -Ni(II) and -Cu(II) ratio of 1:1, and at a ligand-to-Co(II) and -Zn(II) ratio of 1:1, 2:1 and 3:1. For Co(II)-HCCA system also a polynuclear species is formed (i.e., Co2(OH)(CCA)2+). The coordination sites of HCCA to the different metal ions were determined with the aid of UV–Vis, IR and X-ray diffraction. Solid state chemistry of HCCA was enriched of two new X-ray resolved structures for cobalt and nickel metal cations, which are also reported and discussed. From crystal packing analysis results the intricate motif of weak interactions that leads to a supramolecular interesting arrangement, not yet disclosed and argued in the previous literature about coumarin-3-carboxilic acid isostructural coordination compounds.