Crystal structures, theoretical calculations, spectroscopic and electrochemical properties of Cr(III) complexes with dipicolinic acid and 1,10-phenantroline

The crystal structures of compounds Na[Cr(dipic)2] · 2H2O (1) and [Cr(dipic)(phen)Cl] · 1/2H2O (2), dipic = dipicolinate, phen = 1,10-phenantroline, were determined. In both complexes, Cr(III) is in a distorted octahedral environment. In complex (1), the metal is coordinated to two nearly perpendicular dipic anions acting as tridentate ligands through one oxygen of each carboxylate group and the pyridinic nitrogen atom. In complex (2), Cr(III) ion is similarly coordinated to a dipic anion, defining a ligand equatorial plane. The phen molecule bridges the remaining equatorial coordination site and one of the axial positions through its N-atoms. The other axial position is occupied by a chloride ion.The optimized geometries of both compounds and their corresponding harmonic vibrational frequencies were calculated using methods of density functional theory. The infrared, Raman and electronic spectra of the complexes were recorded. Assignments of the most characteristic bands are reported and discussed. Their electrochemical properties were also investigated. Both compounds exhibit similar redox behavior; they undergo two main reduction processes involving the metal center and the dipicolinato ligand. No Cr(III) oxidation processes were found.

Graphical abstractThe synthesis and physicochemical study of two chromium compounds of stoichiometry Cr[(dipic)2] · 2H2O and [Cr(dipic)(phen)Cl] · 1/2H2O are presented. They were characterized by single crystal X-ray diffraction methods, FTIR, Raman, electronic spectroscopy and cyclic voltammetry. Theoretical calculations were also performed. The optimized geometries were compared with crystallographic data. The experimental spectra were assigned with the help of calculated frequencies.Figure optionsDownload full-size imageDownload as PowerPoint slide