Using vibrational and electronic spectroscopies to investigate different complexes in the formamide/nickel chloride system

Raman, IR and UV–vis–NIR experiments of formamide (FA) and nickel chloride solutions at different compositions were carried out. The quantitative Raman study at the νCN region shows that 5 FA molecules are coordinated to Ni (II) and the sixth position of the octahedron is occupied by one chloride, with preferential formation of [Ni(FA)5Cl]Cl in concentrations near 0.1 mol kg−1. In higher concentrations the [Ni(FA)4Cl2] complex becomes the most abundant. The downshift of the νCO mode of FA was evidenced by the appearance of a new band at 1640 cm−1 in the IR spectra of the most concentrated salt solutions. Also, the downshift of the δOCN mode combined with the upshift of the νCN vibration have allowed us realize that Ni (II) is coordinated by the O atom of FA. The d orbital splitting (Δo) has been directly determined from the electronic spectrum of the [Ni(FA)6]Cl2 complex and FA has been included in the spectrochemical series.

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