Experimental and theoretical vibrational spectroscopic investigation of Zn(II) halide complexes of 3-aminopyridine and 3-chloropyridine

The aim of this study is to analyse the influence of the formation of metal–ligand bond through the ring nitrogen on the vibrational wavenumbers of pyridine derivatives, depending on the electron releasing (NH2) or electron withdrawing (Cl) substituent, in the same position. As pyridine derivatives, 3-aminopyridine (3apy) and 3-chloropyridine (3Clpy) were used. Moreover, determination of the wavenumbers of metal–ligand bond vibrations has a separate interest. In order to investigate the influence of the counter ligand, halide, on pyridine derivative vibrations, calculations were carried out on both Zn(L)2Cl2and Zn(L)2Br2 (where L = 3-aminopyridine or 3-chloropyridine) compounds. Full assignment of the spectra is proposed and the analysis of the experimental data are supported by DFT calculations performed with B3LYP functional and the 6-311++G(d,p) basis set. The FT-IR (400–4000 cm−1) and Raman (100–3200 cm−1) spectra of compounds are recorded and are compared with that of the calculated spectra. Anharmonic corrections to the harmonic wavenumbers are done with the same method and level of theory. The coordination effects on vibrational wavenumbers of 3apy and 3Clpy were discussed by comparing the spectra of free and coordinated molecules.