The influence of selected metals on the electronic system of biologically important ligands

The influence of (i) halogens, (ii) different alkaline cations, Li(I), Na(I), K(I), Rb(I) and Cs(I), and (iii) lanthanide cations, Pr(III), Nd(III), Dy(III) and Er(III) on the electronic structure of the aromatic ring as well as of the carboxylic anion of the substituted benzoic acids was investigated. Systematic change (decrease or increase) in the wavenumbers of selected bands along the F-->Cl-->Br-->I series was observed. This change correlates in linear fashion with a decrease in the ionic potential of the halogens. A shift of the selected bands along with the alkaline and the lanthanide metal series was also observed and correlated with the ionic potential of the metal. It was noticed that the increase in the ionic potential of halogen atoms causes a remarkable increase in the difference (Deltanu) between the wavenumbers of nuasym(COO-) and nusym(COO-). Among the halogens the ionic potential is the lowest for iodine and this substituent brings about maximal proximity of the asymmetric and symmetric bands of the carboxylic anion. The change of cation in the molecule causes a characteristic change in the difference (Deltanu) between the wavenumbers of nuasym(COO-) and nusym(COO-) as well. Along with the lanthanide series under study (Pr-->Nd-->Dy-->Er) this difference decreases, while between alkaline cations lithium broadens these bands to the highest degree. The influence of the alkaline and the lanthanide cations on the vibrational structure of the whole molecule was analysed and compared.