Study of Complexation of Alkyl-Substituted 2,2′-Dipyrrolylmethene with Lanthanide Salts by Electronic Spectroscopy

It has been found with the use of electronic spectroscopy that the reaction of alkyl-substituted 2,2'-dipyrrolylmethene with La(III), Pr(III), Sm(III), Dy(III), Ho(III), Er(IIII), and Yb(III) salts leads to the formation of tris(dipyrrolylmethene) complexes. Based on electronic absorption spectroscopy data and formation constants of lanthanide complexes, together with the earlier data, analysis of the nature of M-L bonds in 2,2'-dipyrrolylmethene chelates with p, d, and f elements has been performed. A correlation was found between the complex stability and the polarizing action of the complex-forming ion on the chromophore p system of dipyrrolylmethene, which allows one to classify these heterocyclic ligands with probes highly sensitive to the change in the ratio between the ionic and covalent contributions to coordination interactions.