EPR studies of copper(II) complexes with poly-2-methyl-5-vinyl-pyridine and poly-2-vinylpyridine

Cu(II) complexes of poly-2-vinylpyridine (P2VP) and poly-2-methyl-5-vinylpyridine (P2M5VP), partially quaternized by dimethylsulphate, and of the analogues (2-methyl-5-ethylpyridine, 2-ethylpyridine) were studied by EPR spectroscopy in a mixture of methanol and water. Peculiarities of the complex formation reaction were observed for the polymers compared to the analogues. At ratios of [Py]:[Cu²⁺] > 40, the predominant formation of tetrapyridinate-Cu(II) species [(CuL₄)]²⁺ was found for P2M5VP. However, differences were found between the parameters of EPR-spectra for the [CuL₄]²⁺ in the polymer from that of the [Cu(2M5EPy)₄]²⁺. It was suggested that, in the polymer, [CuL₄]²⁺ complexes with structure intermediate between square planar and tetrahedral are formed. Moreover, the maximum value of the pyridine fraction forming [CuL₄]²⁺ in P2M5VP was found to be about 10% and it is appreciably less the value of the fraction in P4VP (about 40%). For P2VP at [Py]:[Cu²⁺] > 40, an insignificant amount of [CuL₁]²⁺ and [CuL₂]²⁺ are formed in the solution. It follows that the main chain position relative to the ligand nitrogen atom in these polyvinylpyridines affects profoundly the complexation between the macromolecules and Cu(II) ions. The steric hindrances due to the chain are likely to change the [CuL₄]²⁺ structure and to prevent complex formation for P2VP.