Synthesis and electropolymerization of bis(4-cyano-1-pyridino)alkanes: effect of co- and counter-ions

The six new bis(4-cyano-1-pyridino)alkanes derivatives with different alkyl chain length (n = 2-6) and cyanometallate anions ([Fe(CN)6]3−, [Сo(CN)6]3−, [Fe(CN)4(CNH)2]2− and [Fe(CN)6]4−) have been synthesized and characterized by 1H-NMR, single-crystal X-ray analysis and UV–vis spectroscopy. The electroreduction of the obtained compounds under potentiostatic conditions (E1 = −0.75 V) and further electrode stabilization at E2 = 0 V resulted in the deposition of polyviologen films. The current efficiency of electropolymerization was found to increase with varying the counter anion in the row: [Fe(CN)6]3− < Br− < [Сo(CN)6]3−∼ [Fe(CN)6]4−. Analysis of cyclic voltammograms and EDX data demonstrated the simultaneous incorporation of [Fe(CN)6]4− and K+ ions into poly(pentyl-viologen) film during electropolymerization, and further expulsion of K+ ions during the film stabilization at E2 = 0 V. The electropolymerization efficiency was found to increase with increasing the alkyl chain length, resulting in the formation of polyviologen film with higher content of dimer form of viologen cation radical.