Polarographic Behavior of 1, 4, 8, 11-Tetraazacyclotetradecane in Acetonitrile

Abstract

1, 4, 8, 11-tetraazacyclotetradecane(cyclam) gave two anodic waves (1:1) (E_1/2=-0.35 and -0.52V) in acetonitrile containing 0.1mol dm^-3 R₄NClO₄ (R=Et or Bu) or 0.05mol dm^-3Me₄NClO₄ as the supporting electrolyte at 25°C. With 0.1mol dm^-3 NaClO₄, the potential difference between two waves became small (E_1/2=-0.325 and -0.465V), and finally, with 0.1mol dm^-3 LiClO₄, the two waves were combined into a single anodic wave at E^1/2=-0.225V. The anodic waves of cyclam (L) with R₄NClO₄ were based on successive mercury dissolution reactions: L⁺Hg_??_[HgL]⁺_??_[HgL]²⁺. The process was reversible: the [HgL]²⁺ complex gave two cathodic waves on the DME at the same potential as the anodic waves from cyclam. The single anodic wave from cyclam in the presence of Li⁺ ions was attributed to the reaction: [LiL]⁺+Hg_??_[HgL]²⁺+Li⁺. The formation constant of [LiL]+ was evaluated (Li⁺+L_??_[LiL]⁺, log K=ca. 6.0) indirectly by the shift of the cathodic half-wave potential of [HgL]²⁺ to a positive direction with increasing concentration of Li⁺. Other voltammetric techniques, such as cyclic voltammetry or differential pulse polarography and coulometry, were also employed to elucidate the electrochemical process.