Coordination-triggered redox activity of early and late lanthanide calix[4]arene complexes

Abstract

The methylation of p-tert-butylcalix[4]arene in the distal 1,3-phenolic sites provides H₂L = {p-tert-butylcalix[4](OMe)₂(OH)₂arene}. This unit acts as a rigid coordinating ligand to early and late lanthanide metal ions, enabling the construction of two families of mononuclear compounds featuring (N(nBu)₄)[Ln^IIIL(acac)₂]·CH₃CN (Ln = Pr (1), Nd (2), Ho (3), and Er (4)) and (N(nBu)₄)₂[Ln^IIIL{Mo₅O₁₃(OMe)₄(NO)}]·CH₂Cl₂ (Ln = Nd (5) and Er (6)). The metal ions adopt distorted bicapped trigonal prismatic coordination environments, resulting in slow relaxation of the magnetization for 4. These compounds exhibit reversible redox waves at positive potentials, centered within the calix[4]arene ligand, representing a new type of calix[n]arene-based electrochemical activity induced by coordination to the metal centers.