Synthesis, structures and optical properties of mononuclear La, Eu and Tb complexes supported by calix[4]arene ligands bearing three pendant salicylaldiminato arms

Abstract The synthesis and complexation behaviour of a new calix[4]arene ligand H 4 L3 bearing three pendant salicylaldimine arms towards selected lanthanide ions has been investigated. Reaction of H 4 L3 with Ln(NO 3 ) 3 ⋅6H 2 O in MeOH in the presence of NEt 3 provides monomeric complexes of composition [Ln(H L3 )] (Ln=La 3+ ( 4 ), Eu 3+ ( 5 ), Tb 3+ ( 6 )). An X‐ray crystallographic analysis for 4 reveals that only two of the three ligand arms are involved in the coordination of the lanthanide ions, to give eight‐coordinated Ln 3+ ions in a distorted square‐antiprismatic N 2 O 6 environment. UV‐vis spectrophotometric titrations show that such monomeric species prevail in CH 2 Cl 2 /MeOH (1/1 v/v) solution. The apparent stability constants determined by UV‐vis spectrophotometric titration are log K =6.8(2) for 5 and log K =5.8(1) for 6 . The Eu and Tb complexes luminesce only weakly at 77 K with luminescence lifetimes of 0.469 and 0.306 s.