Discrete Di‐ and Tetranuclear Silver Complexes Based on <i>ortho</i>‐Imino‐ or <i>ortho</i>‐Amino‐methylpyridyl‐Appended <i>p‐tert</i>‐Butylcalix[4]arene or <i>p‐tert</i>‐Butylthiacalix[4]arene in 1,3‐Alternate Conformation

Abstract

Four new multivalent ligands 5 – 8 derived from calix[4]arene and thiacalix[4]arene backbones in 1,3‐alternate conformation bearing ortho ‐imino‐ and ortho ‐amino‐methylpyridine chelating sites have been designed, prepared and characterized. Owing to the imposed 1,3‐alternate conformation of the backbone, ligands 5 – 8 offer two coordinating pockets composed of two sets of chelates located above and below the mean plane of the macrocyclic framework. Ligands 6 – 8 , independent of the nature of the anion associated with the Ag + cation (AgX; X = BF 4 – , PF 6 – , SbF 6 – , AsF 6 – , NO 3 – ), form dinuclear silver complexes in solution and in the solid state. Ligand 7 , in the presence of an excess of Ag + , also forms tetranuclear silver complexes 7 ‐(AgBF 4 ) 4 and 7 ‐(AgNO 3 ) 4 in the presence of two different auxiliary ligands (H 2 O or NO 3 – ) that have been characterized in the solid state. Due to a rather short Ag–Ag distance of about 2.89 Å, the tetranuclear complex 7 ‐(AgBF 4 ) 4 is emissive in the solid state, at 298 K ( λ exc = 295 nm, λ em = 425 nm), which results from argentophilic interactions between the closely positioned silver cations.