Discrete Di‐ and Tetranuclear Silver Complexes Based on ortho‐Imino‐ or ortho‐Amino‐methylpyridyl‐Appended p‐tert‐Butylcalixarene or p‐tert‐Butylthiacalixarene in 1,3‐Alternate Conformation
Four new multivalent ligands 5–8 derived from calixarene and thiacalixarene 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 = BF4 –, PF6 –, SbF6 –, AsF6 –, NO3 –), 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‐(AgBF4)4 and 7‐(AgNO3)4 in the presence of two different auxiliary ligands (H2O or NO3 –) 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‐(AgBF4)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. The formation of tetranuclear silver complexes in the solid state with short Ag–Ag distances displaying argentophilic interactions is described.
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