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

摘要

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-methyl-pyridine 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 angstrom, the tetranuclear complex 7-(AgBF4)(4) is emissive in the solid state, at 298 K (lambda(exc) = 295 nm, lambda(em) = 425 nm), which results from argentophilic interactions between the closely positioned silver cations.