Synthesis, crystal structure, fluorescence and electrochemical properties of two Ag(I) complexes based on 2-(4′-pyridyl)-benzoxazole/SPPh3 ligands

To explore the luminescence properties of silver complexes in the solid state, two Ag(I) complexes, [Ag(4-PBO)2(NO3)] {di[2-(4′-pyridyl)-benzoxazole]silver(I) nitrate} (1) and [Ag2(SPPh3)4](ClO4)2 {[tetra(triphenylphosphine sulfide)disilver(I)] diperchlorate} (2) (4-PBO =2-(4′-pyridyl)-benzoxazole, SPPh3 = triphenylphosphine sulfide), have been synthesized and characterized by elemental analysis, FT-IR and UV-Vis spectroscopy. Single-crystal X-ray diffraction revealed that 1 is three-coordinate by two nitrogen atoms from two 4-PBO ligands and an oxygen atom from the coordinated nitrate anion forming a triangular plane configuration. In 2, the SPPh3 ligands adopt a monodentate coordinated and monoatomic bridging mode to connect two Ag(I) ions, resulting in a three-coordinate symmetrical binuclear structure. In the solid state, the luminescence properties of the ligands 4-PBO, SPPh3 and their complexes were investigated. The results demonstrated that 1 results in the fluorescence quenching of aggregates due to the strong π–π stacking effect. The fluorescence enhancement of 2 may be attributed to the "aggregation-induced emission" (AIE) effect of restricted intramolecular rotations of the peripheral phenyl rings against the central core. In addition, cyclic voltammograms of 1 and 2 indicated an irreversible Ag+/Ag couple.