A Heteropolynuclear Pt–Ag System Having Cycloplatinated Rollover Bipyridyl Units

Abstract

The synthesis and photophysical properties of the heteropolynuclear Pt-Ag complex having cyclometalated rollover bipyridine ligands (bpy*) and bridging pyrazolato ligands are reported. The Pt2Ag2 complex was synthesized by two step reactions from a Pt(II) complex precursor having the rollover bpy* ligand, [Pt(bpy*)(dmso)Cl], with 3,5-dimethylpyrazole (Me2pzH) and a subsequent replacement of NH protons in the Me2pzH moieties with the Ag(I) ion. The Pt2Ag2 complex exists as a mixture of U- and Z-shaped isomers in solution, whose structures were clearly determined by single-crystal X-ray structural analyses. NMR studies using the single crystals revealed rapid isomerization of the Pt2Ag2 complexes in solution, although the Pt2Ag2 structures were supported effectively by the multiple metal-metal interactions. Furthermore, the Pt2Ag2 framework can capture a Ag(I) ion during the U-Z isomerization to afford a Pt2Ag3 core with the formation of Pt → Ag dative bonds. The Pt2Ag3 complex showed further aggregation to form a dimer structure in the presence of coordinating solvent via the crystallization process. The formation of Pt → Ag dative bonds significantly changes the emission energy from the Pt2Ag2 complex, while the emission spectra of U- and Z-isomers of Pt2Ag2 complex almost coincide with each other and their emissive properties are very similar. The density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations revealed the effects of additional Ag(I) ion on the photophysical properties of the heteropolynuclear Pt-Ag complexes bearing the rollover bpy* ligands.