Multinuclear Ag Clusters Sandwiched by Pt Complex Units: Fluxional Behavior and Chiral-at-Cluster Photoluminescence.

Multinuclear Ag clusters sandwiched by Pt complex units were synthesized and characterized by single crystal X-ray diffraction and NMR studies. The sandwich-shaped multinuclear Ag complexes showed two different types of fluxional behavior in solution: rapid slippage of Pt complex units on the Ag3 core and a reversible demetalation-metalation reaction by the treatment with Cl anion and Ag ion, respectively. The Ag2 complex obtained by demetalation reaction from the Ag3 complex displayed U to Z isomerization. These multinuclear Ag complexes showed strong photoluminescence whose properties depended on the existence of Pt→Ag dative bonds. The Ag3 complex, identified to be "chiral-at-cluster", was optically resolved by the formation of a diastereomeric salt with a chiral anion. The enantiomers show circular dichroism (CD) and circularly polarized luminescence (CPL) properties which is unprecedented for compounds based on a chiral sandwich structure. Theoretical calculations allow to understand their structural features and photophysical properties.

A Heteropolynuclear Pt-Ag System Having Cycloplatinated Rollover Bipyridyl Units.

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.

U- to Z-shape isomerization in a Pt2Ag2 framework containing pyridyl-NHC ligands.

Synthesis and isomerization of a heteropolynuclear Pt2Ag2 complex containing pyridyl N-heterocyclic carbene (NHC) ligands are reported. The Pt2Ag2 complex could take two geometrical isomers possessing a twisted U-shaped structure and a Z-shaped structure. The rate of the isomerization reaction depended on the concentration of the solution, implying that the reaction took place through an intermolecular process.