2022 Volume 79 Pages 58-67
Homo- and heteropolynuclear transition-metal complexes are expected to show specific interactions and cooperative effects between metal atoms, providing novel functions that are unobtainable from mononuclear complexes. For example, Pt(III) and Pd(III), unusual oxidation states of Pt and Pd, are stabilized by forming polynuclear complexes through Pt−Pt and Pd−Pd bond formation. Pyrazole and its derivatives are interesting ligands which often act as bridging ligands, and a variety of coordination modes are known for them. We have developed various types of Pt-based heteropolynuclear complexes with pyrazolate bridges, whose emission energies can be controlled by the change of incorporated group 11 metal ions. Luminescence is one of the best indices to investigate the metal-metal interactions in heteropolynuclear complexes, because it is sensitive to the change of energies of ground and excited states. The pyrazolate bridged Pt2Ag2 complexes having N^C and C^C chelate ligands show isomerization between U- and Z-shaped geometrical isomers in solution. These complexes can be converted to the corresponding Pt2Ag3 complexes, which are stabilized by Pt→Ag dative bond. The Pt2Ag3 complex having Ph-NHC chelating ligands, 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.
