Platinum(II) Complexes of Tridentate N∧N- ∧N -Coordinating Ligands Based on Imides, Amides, and Hydrazides: Synthesis and Luminescence Properties

Abstract

Five Pt(II) complexes are described in which the metal ion is bound to anionic (Formula presented.) -coordinating ligands. The central, deprotonated N atom is derived from an imide Ar−C(=O)−NH−C(=O)−Ar {PtL1–2Cl; Ar=pyridine or pyrimidine}, an amide py−C(=O)−NH−CH2−py {PtL3Cl}, or a hydrazide py−C(=O)−NH−N=CH−py {PtL4Cl}. The imide complexes PtL1–2Cl show no significant emission in solution but are modestly bright green/yellow phosphors in the solid state. PtL3Cl is weakly phosphorescent. PtL4Cl is formed as a mixture of isomers, bound through either the amido or imino nitrogen, the latter converting to the former upon absorption of light. Remarkably, the imino form displays fluorescence in solution, λ0,0=535 nm, whereas the amido shows phosphorescence, λ0,0=624 nm, τ=440 ns. It is highly unusual for two isomeric compounds to display emission from states of different spin multiplicity. The amido-bound PtL4Cl can act as a bidentate (Formula presented.) -coordinating ligand, demonstrated by the formation of bimetallic complexes with iridium(III) or ruthenium(II).