Syntheses, crystal structures, chirality and aggregation-induced phosphorescence of stacked binuclear platinum(ii) complexes with bridging Salen ligands

Abstract

A novel class of cyclometalated binuclear Pt(ii) complexes, [(C^N)Pt(μ-Salen)Pt(C^N)] (C^N = 2-phenylpyridine or benzo[h]quinoline, Salen = N,N′-bis(salicylidene)ethylenediamine), have been synthesized and characterized. Owing to the blockage of intramolecular rotation in the bridging Salen ligands, all the double-layer stacked complexes exhibit strong aggregation-induced phosphorescence with quantum yields up to 0.35 through well-tuned intramolecular Pt-Pt interactions (3.37-4.48 Å) and strong multiple intermolecular interactions, such as H-H, C-H, O-H, Cl-H, and Pt-H interactions. Interestingly, if chiral Salen ligands are adopted, it is facile to prepare (R,R)/(S,S) enantiopure Pt(ii) complexes, which were characterized by X-ray diffraction, circular dichroism spectra and time-dependent density functional theory calculations. This is the first example of stacked binuclear Pt(ii) complexes with well-known tetradentate Salen ligands as bis-bidentate-bridging ligands and would render a new structural motif for bridging ligands and chiral binuclear complexes.