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.