Synthesis, characterization and luminescence properties of homoleptic platinum(ii) acetylide complexes

Abstract

A family of homoleptic tetraalkynylplatinate(II) complexes (NBu₄)₂[Pt(CCR)₄] containing various arylsubstituted (R = C₆H₄X), where X is an electron-donating, -withdrawing or -delocalizing substituent, and ethynylpyridine (C₅H₄N-2, C₅H₄N-4) ligands have been prepared. The structures of complexes with R = (4-CF₃)C₆H₄ (4·2HCCl₃), (4-CN)C₆H₄ (6·H₂O) and C₅H₄N-4 (9b·HCCC₅H₄N-4·2H₂O) have been determined by single-crystal X-ray diffraction. While in the case of 4 two molecules of CHCl₃ are incorporated to the anion by short CH⋯π interactions, for the para-pyridylethynyl derivative one H₂O molecule connect different anions through moderate N⋯H–O–H⋯N intermolecular interactions, giving an extended one-dimensional chain. The photophysical and electrochemical properties of the complexes have been examined. All of them display emissions at 77 and 298 K in the fluid and solid state, with lifetimes in the microsecond regime. In some cases the emission profile is clearly the envelope of several closely bands, whose relative intensity depends on the excitation energy. On the basis of TD-DFT theoretical calculations on the anion [Pt{CC(4-CN)C₆H₄}₄]²⁻ of complex 6, it is proposed that the emissions are due to triplet intraligand excited states, with both an aryl (or pyridyl) and acetylenic character, which arise from an admixture of π → π*(CCR) IL and d_π(Pt) → π*(CCR) MLCT transitions.