Luminescent Anionic Cyclometalated Organoplatinum (II) Complexes with Terminal and Bridging Cyanide Ligand: Structural and Photophysical Properties

Abstract

We present the synthesis and characterization of two series of mononuclear heteroleptic anionic cycloplatinated(II) complexes featuring terminal cyanide ligand Q⁺[Pt(C^N)(<i>p</i>-MeC₆H₄)(CN)]^- [C^N = benzoquinolate (bzq), Q⁺ = K⁺ <b>1</b> and NBu₄⁺ <b>4</b>; 2-phenylpyridinate (ppy), Q⁺ = K⁺ <b>2</b> and NBu₄⁺ <b>5</b> and 2-(2,4- difluorophenyl)pyridinate (dfppy), Q⁺ = K⁺ <b>3</b> and NBu₄⁺ <b>6</b>] and a series of symmetrical binuclear complexes (NBu₄)[Pt₂(C^N)₂(<i>p</i>-MeC₆H₄)₂(μ-CN)] (C^N = bzq <b>7</b>, ppy <b>8</b>, dfppy <b>9</b>). Compounds <b>5</b>, <b>6</b>, and <b>7</b>-<b>9</b> were further determined by single-crystal X-ray diffraction. There are no apparent intermolecular Pt···Pt interactions owing to the presence of bulky NBu₄⁺ counterion. Slow crystallization of K[Pt(ppy)(<i>p</i>-MeC₆H₄)(CN)] <b>2</b> in acetone/hexane evolves with formation of yellow crystals, which were identified by single-crystal X-ray diffraction methods as the salt complex {[Pt(ppy)(<i>p</i>-MeC₆H₄)(CN)]₂K₃(OCMe₂)₄(μ-OCMe₂)₂}[Pt(ppy)(<i>p</i>-MeC₆H₄)(μ-CN)Pt(ppy)(<i>p</i>-MeC₆H₄)]·2acetone (<b>10</b>), featuring the binuclear anionic unit <b>8^-</b> neutralized by an hybrid inorganic-organometallic coordination polymer {[Pt(ppy)(<i>p</i>-MeC₆H₄)(CN)]₂K₃(OCMe₂)₄(μ-OCMe₂)₂}⁺. The photophysical properties of all compounds were recorded in powder, polystyrene film, and solution states with a quantum yield up to 21% for <b>9</b> in the solid state. All complexes displayed bright emission in rigid media, and for the interpretation of their absorption and emission properties, density functional theory (DFT) and time-dependent DFT calculations were applied.