Synthesis, electrochemistry and luminescence of [Pt{4′-(R)trpy}(CN)]+(R = Ph, o-CH3C6H4, o-ClC6H4or o-CF3C6H4; trpy = 2,2′:6′,2″-terpyridine): crystal structure of [Pt{4′-(Ph)trpy}(CN)]BF4·CH3CN

The synthesis and characterization of [Pt{4′-(R)trpy}(CN)]X (R = Ph, X = BF4 or SbF6; R = o-CH3C6H4, X = SbF6; R = o-ClC6H4, X = SbF6; or R = o-CF3C6H4, X = SbF6) are described where trpy = 2,2′:6′,2″-terpyridine. Single crystals of [Pt{4′-(Ph)trpy}(CN)]BF4·CH3CN were grown by vapour diffusion of diethyl ether into an acetonitrile solution of [Pt{4′-(Ph)trpy}(CN)]BF4. An X-ray crystal structure determination of the solvated complex confirms the near linear coordination of the cyanide ligand to the platinum centre. The cation is almost planar as evidenced by a twist of only 1.9° of the phenyl group out of the plane of the terpyridyl moiety. Cyclic voltammograms were recorded in DMF/0.1 M TBAH for the [Pt{4′-(R)trpy}(CN)]+ cations. Two quasi-reversible one-electron reduction (cathodic) waves are observed with E1/2 values that show the trend expected for an increasingly lower energy of the trpy-based LUMO of the complex i.e., [Pt{4′-(Ph)trpy}(CN)]+ ∼ [Pt{4′-(o-CH3C6H4)trpy}(CN)]+ < [Pt{4′-(o-ClC6H4)trpy}(CN)]+ < [Pt{4′-(o-CF3C6H4)trpy}(CN)]+. All the [Pt(4′-(R)trpy}(CN)]+ cations are photoluminescent in dichloromethane. Emission by [Pt{4′-(Ph)trpy}(CN)]+ is from an excited state with largely 3MLCT orbital parentage, but with some intraligand 3π–π* character mixed-in (τ = 0.1 µs). In contrast, the other three cations display emission that appears exclusively intraligand 3π–π* in origin (τ ∼ 0.8 µs). Emission spectra have been recorded in a low concentration frozen DME {1 : 5 : 5 (v/v) DMF–MeOH–EtOH} glass. For the R = o-CH3C6H4, o-ClC6H4 and o-CF3C6H4 cations the envelope of vibronic structure and energies of the vibrational components are essentially the same as that recorded in dichloromethane. However, for the [Pt{4′-(Ph)trpy}(CN)]+ cation, there is a blue-shift in the energies of the vibrational components as compared to that recorded in dichloromethane, as well as a change in the envelope of vibronic structure to a more “domed” pattern; this has been interpreted in terms of a higher percentage of intraligand 3π–π* character in the emitting state for the glass. Increasing the concentration of the glass invariably leads to aggregation of the cations and the consequent development of new low energy bands, such that at 0.200 mM broad peaks centred at ca. 650 and 700 nm dominate the spectrum; these bands are assigned to excimeric 3π–π* and 3MMLCT emission, respectively.