Synthesis, crystal structure and solid state photoluminescence of [Pt(trpy)(Ctriple bond; length of mdashCPh)]SbF6 (trpy=2,2′:6′,2″-terpyridine)

The synthesis and characterisation of an orange polymorph of [Pt(trpy)(Ctriple bond; length of mdashCPh)]SbF6 is described where trpy = 2,2′:6′,2″-terpyridine. An X-ray crystal structure determination at 293 K reveals that the cations are planar and stacked head-to-tail with alternating Pt⋯Pt distances of 3.604(1) and 4.412(1) Å. The perpendicular distances between successive cation planes are constant along the stack at a value of 3.33 Å. Crystal structure determinations at 240 and 200 K show that reducing the temperature to 200 K has no significant effect on the cation arrangement. However, below 200 K there is a phase change that we have not been able to characterise, but which has an effect on the solid state photoluminescence exhibited by [Pt(trpy)(Ctriple bond; length of mdashCPh)]SbF6. Thus, whereas at temperatures of ⩾200 K, a broad peak with two components at ca. 566 and 597 nm is observed, below 200 K a longer wavelength peak develops that red-shifts as the temperature is lowered [λ (em)max = 637 nm at 80 K]. We assign the ⩾200 K emission as 3MLLCT in origin, since the X-ray data show that ligand–ligand (LL) and not metal–metal (MM) interactions are important at T ⩾ 200 K. On the other hand, the long wavelength emission observed below 200 K is typical of 3MMLCT emission, suggesting that the phase change leads to dz2(Pt)–dz2(Pt)dz2(Pt)–dz2(Pt) orbital interactions. Of particular interest is that the cation exhibits 3MLCT emission in dichloromethane that maximizes at 619 nm, i.e., the high temperature solid state emission occurs at a shorter wavelength, an unexpected result since intermolecular interactions in the solid usually cause the emission to occur at longer wavelengths. A possible explanation for this unexpected result is given.