Synthesis, crystal structure and solid state photoluminescence of [Pt(trpy)(C≡CPh)]SbF6 (trpy=2,2′:6′,2"-terpyridine)

The synthesis a and characterisation of an orange polymorph of [Pt(trpy)(C CPh)]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 center dot center dot center dot Pt distances of 3.604(l) and 4.412(l) angstrom. The perpendicular distances between successive cation planes are constant along the stack at a value of 3.33 angstrom. 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)(C CPh)]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 [lambda(em)(max) = 637 nm at 80 K]. We assign the >= 200 K emission as (MLLCT)-M-3 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 (MMLCT)-M-3 emission, suggesting that the phase change leads to d(z2) (Pt)-d(z2) (Pt) orbital interactions. Of particular interest is that the cation exhibits (MLCT)-M-3 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. (c) 2006 Elsevier B.V. All rights reserved.