Structural and Photophysical Study on Alkynyl Cyclometalated Pt2Pb2 and Pt2Pb Clusters

Neutralization reactions of (NBu4)­[Pt­(bzq)­(CCR)2] (bzq = 7,8-benzoquinolinyl) with [Pb­(HBpz3)]­Cl (pz = pyrazolyl) afford tetranuclear neutral Pt2Pb2 derivatives [{Pt­(bzq)­(CCR)2}­{Pb­(HBpz3)}]2 (R = Ph, 1; C6H4OMe-3, 2) or the anionic trinuclear Pt2Pb cluster (NBu4)­[{Pt­(bzq)­(CCC6H4CF3-4)2}2­{Pb­(HBpz3)}], 3, stabilized by Pt–Pb and PbII···η2-(CCR) bonding interactions in the solid state, as confirmed by X-ray crystallography. The variable-temperature 1H NMR spectra of 3 confirm the existence of a dynamic equilibrium that averages the “Pt­(bzq)­(CCC6H4CF3-4)2” groups in solution. 1D 1H PGSE-NMR, 2D DOSY, and 1H variable-temperature NMR experiments for the tetranuclear clusters 1 and 2 indicate that in solution these dimers generate mainly binuclear [{Pt­(bzq)­(CCR)2}­{Pb­(HBpz3)}] units by cleavage of the PbII···η2-(CCR) interactions. All clusters exhibit phosphorescent emission in rigid media (solid, glasses) and 3 also in CH2Cl2 solution. The emission maxima of 1 and 2 are slightly blue-shifted in relation to the precursors, being assigned to a mixed 3MLCT/3LC (L = bzq) excited state, perturbed by the Pt–Pb bond. However, the emission maximum of 3 coincides with that of its precursor, indicating little or no involvement of the Pt–Pb bonds in the emissive state.