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, <b>1</b>; C₆H₄OMe-3, <b>2</b>) or the anionic trinuclear Pt₂Pb cluster (NBu₄)­[{Pt­(bzq)­(CCC₆H₄CF₃-4)₂}₂­{Pb­(HBpz₃)}], <b>3</b>, stabilized by Pt–Pb and Pb^II···η²-(CCR) bonding interactions in the solid state, as confirmed by X-ray crystallography. The variable-temperature ¹H NMR spectra of <b>3</b> 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 <b>1</b> and <b>2</b> indicate that in solution these dimers generate mainly binuclear [{Pt­(bzq)­(CCR)₂}­{Pb­(HBpz₃)}] units by cleavage of the Pb^II···η²-(CCR) interactions. All clusters exhibit phosphorescent emission in rigid media (solid, glasses) and <b>3</b> also in CH₂Cl₂ solution. The emission maxima of <b>1</b> and <b>2</b> 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 <b>3</b> coincides with that of its precursor, indicating little or no involvement of the Pt–Pb bonds in the emissive state