Structural and Photophysical Study on Alkynyl Cyclometalated Pt2Pb2 and Pt2Pb Clusters

Neutralization reactions of (NBu4)[Pt(bzq)(C CR)(2)] (bzq = 7A-benzoquinolinyl) with [Pb(HBpz(3))]Cl (pz = pyrazolyl) afford tetranuclear neutral Pt2Pb2 derivatives [{Pt(bzq)(CE CR),}{Pb(HBpz(3))}](2). Ph, 1; C6H4OMe3, 2) or the anionic trinuclear Pt2Pb cluster (NBu4):[{Pt(bzq)-. (CT CC6H4CP3-4)(2)}(2){Pb(HBpZ(3))}], 3, stabilized by Pt Pb and Pb172-(C CR) bonding interactions in the solid state, as confirmed by X-ray crystallography. The variable-temper attire 1HNMR spectra of 3 confirm the existence of a dynamic equilibrium that averages the Pt(bzq)(C CC6H4CP3-4)2 groups in solution. 1D 1HPGSE-NMR, 2D DOSY, and 21-1 variable-temperature NMR experiments for the tetranuclear. clusters 1 and 2 indicate that in solution these dimers generate mainly binuclear [{Pt(bzq)(G=CR)2}{Pb(EIBPZ3)}] units by cleavage of the Pb-II center dot center dot center dot eta center dot(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 3.(MLCTLC)-L-3 = bzq) excited state, perturbed by the Pt Pb bond. However, the emission maximum of 3 coincides withthat of its indicating little or no involvement of the Pt Pb bonds in the emissive state.