Photophysical Responses in Pt₂Pb Clusters Driven by Solvent Interactions and Structural Changes in the Pb^II Environment

Two types of Pt₂Pb luminescent clusters were successfully prepared by the reaction of [Pt­(C₆F₅)­(bzq)­(OCMe₂)] (<b>1</b>) and [Pt­(C₆F₅)­(ppy)­(dmso)] (<b>2</b>) with [Pb­(SpyR-5)₂] (R = H, CF₃). Thus, whereas <b>5</b> (ppy, Spy) is generated through coordination of the pyridine-N atoms to the Pt centers, the formation of <b>3</b>, <b>4</b> (bzq), and <b>6</b> (ppy, SpyCF₃) is accompanied by a formal thiolate transfer from Pb^II to Pt^II, keeping the two N atoms in the primary environment of the lead. In <b>5</b>, the <i>neutral</i> Pb center adopts a rather stable and symmetrical “Pt₂S₂” coordination sphere supplemented by two Pb··F_<i>o</i> contacts, whereas for the remaining species several pseudopolymorphs were found depending on the solvent (<b>3</b>, <b>4</b>) and crystallization conditions (<b>6</b>). This structural diversity relies on changes in the coordination mode of the SpyR ligands (μ-κ<i>S</i>,<i>N</i>/μ-κ³<i>S</i>,<i>N</i>,<i>S</i>), intermetallic Pt–Pb bonds, and secondary <i>intra-</i> and <i>intermolecular</i> contacts induced by Pb–solvent binding. Notably, the changes, which entail a slight tuning of the stereochemical activity of the lone pair, have also a remarkable impact on the emissive state (³L′CCT/³L′LCT, SpyR → Pb,Pt/(C^∧N) in nature). Clusters <b>3</b> and <b>4</b> display a distinct and fast reversible blue shift vapoluminescent response (<b>4</b> shows also color changes) to donor solvents, correlated with changes in the environment of the Pb^II ion (asymmetric <i>hemidirected</i> to more symmetric <i>holodirected</i>) upon solvent binding and, additionally, in <b>4</b> with modifications in the crystal packing, as confirmed by XRD and supported by TD-DFT calculations. <b>5</b> and <b>6</b> do not show a vapoluminescent response. However, for <b>6</b>, three different and interconvertible forms, a symmetrical form (yellow <b>6-y</b>) and two asymmetrical forms with a rather short Pt–Pb bond (pale orange <b>6·acetone</b> and orange <b>6-o</b>), exhibiting different emissions were found. Notably, slow crystallization and low concentration favor the formation of the <i>thermodynamically</i> more stable yellow form, whereas fast crystallization gives rise to orange solids with a remarkable red shift of the emission. Interestingly, <b>6</b> also exhibits reversible <i>mechanochromic</i> color and luminescence changes