Reversible Binding of Solvent to Naked PbII Centers in Unusual Homoleptic Alkynyl‐Based Pt2Pb2 Clusters

We report a series of luminescent sandwich‐type clusters [Pt₂Pb₂(C≡CR)₈] (R=Tol, 1 ; C₆H₄OMe‐3, 2 ; C₆H₄OMe‐4, 3 ) with a dynamic Pt₂Pb₂ metallic core, which is key to their intriguing stimuli‐responsive photophysical properties. The solvent‐free solids 1 – 3 display an orange emission ascribed to charge transfer from Pt–alkynyl fragments to a delocalized orbital with mixed Pt₂Pb₂/C≡CR nature, with a predominant lead contribution and Pb???Pb bonding character (³MLCCT/³IL). They exhibit mechanical, color, and luminescence changes that are reversible and perceivable with the naked eye, which are attributed to small inter‐ and intramolecular structural modifications induced by gentle grinding. Interestingly, 1 and 2 also exhibit remarkable and fast reversible vapochromic responses to donor solvent vapors (acetone, THFMe‐2: yellow; NCMe: green, vs. dry solids: orange). The structures of 1(acetone)₂ ?2(Me₂CO), 2 ( acetone ) ₃ , and 2 ( THFMe ‐ 2 ) ₂ allow the vapochromic responses to be ascribed to the fast creation/disruption of solvate clusters [Pt₂Pb₂(C≡CR)₈S_x] (x≥2), with concomitant electronic and geometrical modifications within the Pt₂Pb₂ core, which are easily accessible through a slight change in the stereochemical activity of the lone pair. The binding of one (or two) solvent molecules to Pb²⁺ increases the Pb???Pb separation in the metallic core, causing a destabilization of the target orbital and larger energy gaps of the transitions. All the solvates exhibit remarkable rigidochromism upon a decrease in temperature, which is also associated with the gradual increase in the transannular Pb???Pb separation, as revealed by X‐ray crystallography of 1 ( acetone ) ₂ at different temperatures. Investigation of the crystal lattice of 1 ?CH₂Cl₂ and 3 ?2 CH₂Cl₂ further suggests that the lack of vapor stimuli response of complex 3 could be attributed to the presence of competitive additional secondary intermolecular Pb???O(OMe) contacts, which give rise to a more compact network built up from extended chains of clusters.