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Reversible Binding of Solvent to Naked Pb II Centers in Unusual Homoleptic Alkynyl‐Based Pt 2 Pb 2 Clusters
Author(s) -
Berenguer Jesús R.,
Fernández Julio,
Gil Belén,
Lalinde Elena,
Sánchez Sergio
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201303665
Subject(s) - homoleptic , chemistry , crystallography , luminescence , intramolecular force , solvent , delocalized electron , metal , acetone , tetrahydrofuran , molecule , photochemistry , stereochemistry , materials science , organic chemistry , optoelectronics
We report a series of luminescent sandwich‐type clusters [Pt 2 Pb 2 (C≡CR) 8 ] (R=Tol, 1 ; C 6 H 4 OMe‐3, 2 ; C 6 H 4 OMe‐4, 3 ) with a dynamic Pt 2 Pb 2 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 Pt 2 Pb 2 /C≡CR nature, with a predominant lead contribution and Pb⋅⋅⋅Pb bonding character ( 3 MLCCT/ 3 IL). 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(Me 2 CO), 2 ( acetone ) 3 , and 2 ( THFMe ‐ 2 ) 2 allow the vapochromic responses to be ascribed to the fast creation/disruption of solvate clusters [Pt 2 Pb 2 (C≡CR) 8 S x ] ( x ≥2), with concomitant electronic and geometrical modifications within the Pt 2 Pb 2 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 Pb 2+ 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 ⋅CH 2 Cl 2 and 3 ⋅2 CH 2 Cl 2 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.