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Cyclometallated Pt(II) Complexes Containing a Functionalized Bis-Urea Alkynyl Ligand: Probing Aggregation Mediated by Hydrogen Bonds versus Pt⋅⋅⋅Pt and π−π Interactions
European Journal of Inorganic Chemistry  (IF2.524),  Pub Date : 2021-07-20, DOI: 10.1002/ejic.202100499
Gaëtan Basuyaux, Anissa Amar, Claire Troufflard, Abdou Boucekkine, Rémi Métivier, Matthieu Raynal, Jamal Moussa, Laurent Bouteiller, Hani Amouri

Neutral cyclometallated Pt(II) complexes [(C^Nt−Bu^Nt−Bu)Pt−R] (45) containing a bis-urea alkynyl (R) ligand have been prepared and fully characterized. The dichotomous nature of 45 makes it difficult to anticipate which interactions (hydrogen bonds, π−π stacking and Pt⋅⋅⋅Pt) will dominate their assembly process. The aggregation properties of 45 were thus probed by multifarious analytical (UV/Vis, FT-IR, NMR, MS, CD, emission) and computational (DFT, TD-DFT) techniques. CD analyses of sergeants-and-soldiers type mixtures between 4 and an enantiopure Pt-free monomer (S,S)-3 reveal that no amplification of supramolecular helicity occurs in this system. In fact, complex 4 acts as competitor or chain capper, likely through hydrogen bonding, of the homochiral assemblies formed by (S,S)-3. In DMSO, 1H NMR and DOSY analyses indicate that 4 and 5 form aggregates. Likewise, the aggregation is promoted by the addition of H2O as suggested by red shift of the lowest energy emission band, which might originate from a 3MMLCT excited state. TD-DFT calculations confirm that self-aggregation occurs through Pt⋅⋅⋅Pt and π−π interactions yielding head-to-tail aggregates in DMSO and DMSO/H2O mixtures. Our study therefore suggests a (condition dependent) competitive rather than a cooperative mode of action of the different types of interactions present in aggregates of 45.