Unusual Attractive Au–π Interactions in Small Diacetylene‐Modified Gold Clusters

Abstract

It is well knownt hat alkynes act as p-acids in the formation of complexes with metals.W efound unprecedented attractive Au-p interactions in diacetylene-modified [core + exo]-type [Au 8 ] 4+ clusters.The 4-phenyl-1,3-butadiynyl-modified cluster has unusually short Au-C a distances in the crystal structure,r evealing the presence of attractive interactions between the coordinating C Cm oieties and the neighboring bitetrahedral Au 6 core,w hich is further supported by IR and NMR spectra. Suchweak interactions are not found in monoacetylene-modified clusters,w hichi ndicates that they are specific for diacetylenic ligands.T he attractive Au-p interactions are likely associated with the low energy of the p*orbital in the diacetylenic moieties,into which the valence electrons of the gold core may be backdonated. The [Au 8 ] 4+ clusters show clear red-shifts of > 10 nm with respect to the corresponding mono-acetylenic clusters in UV/Vis absorption bands,w hich indicates substantial electronic perturbation effects of the Au-p interactions.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi. Figure 5. Aromatic region of the 1 HNMR spectra of a) 1a,b)1b, c) 1c,d)2a,a nd e) 2b,measured in CD 2 Cl 2 /CD 3 OD (1:1) at 25 8 8C. Asterisks indicate signals assignable to p-Ph1 (d = 7.0 ppm) and m-Ph1 (d = 6.8 ppm). As tructure explaining the Ph-group labeling is also shown.