Cluster–π electronic interaction in a superatomic Au₁₃ cluster bearing σ-bonded acetylide ligands

Abstract

An organometallic Au 13 cluster having two σ--bonded acetylide ligands was synthesized and its structure was determined by X--ray crystllography. Absorption spectral studies indicated the presence of the electronic coupling between the superatomic Au13 core and the acetylide π--orbitals, which was supported by theoretical considerations.Gold-acetylide sigma bonds have been of general interest as they bring about the emergence of unique optical properties and reactive intermediates in catalysis. [1][2][3][4][5][6][7][8][9] For simple metal complexes, rich chemistry has been explored from both functional and structural perspectives. On the other hand, although numerous ligand-protected gold clusters have been synthesized, 10-14 examples of alkynyl-ligated clusters have been quite rare to date, and the nature of the bonding and electronic interaction between a cluster kernel and a C≡C π-system has not been experimentally characterized. [15][16][17][18] Tsukuda et al. have observed no appreciable electronic interaction in the optical absorption spectra of alkyne-protected gold clusters of diameter > 1 nm. 15,16 We have also demonstrated a similar phenomenon for a structurally precise Au 8 cluster with an anisotropic core+exo-type structure. 17 Herein we report the first experimental evidence of electronic interaction between a polyhedral gold core and a σ-bonded π-unit in the absorption spectrum of a phenylethynyl-modified Au 13 cluster with an icosahedral geometry and superatomic 8-electron system. [19][20][21][22] We have also investigated its electronic structure based on DFT calculations, which support the presence of electronic interaction between the superatomic gold core and π-conjugated units.Regioselective introduction of two alkynyl ligands on the surface of the icosahedral Au 13 skeleton was achieved by the ligand-exchange reaction of a dichloro-substituted Au 13 cluster cation ([Au 13 (dppe) 5 Cl 2 ](PF 6 ) 3 , 1·(PF 6 ) 3 ), which was synthesized according to the HCl-mediated post-synthetic method. 20 The reaction cleanly proceeded by employing excess amounts of terminal alkynes and base (sodium methoxide), and the complete ligand exchange was verified by electrospray ionization mass spectrometry (ESI-MS) analysis of the reaction mixture. After workup, the crude product was recrystallized from acetonitrile and diethyl ether to give the pure dialkynylsubstituted cluster as its hexafluorophosphate salt ([Au 13 (dppe) 5 (C≡CPh) 2 ](PF 6 ) 3 , 2·(PF 6 ) 3 ), which was thoroughly characterized by ESI-MS analyses, elemental analyses, X-ray crystallography, and 1 H and 31 P NMR spectroscopies. For instance, the ESI mass spectrum of 2·(PF 6 ) 3 showed a set of signals around m/z 1585, in perfect agreement with the calculated isotope pattern for [Au 13 (dppe) 5 (C≡CPh) 2 ] 3+ (Fig. S2). Single-crystal X-ray analysis of 2·(PF 6 ) 3 revealed that the cluster core adopts an icosahedral geometry. Two alkynyl ligands are σ-coordinated to the two diagonal apexes (Au1 and Au1′) of the icosahedron from the trans positio...

Hydrogen bonds to Au atoms in coordinated gold clusters

“…However, the band positions were marked different. This observation implies the electronic perturbation effects of the neighbouring π-electrons of the phenylene bridges on the Au 6 moiety of 1 37, 38 , which may be correlated to its strong Au···H–C interactions. Although at present the possibility of through-space electronic coupling cannot be excluded, the above results may suggest interesting opportunities to tune the electronic structures and optical properties of gold clusters by proximal organic chromophore through non-covalent interactions.…”

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

“…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. [12][13][14][15] Furthermore,W ang et al have recently reported numerous homoleptic and heteroleptic alkynylprotected gold clusters,d emonstrating the formation of various surface Au I -acetylide motifs such as C C À Au À C C and C C À Au À C C À Au À C C. [16][17][18][19][20] These motifs are analogous to the staple units found in thiolate-protected clusters, but their capability to accommodate additional gold atoms through p-coordination should be noted. [1][2][3][4][5][6] Thiolates [1][2][3] and phosphines [6][7][8][9][10] have been frequently used as protecting ligands,w hile alkynyl (acetylide) ligands have recently emerged as unique and suitable ligands that stabilize gold clusters.…”

“…[1][2][3][4][5][6] Thiolates [1][2][3] and phosphines [6][7][8][9][10] have been frequently used as protecting ligands,w hile alkynyl (acetylide) ligands have recently emerged as unique and suitable ligands that stabilize gold clusters. [12][13][14][15] Furthermore,W ang et al have recently reported numerous homoleptic and heteroleptic alkynylprotected gold clusters,d emonstrating the formation of various surface Au I -acetylide motifs such as C C À Au À C C and C C À Au À C C À Au À C C. [16][17][18][19][20] These motifs are analogous to the staple units found in thiolate-protected clusters, but their capability to accommodate additional gold atoms through p-coordination should be noted. We have also introduced alkynyl ligands as coligands into Au 8 and Au 13 clusters and showed the substantial perturbation effects of particular p-electron systems on the electronic properties of the gold clusters.…”

The photoluminescence mechanism of ultra-small gold clusters

“…12 For some typical subnanometer-sized Au clusters, the optical properties are dramatically varied with different nuclearity or even with the same nuclearity due to their structural diversity. Although much effort has been made experimentally and theoretically, 5,[13][14][15][16][17][18][19][20][21][22][23][24][25][26][33][34][35][36][37][38][39][40]42 the dependence of optical properties on geometry, nuclearity and skeletal electron count (sec, i.e. Although much effort has been made experimentally and theoretically, 5,[13][14][15][16][17][18][19][20][21][22][23][24][25][26][33][34][35][36][37][38][39][40]…”