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.Ligand-protected gold clusters with adefined nuclearity and geometrical structure have attracted considerable interest regarding their application in optoelectronic materials and catalysis. [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. [4] Unlike thiolates and phosphines,w hich only have a s-bonding coordination character,t he p-systems of acetylide ligands can act as both s-a nd p-donors to gold atoms,e nabling the formation of various coordination motifs on the cluster surface.T he first example of such alkynyl-protected gold clusters is Au 54 (C CPh) 26 ,r eported by Tsukuda et al. in 2012, [11] but crystal structure determination was not achieved. 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. [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. Such diverse coordination modes of alkynyl ligands are unique features that are not found for conventional s-only type ligands and therefore they expand the scope and aspects of molecular gold clusters.In the examples mentioned above,m ono-acetylenic ligands,s uch as phenylethynyl, have been used as protecting ligands.Herein we show that diacetylenic (1,3-diynyl) ligands (C C À C C À R) have unusual interaction activities with gold frameworks,w hich were firmly identified from X-ray cry...

Toward Controlling the Electronic Structures of Chemically Modified Superatoms of Gold and Silver

“…[ 124 ] As a result, the oblate superatoms with an electron configuration of (1S) 2 (1P) 4 become stable due to the closure of the electronic shell, [ 124 ] as can be found in Au 7 (6e), [ 125,126 ] Au 8 (6e), [ 34 ] and the crown‐shaped Au 9 (6e) [ 29,127–131 ] ( Table 6 ). In contrast, the prolate superatoms with an electron configuration of (1S) 2 (1P) 2 become stable, as can be found in Au 6 (4e) [ 132–140 ] and Au 7 (4e) [ 141–143 ] (Table 6). The magic stability of the prolate superatoms with n * = 14 such as Au 20 (14e), [ 144,145 ] Au 23 (14e), [ 146,147 ] Ag 23 (14e), [ 75 ] and Au 25 (14e) [ 148 ] can be explained by the electronic shell closure with an electron configuration of (1S) 2 (1P) 6 (1D) 6 .…”

“…[ 98–100,103 ] These examples convince us that a unique class of quasi‐molecules can be developed by bonding various superatomic units via various bonding schemes. [ 75,98–120,135–154 ]…”

Effect of Gold(I) on the Room‐Temperature Phosphorescence of Ethynylphenanthrene

“…The packing of 1 a , 1 e , and 2 a complexes in the solid state displays a zig‐zag conformation driven by the establishment of π⋅⋅⋅π (both between the phenanthrene and the π ring of the triphenylphosphane and between two phenanthrene rings), C−H⋅⋅⋅π interactions, and Au⋅⋅⋅π [42] in the case of 1 – 2 a (Figures S33–S37 in the Supporting Information). The two ethynylphenanthrene groups in 1 e are located in an antiparallel disposition and the resulting 3D packing displays the presence of inner cavities.…”

Not Only Hydrogen Bonds: Other Noncovalent Interactions

“…In a recent paper, it is written: "It is well known that alkynes act as π-acids in the formation of complexes with metals" [25]. If this were correct, then the bond should be a tetrel one; on the other hand, if the alkyne was the base and the metal (in this case Au) the Lewis acid [14], the bond would be a regium bond.…”