σ Aromaticity of the Bimetallic Au₅Zn⁺ Cluster

Abstract

Experimental and theoretical evidence for a "sigma aromatic" bimetallic cluster is presented. A mass spectrometric analysis of AuNZn+ (N = 2-44) photofragments shows Au5Zn+ to be very abundant, proving its high stability. Calculations predict that Au5Zn+ has a planar geometry and six valence s electrons occupying delocalized sigma-bonded molecular orbitals in a manner similar to that of aromatic organic compounds, except for their nodal properties in the molecular plane. The delocalized sigma electrons provide diamagnetic ring currents, suggesting Au5Zn+ is aromatic.

The Cu7Sc Cluster is a Stable σ‐Aromatic Seven‐Membered Ring

“…This indicates that, similar to the previously reported Au 5 Zn + cluster, [10] the aromaticity is due to the MOs composed mainly of the 4s AOs of copper and scandium, and this confers s-aromatic character to Cu 7 Sc.…”

“…[9] An energetically low-lying five-membered cyclic cluster of Au 5 Zn + was recently reported to be s-aromatic, based on the electron count and the NICSs. [10] The B 6 C 2À dianion was demonstrated to be a six-membered boron ring with a planar hexacoordinated carbon atom at the center. [11] Compounds having D 7h point group symmetry are rare.…”

Four Decades of the Chemistry of Planar Hypercoordinate Compounds

“…In 2003, Lievens and co-workers [133] prepared Au 5 Zn + clusters ( Figure 54) by cationic photo-fragmentation mass spectrometry.T hey detected planar tetracoordinate Au,a nd planar tetra/pentacoordinate Zn motifs stabilized by s aromaticity. Planar tetracoordinate and pentacoordinate motifs in Ag 5 X 0,AE (X = Sc, Ti,V ,Cr, Mn, Fe, Co,and Ni) [134] and Au 5 X + (X = Au,S c, Ti,C r, Fe) [135] clusters were investigated by Lievens,Nguyen and co-workers.Frenking and co-workers [136] found that because of the strong electron delocalization, iron can adopt planar pentacoordination in FeSb 5 + and FeBi 5 + in D 5h symmetry as local minima but not global minima on the potential-energy surface.F urthermore,p lanar pentacoordinate uranium in neutral U@[c-U 5 (m 2 -C) 5 ]molecule (23 f)was predicted by Tsipis and co-workers, [60] which extends the planar motifs from transition metals into actinoids.B ut, it is not clear if this structure is ag lobal minimum or not.…”

Far‐Infrared Spectra of Yttrium‐Doped Gold Clusters AunY (n=1–9)

“…Up to now, numerous studies on doped gold clusters have been carried out, with dopant atoms ranging from nonmetallic elements (S, P, Si, Se…) [10,[16][17][18][19][20][21][22][23] to alkali metals (Li, Na…) [21,24,25] and transition metals (Sc, Ti, V…). [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] Small Au n S clusters [16] were calculated to exhibit planar structures and their geometry can be constructed by replacing one Au atom of the Au n + 1 cluster by a S atom, while from n = 6 on, the doped cluster adopts a 3D structure. Au 5 S was predicted to have higher stability than its neighbors.…”

“…Subsequently, the Au 5 Zn + cation was reported to be the first example of a saromatic bimetallic cluster, which was proposed to cause its enhanced stability. [27] The properties of Au n M with n = 2-7 and M = Ni, Pd, and Pt have been studied theoretically. [28] The planar structures are again favorable for all the clusters studied, except for Au 7 Ni, for which the most stable 3D structure turns out to be almost degenerate with its corresponding 2D form.…”