Acta Phys. -Chim. Sin. ›› 2018, Vol. 34 ›› Issue (7): 830-836.doi: 10.3866/PKU.WHXB201712151

Special Issue: Toward_Atomically_Precise_Nanoclusters_and_Nanoparticles

• ARTICLE • Previous Articles    

Electronic Stability of Eight-electron Tetrahedral Pd4 Clusters

Yanfang SHEN1,Longjiu CHENG1,2,*()   

  1. 1 School of Chemistry and Chemical Engineering, Anhui University, Hefei 230601, P. R. China
    2 Anhui Province Key Laboratory of Chemistry for Inorganic/Organic Hybrid Functionalized Materials, Hefei 230601, P. R. China
  • Received:2017-10-31 Published:2018-03-26
  • Contact: Longjiu CHENG
  • Supported by:
    by the National Natural Science Foundation of China(21573001);the Foundation of Distinguished Young Scientists of Anhui Province, China


Motivated by the unusual structure of the [Pd4(μ3-SbMe3)4(SbMe3)4] cluster, which is composed of a tetrahedral (Td) Pd(0) core with four terminal SbMe3 ligands and four triply bridging SbMe3 ligands capping the four triangular Pd3 faces (J. Am. Chem. Soc. 2016, 138, 6964), we performed a computational study of the structure and bonding characteristics of the Td [Pd4(μ3-SbH3)4(SbH3)4] cluster and a series of its analogues. The Td structure of the [Pd4(μ3-SbH3)4(SbH3)4] cluster could be explained by the cluster electron-counting rules based on the 18-electron rule for transition-metal centers; each sp3 hybridized Pd atom contributed ten valence electrons, and eight valence electrons were provided by one terminal SbH3 and three bridging μ3-SbH3 ligands. The [Pd4(μ3-SbH3)4(SbH3)4] cluster had a count of 104 valence electrons in total; chemical bonding analysis indicated that the cluster featured twenty electron lone pairs generated by d orbital of the four Pd atoms, twenty-four Sb―H σ bonds, four terminal Pd―Sb σ bonds, and four delocalized bonds. There were two bonding patterns of the eight delocalized electrons between the four capping Sb atoms and the Pd4 core. The first pattern was based on the superatom-network (SAN) model, whereby the palladium cluster could be described as a network of four 2e superatoms. The second pattern was based on the spherical jellium model, whereby the cluster could be rationalized as an 8e [Pd4(μ3-SbH3)4] superatom with 1S21P6 electronic configuration. The density functional theory (DFT) calculations showed that the Td [Pd4(μ3-SbH3)4(SbH3)4] cluster had a large HOMO-LUMO (HOMO: highest occupied molecular orbital; LUMO: lowest unoccupied molecular orbital) energy gap (2.84 eV) and a negative nucleus-independent chemical shift (NICS) value (-12) at the center of the [Pd4(μ3-SbH3)4(SbH3)4] cluster, indicating its high chemical stability and aromaticity. Furthermore, the NICS values in the range of 0–0.30 nm of the [Pd4(μ3-SbH3)4] motifs were much more negative than those of [Pd4(SbH3)4] in the same range, revealing that the overall stability of [Pd4(μ3-SbH3)4(SbH3)4] was likely derived from the local stability of Pd4(μ3-SbH3)4. Meanwhile, the d10d10 interaction played a critical role in stabilizing the Pd4 tetrahedron structure, which is similar to the aurophilicity in Au-Au clusters. It was also found that there is a large difference in the stability of transition metal and non-transition metal clusters with a tetrahedron structure. The structures and bonding patterns of the designed analogues were similar to those of [Pd4(μ3-SbH3)4(SbH3)4]. To summarize, this study was relevant for deciphering the nature of the bonds in a tetrahedral complex with four cores and eight ligands, and predicting a series of analogues. It is expected that this work will provide more options for the synthesis of tetrahedral 4-core transition metal compounds.

Key words: Metal cluster, Super valence bond, Superatom, Chemical bonding analysis, Closed-shell interaction, Aromaticity