Theoretical Exploration of Peculiar Sandwich-Type Clusters Formed by the Coordination of E (E = Si, Ge, Sn) Zintl Clusters: Structural Properties, Active Sites, and Hydrogen Storage.

A peculiar heterogeneous metal sandwich fragment {(Ge)[η-Ge(PdPPh)]} anion cluster was synthesized for the first time by Xu et al. (Xu, H. L.; Tkachenko, N. V.; Wang, Z. C.; Chen, W. X.; Qiao, L.; Munoz-Castro, A.; Boldyrev, A. I.; Sun, Z. M. , , 5286). In this work, novel analogous sandwich compounds ({(E)[η-E(PdPH)]} (E = Si (), Ge (), Sn ()) were studied using quantum chemical calculations and wave function analysis to determine the geometry, bonding nature, aromaticity, active sites, and hydrogen storage. Structural analysis revealed that the clusters were compounds formed by the coordination of two E (E = Si, Ge, Sn) Zintl clusters with a central E@Pd (E = Si, Ge, Sn) interlayer. The steric hindrance at both ends is small, facilitating facile attachment to other molecules. The valence states of the central atom E (E = Si, Ge, Sn) are close to zero, indicating that they are stable novel heterometallic sandwich compounds, and the Zintl ligands at both ends are negative, thus they can react with Lewis acids. Bonding analysis showed that the E (E = Si, Ge, Sn) cluster has a delocalized framework bonding mode. For aromaticity analysis, we used AdNDP, ELF, LOL, ICSS, and NICS to qualitatively and quantitatively clarify that these clusters possess the characteristics of overall delocalization, σ aromaticity, and remarkable stability. By analyzing the unique structure and predicting the reaction sites, we concluded that the E ligand reacts with Lewis acids. Finally, through the adsorption of hydrogen molecules, the average adsorption energies of - were 0.387, 0.374, and 0.325 eV per H molecule, respectively, meeting the physical adsorption standard, with the adsorption effect of being slightly more superior than that of and . Our study represents a substantial step forward in the study of high-density materials for volumetric H storage applications.