Octagold selenido nanoclusters:Significance of surface ligands on tuning geometric and electronic structure of Au8Se2 kernel

摘要

Two diphosphine-protected superatom gold selenido nanoclusters,[Au_(8)Se_(2)(dppm)4]^(2+)(SD/Au_(8)a,dppm=Ph_(2)PCH_(2)PPh_(2))and[Au_(8)Se_(2)(dppe)4]^(2+)(SD/Au_(8)b,dppe=Ph_(2)P(CH_(2))2PPh_(2)),were obtained by the reduction of[Au(SMe2)Cl]in the presence of Ph3PSe as the selenium ion releasing agents.Both can be regarded as“superatoms”with 1S^(2)configuration based on the spherical Jellium model.Despite the same metal-ligand binding motifs on the surface and the intrinsic C_(2)molecular symmetry,the configurations of Au_(8)Se_(2)kernels in them are different in terms of Au-Au bonded metallic frameworks.SD/Au_(8)a displays a heart-shaped[core+exo]type structure(Au4 tetrahedron core+two exo Au2Se units),whereas the two exo Au_(2)Se counterparts in SD/Au_(8)b are additionally locked by an obvious Au-Au bond,forming a distorted hexagonal Au6 ring with two capping AuSe units appended above and below it.Consequently,they showed different photophysical properties as reflected by their electronic absorption and emission spectra.Especially,both SD/Au_(8)a and SD/Au_(8)b exhibit blue-shifted thermochromic luminescence upon cooling from 293 to 83 K but the latter exhibits anomalous emission intensity evolution trends due to the occurrence of temperature-induced phase transition as revealed by varied-temperature crystallographic analyses.This work not only clearly illustrates the significance of ligands on tuning the kernel structure but also provides two rarely comparable examples for better understanding of the structure-property relationship of gold nanoclusters.