Experimental and Computational Studies of Alkali-Metal Coinage-Metal Clusters

摘要

Coinage and alkali metal mixed clusters,M_4Na~-(M = Cu,Au)have been investigated experimentally using photoelectron spectroscopy and computationally at correlated ab initio levels.The related Cu_4Li~-,Ag_4Li~-,Ag_4Na~-,and Au_4Li~-clusters as well as the neutral Cu_4Li_2 and Cu_4Na_2 clusters have also been studied computationally.The calculations show that the two lowest isomers of the negatively charged clusters include a pyramidal C_(4w)structure and a planar C_(2v)species.For Cu_4Li~-and Cu_4Na~-,the C_(4v)structure is calculated at correlated ab initio level to be 30.9 and 16.9 kJ/mol below the planar C_(2v)isomer,whereas the planar isomers of Au_4Li~-and Au_4Na~-are found to be 29.7 and 49.4 kJ/mol below the pyramidal ones.For Ag_4Li~-and Ag_4Na~-,the pyramidal isomers are the lowest ones.Comparison of the calculated and measured photoelectron spectra of Cu_4Na~-and Au_4Na~-shows that the pyramidal Cu_4Na~-cluster of C_(4v)symmetry and the planar Au_4Na~-of C_(2v),symmetry are detected experimentally.Calculations of the magnetically induced current density in Cu_4Li~-and Cu_4Li_2 using the Gauge-Including Magnetically Induced Current(GIMIC)method show that strong ring currents are sustained mainly by the highest-occupied molecular orbital primarily derived from the Cu 4s.The GIMIC calculations thus show that the Cu_4~(2-)ring is sigma-aromatic and that the d orbitals do not play any significant role for the electron delocalization effects.The present study does not support the notion that the square-planar Cu_4~(2-)is the first example of d-orbital aromatic molecules.