Photoelectron Spectroscopy of Lanthanide-Silicon Cluster Anions LnSin- (3 ≤ n ≤ 13; Ln = Ho, Gd, Pr, Sm, Eu, Yb): Prospect for Magnetic Silicon-Based Clusters

Photoelectron spectroscopy was utilized to study a variety of LnSi(n)(-) cluster anions (Ln = Yb, Eu, Sm, Gd, Ho, Pr; 3 <= n <= 13). For a particular size n, the measured valence electronic transitions of all these systems fall into either one of two categories, reflecting the influence of the different oxidation states of the lanthanide atoms involved. In one, the spectra of YbSin- and EuSin- are nearly identical to each other, while in the other the spectra of GdSin-, HOSin-, and PrSin- are essentially identical. SMSin- clusters exhibit an intermediate behavior with smaller clusters resembling the former category and larger clusters resembling the latter category. In the intermediate size range, 7 <= n <= 10, for SMSin- both categories appear to be present, with one matching the EuSin--Iike systems and the other HoSin--like clusters. The distinction between LnSin- categories strongly correlates with the oxidation state of the particular lanthanide as usually found in its compounds. On the basis of this observation, we conclude that, among the Ln-silicon clusters studied herein, Yb, Eu, and in case of Sm, sizes n >= 10, adopt a nominal +2 oxidation state while Ho, Pr, Gd, and in case of Sm, sizes n <= 7, exhibit a nominal +3 oxidation state. Furthermore, dramatic increases in adiabatic electron affinity values observed at n = 10 for the Ln(III)Si(n) series and at n = 12 for the Ln(II)Si(n) series were attributed to an inherent electronic stabilization of those particular clusters, rather than to the lanthanides' encapsulation. The observed limited effect of f-electrons on the valence electronic structure and thus on bonding in LnSin- clusters may leave these electrons available for inducing magnetism. Consequently, Ln@Si-n clusters-may hold promise as building blocks of silicon-based cluster materials with magnetic properties.