Size-selective formation of tungsten cluster-containing silicon cages by the reactions of Wn+ (n=1-5) with SiH4

The reactions of tungsten clusters, W-n(+) (n = 1-5), with silane and their sequential reactions were investigated using FTICR mass spectrometry. It was found that the Si or SiH2 addition to the clusters, accompanied by H-2 release, occurred for every collision with silane and then suddenly stopped at the specific silicon atom numbers of m: m = 12 for n = 1, m = 17 and 18 for n = 2, m = 22 for n = 3, m = 25 and 26 for n = 4 and m = 29 for n = 5. These values coincide with the surrounding atom numbers of a simple close packing model, suggesting the formation of stable silicon cages encapsulating tungsten clusters. (C) 2004 Elsevier B.V. All rights reserved.