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

The reactions of tungsten clusters, Wn+ (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 H2 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.