[Ga-18(SitBu(3))(8)] and [Ga-22(SitBu(3))(8)] - Syntheses and structural characterization of novel gallium cluster compounds

The novel neutral gallium cluster compounds [Ga18R*(8),] (1) and [Ga22R*(8) ] (2) are obtained by warming up a metastable solution of gallium(I) bromid e in THF/C6H5CH3 after addition of equimolar amounts of supersilyl sodium N aR* from -78 degreesC to room temperature (R*-SitBu(3)-supersilyl). From X- ray structure analyses, the observed arrangements of the 18 and 22 Ga atoms in I and 2, respectively, are comparable with an 18 atom section of the be ta -Ga modification. or show at least some kind of relationship to a 22 ato m section of the Ga-III modification. This allows a description of both the clusters as metalloid. The topology of the Ga atoms in 2 is also well expl ained by the Wade-Mingos rules as an eightfold capped closo-Ga-14 cluster, whereby the Ga atoms of Ga-14 OCCUPY the center and the corners of a cuboct ahedron with one Ga-4, face replaced by a Ga-4 face. Some concepts are pres ented about the formation mechanism, the cluster growth, and the metalloid character of the two Ga cluster compounds.