Metal halide duster

The Nbg binary halides with seven electrons available for metal-metal bonding within the triangle are electron poor dusters. A simplified MO scheme suggests that the HOMO and LUMO possess metal d character. One unpaired electron is expected to be present. The existence of a low-lying metal cluster orbital is also indicated by the electronic spectra. 

The [MgXg] clusters found in the iodides Nbgln, [33] CsNbglu, [34] NbgIg(NR3)g, [35] and the unusual chain compound NbgLS [36] are rather an exception for the valence electron poor metal Nb. This type of duster however, is common with the (chalcogenide) halides of the more electron rich metals Mo [7, 9, 37, 38] and W as well as the (halide) chalcogenides of Re [7, 9, 39] and Tc. [40] There is a suffident number of d electrons in the dihalides of Mo and W to fill... 

Figure 5>3. Increasing connectivity of [M (X, X) dusters in halides, halide dialcogenides, and dialcogenides of the metals Nb, Mo, and Re. X links in a) RetSesClg (chain), b) MocOq (layer), and c) Nb In (network) X " links in d) Re5SegCl2 (layer) and e) MOjS6Br2 (network) X (+X ) links in f) Mo BrgSj (diain) and g) MoeBr S3 (layer). M, and X atoms are drawn with increasing size taken from ref. [6] (cf. Ikble 6-1 and text).

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