Isoelectronic cluster

Carbon is known with all coordination numbers from 0 to 8 though compounds in which it is 3- or 4-coordinate are the most numerous. Some typical examples are summarized in the Panel (p. 291). Particular mention should also be made of hypercoordinate non-classical carbo-nium ions such as 5-coordinate CHj", square pyramidal CsHs (cf. the isoelectronic cluster B3H9, p. 154), pentagonal pyramidal C6Me6 " (cf. iso-electronic Bf,Hio, p. 154) and the bicyclic cation 2-norbomyl, C7H] 1... 

X-ray diffraction, which showed that the structure of the [Tc2Cl8]2 ions is analogous to that of the isoelectronic cluster rhenium and molybdenum chlorides and bromides with a quadruple M-M bond [1,89,90] (Fig. la, Table 1). 

If there is only one atom shared between two clusters (an unknown situation for B) then o = l. Thus, [(R2C2B4H4)2E], E = Ga , Ge, (Figure 2.19) exhibits a structure consisting of two pentagonal pyramids fused at one apical vertex occupied by the atom E. There are 16 pairs in the isoelectronic clusters (2 R2C2B4H4 fragments = 14 pairs + E = 2 pairs) and m + + o = 2 + 13- -l = 16. The need for parameter o is discussed in the Jemmis article in the reading list. 

Related work proved the presence and determined the source of the interstitial nitride in the isoelectronic cluster [Rh6N(CO)i5] , and the facile interconversion of the trigonal prismatic and octahedral clusters (Equation 3). ... 

The structures of [Mo(CO)4(AuPPh3)5]+ " and [Mo(CO)3(AuPPh3)7]+ are shown in Fig. 5. The structure of [Mo(CO)5(AuPPh3)3]+ was not determined. It can, however, be assumed that it has the same structure as the isoelectronic cluster V(CO)5(AuPPh3)3.f Flomonuclear gold cluster compounds are always formed as by-products, but the amount can be reduced by using an excess of the metal carbonyl complex. 

It is interesting to note that cluster stability is reduced if Au is substituted by Cu, forming the hypothetical isoelectronic cluster compound [(R3PCu)6C] +. Most... 

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