Main group-transition metal cluster characterization

Heating peralkylated derivatives 56a in BBr3 leads selectively to the 6-bromo derivatives 56b via Br/alkyl exchange [74], Among other transformations, the reaction of 56b with the sodium salt of a thioazadiiron cluster is an example of combining main group and transition metal clusters in one molecule (56c), which provided crystals for structural characterization (Scheme 3.2-29) [75]. 

Since the initial structural determination of [Fe5C(CO)i5] by Dahl in which demonstrated the possibility of forming transition metal clusters incorporating main-group interstitial atoms, many examples have been characterized. 

Ni8( U4-PPh)6(CO)8 (1), characterized by Lower and Dahl 20 years ago " is a typical representative example of an empty cubic inorganic transition-metal cluster of formula M8(/i4-E)6Lx (M = transition metal, E = main group element or ligand, L = two-electron terminal ligand (CO, PR3, Cl ...) and x <8). 

The term Zintl phase is applied to solids formed between either an alkali- or alkaline-earth metal and a main group p-block element from group 14, 15, or 16 in the periodic table. These phases are characterized by a network of homonuclear or heteronuclear polyatomic clusters (the Zintl ions), which carry a net negative charge, and that are neutralized by cations. Broader definitions of the Zintl phase are sometimes used. Group 13 elements have been included with the Zintl anions and an electropositive rare-earth element or transition element with a filled d shell (e.g. Cu) or empty d shell (e.g. Ti) has replaced the alkali- or alkaline-earth element in some reports. Although the bonding between the Zintl ions and the cations in the Zintl phases is markedly polar, by our earlier definition those compounds formed between the alkali- or alkaline-earth metals with the heavier anions (i.e. Sn, Pb, Bi) can be considered intermetallic phases. 

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