ABSTRACT
However, there are many other types of compounds often referred to as clusters (see Figure 1.1). For example, there are many types of single element main group clusters such as P4 (white phosphorus), Ss and fullerenes (e.g C60) as well as zintl ions, e.g. TI99-and TI1311-, that are formed by the late transition and post transition metals. Clusters that are composed of only skeletal atoms, i.e. with no other ligands or groups attached, like the main group compounds mentioned above, are compara tively rare. Most cluster skeletons are surrounded, at least to some extent, by a shell of ligands. This book deals with transition metal clusters that are prim arily decorated with carbonyl ligands. However, other types of clusters are stabilised by different ligands including borane (hydroboron) clusters that from an historical perspective laid the foundations of cluster science, and Fe4S4 based clusters ubiquitous in biological electron transfer processes. Other examples o f much larger main grouptransition metal clusters include compounds such as [CdioS4Br4(SC6H4M e-l,4)i2]4_,
Cu72Se36(PPh3)20, C u i46Se73(PPh3)3o and Ag3oTe9(TePh)i2(PEt3)i2. The compounds described above are defined as clusters as they have three-
dimensional shapes and there are direct element-element bonds between the skeletal atoms. There are many more examples o f cage compounds where three-dimensional
structures are formed without direct element-element bonds between the same element, and are therefore beyond the scope of this introduction.
