Higher coordination numbers of metals in finite complexes

Higher coordination numbers of metals in finite complexes 

We have collected together in this section some examples of finite complexes formed with polydentate ligands in which transition metals exhibit coordination numbers from 7 to 10. For chelates of 4f metals see p. 67. 

We noted in Chapter 10 two rather symmetrical arrangements of 7 nearest neighbours found in oxy- and fluoro-compounds of transition metals, namely, pentagonal bipyramidal (ZrF ), and monocapped trigonal prism (NbF ). The ions formed from ethylenediamine tetracetic acid and the closely related diamino cyclohexane acid are potentially sexadentate ligands, for there are 4 0 atoms and 

2 N atoms which can coordinate to a metal atom. In the formulae in this section and in Fig. 27.3 we use the abbreviations edta and dcta to mean the ions (4 -) 

It is evident that the geometries of these 7-coordinated complexes are very much dependent on the constraints due to the shapes of the polydentate ligands. A more extreme example is the pentagonal bipyramidal coordination in complexes formed by the pentadentate ligand L, such as the cations in the salts [FeL(NCS)2]C104, (where the NCS groups occupy the apical positions with Fe—N, 2-01 A as compared 

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