Geometry of complex ions

The physical and chemical properties of complex ions and of the coordination compounds they form depend on the spatial orientation of ligands around the central metal atom. Here we consider the geometries associated with the coordination numbers 2,4, and 6. With that background, we then examine the phenomenon of geometric isomerism, in which two or more complex ions have the same chemical formula but different properties because of their different geometries. 

Complex ions in which the central metal forms only two bonds to ligands are linear that is, the two bonds are directed at a 180° angle. The structures of CuCl2, Ag(NH3)2+, and Au(CN)2 may be represented as 

Square planar complexes, in which the four bonds are directed toward the comers of a square, are more common. Certain complexes of copper(II) and nickel(II) show this geometry it is characteristic of die complexes of Pd2+ and Pt2+, including Pt(NH3)42+. 

Click Coached Problems for a self-study module on the geometry of transition metal complexes. 

We saw in Chapter 7 that octahedral geometry is characteristic of many molecules (e.g., SF6) in which a central atom is surrounded by six other atoms. (Remember, an octahedron has eight sides, which is irrelevant here it has six comers, which is important) All complex ions 

Two or more species with different physical and chemical properties but the same formula are said to be isomers of one another. Complexions can show many different kinds of isomerism, only one of which we will consider. Geometric isomers are ones that differ only in the spatial orientation of ligands around the central metal atom. Geometric isomerism is found in square planar and octahedral complexes. It cannot occur in tetrahedral complexes where all four positions are equivalent. 

Square planar. There are two compounds with the formula Pt(NH3)2Cl2, differing in water solubility, melting point, chemical behavior, and biological activity. Their structures are 

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The basic ideas concerning the structure and geometry of complex ions presented in this chapter were developed by one of the most gifted individuals in the history of inorganic chemistry,... 

FIGURE 22.9 Common geometries of complex ions. In each case M is a metal and L is a monodentate ligand. 

Although we described the formation of a complex as a Lewis acid—base reaction (Section 23.3), we did not go into any details of structure. We did not look at the geometry of complex ions or inquire about the precise nature of the bonding. Three properties of complexes have proved pivotal in determining these details. 

The common geometries of complex ions, shown in Table 24.3, depend in part on their coordination number. A coordination number of 2 results in a linear geometry, and a coordination number of 6 results in an octahedral geometry. A coordination number of 4... 

TABLE 19.2 Coordination Number and Geometry of Complex Ions ... 

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