Introduction to Coordination Chemistry

The Alsatian-Swiss chemist Alfred Werner pioneered the field of coordination chemistry in the late nineteenth century. At that time, a number of compounds of cobalt(III) chloride with ammonia were known. They had the following chemical 

Werner realized that he could test his hypothesis by measuring the electrical conductivity of aqueous solutions of the salts of these complex ions. Ions are the electrical conductors in aqueous solutions, and the conductivity is proportional to the ion concentration. If Werner s proposal was correct, then an aqueous solution of Compound 1, for example, should have a molar conductivity close to that of an aqueous solution of A1(N03)3, which also forms four ions per formula unit on complete dissociation in water (one 3+ ion and three 1— ions). His experiments confirmed that the conductivities of these two solutions were, indeed, similar. Furthermore the conductivity of aqueous solutions of compound 2 was close to those of Mg(N03)i, and solutions of compound 3 conducted electricity about as well as those containing NaN03. Compound 4, in contrast, did not dissociate into ions when dissolved in water, producing a solution of very low electrical conductivity. 

Werner and other chemists studied a variety of other coordination complexes, using both physical and chemical techniques. Their research has shown that the most common coordination number by far is 6, as in the cobalt complexes discussed earlier. Coordination numbers ranging from 1 to 16 are commonly observed, however. Examples include coordination numbers 2 (as in [Ag(NH2)2] ), 4 (as in [PtCU] ), and 5 (as in [Ni(CN)5] ). 

A second example illustrates the ability of transition metals to form complexes with small molecules and ions. Copper metal and hot concentrated sulfuric acid ( oil of vitriol ) react to form solid copper(II) sulfate, commonly called blue vitriol by virtue of its deep blue color. There is more to this compound than copper and sulfate, however it contains water as well. When the water is driven away by heating, the blue color vanishes, leaving greenish white anhydrous copper(II) sulfate (Fig. 8.11). The blue color of blue vitriol comes from a 

FIGURE 8.11 Hydrated copper(ll) sulfate, CuS04 5H20, is blue (left), but the anhydrous compound, CUSO4, is greenish white (right). A structural study of the solid compound demonstrates that four of the water molecules are closely associated with the copper and the fifth is not. Thus, a better representation of the hydrated compound is [Cu(H20)4]S04-H20. 

---

Porterfield, W. W. (1993). Inorganic Chemistry—A Unified Approach, 2nd ed. Academic Press, San Diego, CA. Chapters 10 through 12 give a good introduction to coordination chemistry. 

Graddon, D. P., An Introduction to Coordination Chemistry, Pergamon, London, 1961. 

Lawrance, G. (2010). Introduction to Coordination Chemistry. New York John Wiley. 

Introduction to Coordination Chemistry Geoffrey A. Lawrance 2010 John Wiley Sons, Ltd... 

---