Coordination Chemistry Complexes

Overview

Source: Laboratory of Dr. Neal Abrams — SUNY College of Environmental Science and Forestry

Transition metals are found everywhere from vitamin supplements to electroplating baths. Transition metals also make up the pigments in many paints and compose all minerals. Typically, transition metals are found in the cationic form since they readily oxidize, or lose electrons, and are surrounded by electron donors called ligands. These ligands do not form ionic or covalent bonds with the metal center, rather they take on a third type of bond known as coordinate-covalent. The coordinate-covalent bond between a ligand and a metal is dynamic, meaning that ligands are continuously exchanging and re-coordinating around the metal center. The identities of both the metal and the ligand dictates which ligands will bond preferentially over another. In addition, color and magnetic properties are also due to the types of complexes that are formed. The coordination compounds that form are analyzed using a variety of instruments and tools. This experiment explores why so many complexes are possible and uses a spectrochemical (color and chemical) method to help identify the type of coordination complex that forms.

Procedure

1. Nickel Complexes and Colors

Ni(H₂O)₆²⁺ complex (Figure 1a)
1. Prepare a 1 M solution of Ni(H₂O)₆²⁺ by dissolving NiSO₄ in the appropriate volume of water.
2. Further dilute the Ni(H₂O)₆²⁺solution by adding 70 mL of the 1 M solution to 1,000 mL of deionized water.
3. Divide the Ni(H₂O)₆²⁺ among seven 400-mL beakers.

Application and Summary

From pigments to people, transitional metals are found throughout fields of chemistry, biology, geology, and engineering. Understanding the behavior of transition metals under different chemical states can be as simple as monitoring color or magnetic behavior. Nearly every 3d (4^th row) transition metal is vital to physiological function and, in all cases, these metals are bound by ligands to form coordination complexes. For example, iron is vital to oxygen transport in all vertebrates. Hemoglobin, a complex pr

References

Shakhashiri, B. Z.; G. E. Dirreen, G. E; Juergens, F. Color, Solubility, and Complex Ion Equilibria of Nickel (II) Species in Aqueous Solution. J. Chem. Ed. 52 (12), 900-901 (1980).

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