Chapter 10: Transition Metal Complexes and Coordination Compounds
Introduction
In this chapter, we explore the concept of coordination chemistry . Coordination complexes and complex ions are fascinating chemical species formed when a central transition metal atom or ion bonds to surrounding molecules or ions called ligands . These ligands act as Lewis Acids who donate electron pairs to the metal, creating a structure with unique geometric and electronic properties. The versatility of coordination complexes stems from their diverse bonding arrangements, variable oxidation states, and the ability of transition metals to accommodate different numbers of ligands.
These compounds are integral to many natural and technological processes. The vivid colors of many transition metal complexes also find use in pigments, dyes, and displays. Additionally, their ability to bind selectively to certain ions or molecules makes them valuable in analytical chemistry, medicine, and environmental remediation.
Figure 10.1: Glazed ceramic Sphinx of Amenhotep III, c. 1390-1352 B.C.E. The beautiful blue color of this glaze technique is due to copper-based coordination compounds that have structural properties allowing for the absorption, reflection, and emission of visible electromagnetic radiation (CC 1.0: Metroplitan Museum of Modern Art via WikiMedia Commons )
In biology, coordination complexes are essential for life; hemoglobin, for instance, uses an iron-centered complex to transport oxygen in the bloodstream. In industry, they are crucial for catalysis, such as in the production of plastics and pharmaceuticals. In modern materials science, coordination compounds are used in catalysts, dyes, and even medical imaging agents like MRI contrast media. Studying coordination complexes reveals the behaviors of the often-ignored transition metals, which opens doors to innovations in materials science, medicine, and technology.
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- 10.1: Properties of Transition Metals
- The transition metals are elements with partially filled d orbitals, located in the d-block of the periodic table. The reactivity of the transition elements varies widely from very active metals such as scandium and iron to almost inert elements, such as the platinum metals. The type of chemistry used in the isolation of the elements from their ores depends upon the concentration of the element in its ore and the difficulty of reducing ions of the elements to the metals.
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- 10.3: Ligands and Coordinate Bonds
- Crystal field theory treats interactions between the electrons on the metal and the ligands as a simple electrostatic effect. The presence of the ligands near the metal ion changes the energies of the metal d orbitals relative to their energies in the free ion. Both the color and the magnetic properties of a complex can be attributed to this crystal field splitting. The magnitude of the splitting depends on the nature of the ligands bonded to the metal.
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- 10.4: Molecular Geometry and Isomerization
- Two compounds that have the same formula and the same connectivity do not always have the same shape. There are two reasons why this may happen. In one case, the molecule may be flexible, so that it can twist into different shapes via rotation around individual sigma bonds. This phenomenon is called conformation, and it is covered in a different chapter. The second case occurs when two molecules appear to be connected the same way on paper, but are connected in two different ways in three dimens
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- 10.5: Metal Complexes in Living Organisms
- In this section, we describe several systems that illustrate the roles transition metals play in biological systems. Our goal is for you to understand why the chemical properties of these elements make them essential for life. We begin with a discussion of the strategies organisms use to extract transition metals from their environment.