chapter 24 - Chapter 24 Chemistry of Coordination Compounds...

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Chapter 24 Chemistry of Coordination Compounds
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Compounds of transition metals consitute an important group of c o l o r e d substances. Use in making paint pigments, colors in glass, fireworks, precious gems.
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Complexes A central metal atom bonded to a group of molecules or ions is a metal complex . If the complex bears a charge, it is a complex ion . Compounds containing complexes are coordination compounds .
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Complexes The molecules or ions coordinating to the metal are the ligands . They are usually anions or polar molecules.
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Coordination Compounds Many coordination compounds are brightly colored. Properties of Some Ammonia Complexes of Cobalt (III)
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Coordination Compounds Many coordination compounds are brightly colored. Properties of Some Ammonia Complexes of Cobalt (III)
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Coordination Compounds Different coordination compounds from the same metal and ligands can give quite different numbers of ions when they dissolve.
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Werner’s Theory Alfred Werner suggested in 1893 that metal ions exhibit what he called primary and secondary valences. Primary valences are the oxidation number for the metal (+3 on the cobalt at the right). Secondary valences are the coordination number, the number of atoms directly bonded to the metal (6 in the complex at the right).
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Werner’s Theory The central metal and the ligands directly bonded to it make up the coordination sphere of the complex. • In CoCl 3 6 NH 3 , all six of the ligands are NH 3 and the 3 chloride ions are outside the coordination sphere.
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Werner’s Theory In CoCl 3 5 NH 3 the five NH 3 groups and one chlorine are bonded to the cobalt, and the other two chloride ions are outside the sphere.
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Werner’s Theory Werner proposed putting all molecules and ions within the sphere in brackets and those “free” anions (that dissociate from the complex ion when dissolved in water) outside the brackets.
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Werner’s Theory This approach correctly predicts there would be two forms of CoCl 3 4 NH 3 . The formula would be written 3 4 2
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The Development of Coordination Chemistry: Werner’s Theory Metal Complexes Metal Complexes
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The Metal-Ligand Bond All ligands (Lewis bases) have lone pairs that are donated to the metal ion (Lewis base). The bond between metal and ligand is a 2-electron bond, but both electrons come from the ligand and none from the metal. Metal Complexes Metal Complexes
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Metal-Ligand Bond The coordination of the ligand with the metal can greatly alter its physical properties, such as color, or chemical properties, such as ease of oxidation (see next slide).
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The Metal-Ligand Bond The metal-ligand bond alters the physical properties of the metal: Metal Complexes Metal Complexes
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This bond is formed between a Lewis acid and a Lewis base. The ligands (Lewis bases) have nonbonding
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chapter 24 - Chapter 24 Chemistry of Coordination Compounds...

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