1	Chapter 24 Chemistry of Coordination Compounds
2	Complexes of Co³⁺
3	Coordination Compounds A metal cation is capable of forming two types of bonds: An ionic bond which is the attraction between oppositely charged ions. Was originally called a primary valence. Ionic bonds come apart in water solution. A covalent bond between the metal cation and a small molecule or anion with a lone pair called a ligand. Was originally called a secondary valence. Shared pair of electrons originates from a lone pair on the ligand. Covalent bonds do not come apart in water.
4	Typical ligands
5	Back to Co³⁺ complexes CoCl₃·6NH₃ Co³⁺ ion forms 6 covalent bonds, one to each NH₃. The resulting polyatomic ion stays intact upon dissolving in water. It also has a +3 charge which is neutralized via ionic bonds with 3 Cl¯ ions. [Co(NH₃)₆]Cl₃ ¾® Co(NH₃)₆³⁺(aq) + 3 Cl¯(aq)
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7	Co³⁺ complexes CoCl₃·5NH₃ 6 ligands still attach to the Co³⁺ ions, 5 NH₃ molecules and 1 Cl¯ ion. Charge on the polyatomic ion is now +2. 2 Cl¯ ions are needed to complete the formula [Co(NH₃)₅Cl]Cl₂¾® Co(NH₃)₅Cl²⁺(aq) + 2 Cl¯(aq)
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9	Co³⁺ complexes CoCl₃·4NH₃ two complexes Co³⁺ forms covalent bonds to 6 ligands, 4 NH₃molecules and 2 Cl¯ anions. Charge on the polyatomic ion is now +1 It will have 1 Cl¯ ion to neutralize the charge There are two ways to place 2 Cl¯ ions in this arrangement, either next to each other (cis isomer) or opposite each other (trans isomer) [Co(NH₃)₄Cl₂]Cl ¾® Co(NH₃)₄Cl₂⁺(aq) + 2 Cl¯(aq)
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11	Coordination compounds Many metal cations form coordination compounds with a variety of ligands. Number of ligands that attach to a particular metal cation is called the coordination number for the metal cation. Coordination numbers range from 2 up to 6. Most common coordination numbers are 4 and 6.
12	Coordination compounds Charge on the complex Equal to the sum of the charge on the metal cation plus the charges on the ligands (if any).
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14	Typical geometries Coordination number 4 Two typical geometries: square planar or tetrahedral.
15	Typical geometries Coordination number 6: octahedral
16	Ligands having more than one pair of electrons to donate. Some ligands can bind to a metal cation from more than one site in the ligand. These ligands are called polydentate ligands. They are also called chelating agents.
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18	Chelates in living systems Many important enzymes: chlorophyll, myoglobin and hemoglobin contain a porphyrin ring.
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22	Isomerism in Coordination Complexes Structural isomers (different linkages) Coordination sphere [Cr(H₂O)₆]Cl₃ versus [Cr(H₂O)₅Cl]Cl₂·H₂O Linkage isomerism A ligand can bind by more than one end.
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24	Geometric isomerism Can have cis-, trans- isomerism in coordination complexes
25	Optical Isomers
26	Colors of coordination complexes Many transition metal complexes change their color when different ligands attach to it. When a compound is colored that means that the compound absorbs a particular frequency of light in the visible region of the electromagnetic spectrum The compound absorbs the complement of the color observed.
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28	Why are coordination complexes colored? When the ligands attach, the energies of the d orbitals on the metal split in energy.
29	Colors!! The size of the split corresponds to photon energies in the visible region. The size of the split will depend on what ligands are attached. Crystal Field Theory.