1. Chapter 23 Transition Metals and Coordination Chemistry
Lecture Presentation
Chapter 23 Transition Metals and Coordination Chemistry
John D. Bookstaver
St. Charles Community College
Cottleville, MO
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Minerals
Most metals, including transition metals, are found in solid inorganic compounds known as minerals.
Minerals are named by common, not chemical, names.
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Atomic Radii
As one goes from left to right across a row, we see a decrease, then an increase in the radius of transition metals.
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Atomic Radii
On the one hand, increasing effective nuclear charge tends to make atoms smaller.
On the other hand, the strongest (and, therefore, shortest) metallic bonds are found in the center of the transition metals.
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5. Traits of Transition Metals
Because most transition metals have only partially occupied d subshells, the metals and/or their compounds often
Have more than one oxidation state.
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6. Traits of Transition Metals
Because most transition metals have only partially occupied d subshells, the metals and/or their compounds often
Have more than one oxidation state,
Are pigmented.
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7. Traits of Transition Metals
Because most transition metals have only partially occupied d subshells, the metals and/or their compounds often
Have more than one oxidation state,
Are pigmented,
Have magnetic properties.
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Paramagnetism
Paramagnetism, as you recall from Chapter 9, results from an atom having unpaired electrons.
Such atoms, then, show attraction to a magnet placed close by.
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Ferromagnetism
In ferromagnetic substances, the unpaired spins influence each other to align in the same direction, thereby exhibiting strong attractions to an external magnetic field.
Such species are permanent magnets.
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Antiferromagnetism
Antiferromagnetic substances have unpaired spins on adjacent atoms that align in opposing directions.
These magnetic fields tend to cancel each other.
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Ferrimagnetism
Ferrimagnetic substances have spins that align opposite each other, but the spins are not equal, so there is a net magnetic field.
Examples are NiMnO3, Y3Fe5O12, and Fe3O4.
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Complexes
Commonly, transition metals can have molecules or ions that covalently bond to them.
These give rise to complex ions or coordination compounds.
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Ligands
The molecules or ions that bind to the central metal are called ligands (from the Latin ligare, meaning “to bind”).
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Coordination
One of the properties that has led to the fascination with complexes and transition metals is the wide range of stunning colors found in them.
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Werner Theory
The Swiss chemist Alfred Werner deduced that there was a difference between the oxidation number of a metal and the number of ligands it took on, which he called the coordination number.
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Werner Theory
Thus, although the first two complexes in the table above each have 3 chlorines, in the first all three serve as anions, while in the second one of the chlorines is tightly bound to the cobalt and the other two are counterions.
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The Metal–Ligand Bond
The reaction between a metal and a ligand is a reaction between a Lewis acid (the metal) and Lewis base (the ligand).
The new complex has distinct physical and chemical properties.
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Coordination Numbers
The coordination number of a metal depends upon the size of the metal and the size of the ligands.
While iron(III) can bind to 6 fluorides, it can only accommodate 4 of the larger chlorides.
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19. Predicting Coordination number
Ag+: coordination number = 2 (2 ligand bonding positions); results in a linear complex
[Ag(NH3)2]+ (aq)
H H H | | |
Ag+ (aq) + 2 :N ─ H (aq) → H─ N:Ag:N─H (aq) | | |
H H H +

20. Zn2+ & Cu2+: coordination number = 4; tetrahedral complex
Ex: [Zn(H2O)4]2+ (aq)
Pt2+: coordination number = 4; square planar complex (d8 e- structure)
Ex: [Pt(CN)4]2- (aq)

21. Al3+, Cr3+, and Fe3+: coordination number = 6; octahedral complex
Ex: [Cr(NH3)5Cl]2+ (aq)

22. Is dependent on:
Charge of ligand:
Ni2+: 6 NH3 or 4 CN- (since CN- transfers more negative charge)
Size of ligand:
Fe3+: 6 F- or 4 Cl- (larger ions take up more space)

23. Predicting geometry Coordination number = 6
Nearly all are octahedral
Coordination number = 4 (if you don’t know, pick 4)
Most are tetrahedral
Metals ions with a d8 configuration are square planar (Pd2+, Pt2+, Ir+, Au3+)

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Common Ligands
The table above contains some ligands commonly found in complexes.
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Common Ligands
Monodentate ligands coordinate to one site on the metal, bidentate to two, and so forth.
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Common Ligands
Bi and polydentate ligands are also called chelating agents.
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27. Chelates in Biological Systems
There are many transition metals that are vital to human life.
Several of these are bound to chelating agents.
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28. Chelates in Biological Systems
For instance, the iron in hemoglobin carries O2 and CO2 through the blood.
Carbon monoxide and cyanide are poisonous because they will bind more tightly to the iron than will oxygen.
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29. Nomenclature in Coordination Chemistry
In naming complexes that are salts, the name of the cation is given before the name of the anion.
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30. Nomenclature in Coordination Chemistry
In naming complex ions or molecules, the ligands are named before the metal. Ligands are listed in alphabetical order, regardless of their charges.
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31. Nomenclature in Coordination Chemistry
The names of anionic ligands end in the letter o, but electrically neutral ligands ordinarily bear the name of the molecules.
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32. Nomenclature in Coordination Chemistry
Greek prefixes (di-, tri-, tetra-, etc.) are used to indicate the number of each kind of ligand when more than one is present. If the ligand contains a Greek prefix or is polydentate, the prefixes bis-, tris-, tetrakis-, etc. are used and the ligand name is placed in parentheses.
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33. Nomenclature in Coordination Chemistry
If the complex is an anion, its name ends in -ate.
The oxidation number of the metal is given in parentheses in Roman numerals following the name of the metal.
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Isomers
Isomers have the same molecular formula but a different arrangement of atoms.
There are two main subgroupings: structural isomers and stereoisomers.
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Linkage Isomers
In linkage isomers the ligand is bound to the metal by a different atom.
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38. Coordination Sphere Isomers
Coordination sphere isomers differ in what ligands are bound to the metal and which fall outside the coordination sphere.
For example, CrCl3(H2O)6 exists as
[Cr(H2O)6]Cl3,
[Cr(H2O)5Cl]Cl2H2O, or
[Cr(H2O)4Cl2]Cl2H2O.
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Geometric Isomers
In geometric isomers, the ligands have a different spatial relationship.
In the complexes above, the chlorines can be adjacent to each other (cis) or opposite each other (trans).
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Optical Isomers
Optical isomers, or enantiomers, are non-superimposable mirror images of one another.
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Color
The complex [Ti(H2O)6]3+ at the left appears red-violet because those are the wavelengths of visible light not absorbed by the complex.
Many complexes are pigmented because they absorb in the visible part of the spectrum.
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Crystal-Field Theory
As was mentioned earlier, ligands are Lewis bases that are attracted to a Lewis acid (the metal).
But d electrons on the metal would repel the ligand.
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Crystal-Field Theory
Therefore, the d orbitals on a metal in a complex would not be degenerate.
Those that point toward ligands would be higher in energy than those that do not.
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Crystal-Field Theory
The energy gap between d orbitals often corresponds to the energy in a photon of visible light.
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Crystal-Field Theory
The spectrochemical series ranks ligands in order of their ability to increase the energy gap between d orbitals. (Increases with size and charge.)
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Crystal-Field Theory
The stronger the crystal-field strength of the ligand, the larger the energy gap between d orbitals, and the shorter the wavelength of light absorbed by the complex.
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