1. Sections 2-4 Transition Metal Complexes
Chapter 23
Sections 2-4 Transition Metal Complexes
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2. © 2012 Pearson Education, Inc.
Complexes
Commonly, transition metals can have molecules or ions that 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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4. Yes. Ammonia is the Lewis acid.
Yes. The metal cation is the Lewis acid.
No. Ammonia is a neutral molecule and cannot can not accept electron density from a Lewis base.
No. The metal cation cannot accept electron density from a Lewis base.
Answer: B

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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.
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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7. Sample Exercise 23.1 Identifying the Coordination Sphere of a Complex
Palladium(II) tends to form complexes with coordination number 4. A compound has the composition PdCl2 · 3 NH3. (a) Write the formula for this compound that best shows the coordination structure. (b) When an aqueous solution of the compound is treated with excess AgNO3(aq), how many moles of AgCl(s) are formed per mole of PdCl2 · 3 NH3?
Solution
Practice Exercise
Predict the number of ions produced per formula unit in an aqueous solution of CoCl2 · 6 H2O. 7

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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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9. A. [Fe(H2O)4]3+(aq) + SCN–(aq)  [Fe(H2O)3NCS]2+(aq) + H2O(l)
Answer: D
A. [Fe(H2O)4]3+(aq) + SCN–(aq)  [Fe(H2O)3NCS]2+(aq) + H2O(l)
B. [Fe(H2O)4]3+(aq) + S2+(aq) + CN–(aq)  [Fe(H2O)5NCS]2+(aq) + H2O(l)
C. Fe3+(aq) + 3SCN–(aq)  FeCN3 (aq) + 3S–(aq)
D. [Fe(H2O)6]3+ (aq) + SCN–(aq)  [Fe(H2O)5NCS]2+(aq) + H2O(l)

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Coordination Numbers
The number of atoms directly bonded to the metal atom in a complex is the coordination number.
Compound
Coordination number
[Ag(NH3)2]+ 2
[Co(NH3)6]Cl3 6
[Co(NH3)5Cl]Cl2
trans -[Co(NH3)4Cl2]Cl
cis -[Co(NH3)5Cl2]Cl
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11. Solution Practice Exercise
Sample Exercise 23.2 Determining the Oxidation Number of a Metal in a Complex
What is the oxidation number of the metal in [Rh(NH3)5Cl](NO3)2?
Solution
Practice Exercise
What is the charge of the complex formed by a platinum(II) metal ion surrounded by two ammonia molecules and two bromide ions? 11

12. Solution Practice Exercise
Sample Exercise 23.3 Determining the Formula of a Complex Ion
A complex ion contains a chromium(III) bound to four water molecules and to two chloride ions.What is the formula and charge of this ion?
Solution
Practice Exercise
Write the formula for the complex described in the Practice Exercise accompanying Sample Exercise 23.2. 12

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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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14. NH3—Zn—NH3 NH3—Pt—NH3 A. 109.5° 90° B. 120° 109.5° C. 180° 120°
Answer: A
NH3—Zn—NH3 NH3—Pt—NH3
A ° 90°
B. 120° °
C. 180° 120°
D. 120° 90°

15. Octahedral Tetrahedral Tetrahedral Octahedral Octahedral Square planar
Geometries: C.N. = 4 C.N. = 6
Octahedral Tetrahedral
Tetrahedral Octahedral
Octahedral Square planar
Square planar Tetrahedral
Answer: B

16. A. Two for both B. Three for both C. Four for both D. Six for both
Answer: C

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Common Ligands
The table above contains some ligands commonly found in complexes.
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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19. Bidentate ligand
Monodentate ligand
Answer: A

20. 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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21. Chelates in Biological Systems
For instance, the iron in hemoglobin carries O2 and CO2 through the blood.
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22. A. On the protein group B. On the heme group C. On the NH group
D. Where O2 binds
Answer: D

23. 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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24. A. 420 nm
B nm
C nm
D nm
Answer: D

25. The C-C bonds absorb light in the ultraviolet region.
It has a planar structure that enables the C-H bonds to absorb light in the visible region.
The C-C bonds absorb light in the ultraviolet region.
It has conjugated double bonds that absorb light in the visible region.
It has C-H bonds that absorb light in the infrared region.
Answer: C

26. 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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27. 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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28. 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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29. 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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30. 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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31. Solution Practice Exercise
Sample Exercise 23.4 Naming Coordination Compounds
Name the compounds (a) [Cr(H2O)4Cl2]Cl, (b) K4[Ni(CN)4].
Solution
Practice Exercise
Name the compounds (a) [Mo(NH3)3Br3]NO3, (b) (NH4)2[CuBr4]. (c) Write the formula for sodium diaquabis(oxalato)ruthenate(III). 31