24.1+Metal+Complexes

Vocabulary:
A **coordination compound** is a compound containing a metal ion bonded to a group of surrounding molecules or ions that act as ligands.Other names for this term are: complex ion, metal complex and coordination complex.

A **ligand** is the molecule or ion that bond to the metal ion in a complex. In general each ligand functions as a Lewis base (donates a pair of electrons) to form a bond with the metal. Every ligand must have one unshared pair of valence electrons.

This term was originally defined by **Alfred Werner**.
 * Coordination number** refers to the total number of neighbors that the central atom has.


 * Coordination Sphere** refers to the central atom and the arrangement of anions around it.


 * Donor Atom** is the atom of the ligand bound to the metal directly.

[[image:Alfred-Werner[1].jpg align="right"]]The Development of Coordination Chemistry: Werner's Theory
In 1893, the Swiss chemist **Alfred Werner** had a break through on why different transition metals exhibited many colors, his theory would become known as Werner's Theory. This theory states that metal ions have both a __primary__ and __secondary__ valences. He concluded that the primary valence held the key to the oxidation state of the metal, while the secondary valence (coordination number) is the number of atoms directly bonded to the metal ion. With this theory the colors of transition metals could be explained. This theory also allowed for understandin the difference between coordinated and ionic in a compound. Werner won t he 1913 Noble Prize in Chemistry for this discovery.

Writing the Chemical Formula for a Coordination Compound:
1. Identify the central metal ion and its charge. 2. Identify the ligands, their number and charge. 3. Calculate the total charge of the complex (charge on metal ion + total charge on ligands) 4. Write the formula by naming the central metal ion first followed by the ligands. 5. Use square brackets to set off the coordination sphere from the other parts of the compound.

The Metal- Ligand Bond:
The bond between a metal and ligand is due to the interaction of a **Lewis base and a Lewis acid**. Ligands functions as __L. Bases since they have__ __sets of unshared pairs of electrons__. From these type of bond, chemical and physical properties of metal ion are formed; it can also change the ion's ability to be oxidized or reduced with ease.



Coordination Number

 * 1+ ions: 2 or 4. SPECIAL NOTE Ag is __always__ 2 [[image:shapes[1].png width="469" height="154" align="right"]]
 * 2+ ions: 4 or 6 PLEASE NOTE Fe is __always__ 6
 * 3+ ions: 6 ANOTHER NOTE Au is __always__ 4

Geometry: based on coordination number
 * 2= linear
 * 4= tetrahedral/ square pyramidal
 * 6=octohedral

[|Ligands and Complex Ions]
===[|Complex Ions]=== [|Suprise]


 * 1) Brown, Theodore L., and H. Eugene LeMay. Chemistry: The Central Science. Upper Saddle River, NJ: Pearson Prentice Hall, 2008. Print.
 * 2) "Chemistry Tutorial : Ligands and Complex Ions." //AUS-e-TUTE for Astute Science Students//. Web. 24 Mar. 2011. .
 * 3) "Introducing Complex Ions - Ligands and Bonding." //Chemguide: Helping You to Understand Chemistry - Main Menu//. Web. 24 Mar. 2011. [].
 * 4) Wight, Chuck. "YouTube - Transition Metal Complexes." //YouTube - Broadcast Yourself.// Web. 24 Mar. 2011. .