Coordination Chemistry1

Coordination Chemistry1 - Coordination Chemistry1 Authors D...

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Coordination Chemistry 1 Authors: D. Afzal, H. D. Ervin, A. E. Moody, H. D. Wohlers, and J. M. McCormick* Last Update: December 29, 2006 Introduction In this experiment you will be synthesizing three coordination compounds and analyzing them. Coordination compounds (also known as complex ions and complexes) are formed by the reaction of a Lewis acid (usually a transition metal) with a Lewis base, which is known as a ligand. What is unique about coordination compounds is that they are formed from chemical species that have an independent existence and that this association is often readily reversible (i. e., there is an equilibrium between the solvated metal ion and the ligand). For example, NiCl 2 reacts with NH 3 in aqueous solution to form the compound Ni(NH 3 ) 6 Cl 2 which contains the complex ion [Ni(NH 3 ) 6 ] 2+ . This process is easily reversed (by the addition of H + ) to give back the starting materials. This type of behavior was thought to be very peculiar by chemists in the 1800's. They were familiar with compounds like CO 2 , which although it could be made from C and O 2 , does not act like it is some loose association of C and O 2 . It wasn’t until the ground- breaking work of Werner (for which he won the Nobel Prize in chemistry) in the late 19 th and early 20 th centuries that chemists began to understand these compounds. Werner’s work was greatly expanded on in the 20 th century especially after it was discovered that coordination chemistry was relevant to the understanding the role of metal ions in biological systems. You will be preparing complexes of Co 3+ with ethylenediamine, NH 2 CH 2 CH 2 NH 2 (abbreviated: en ), and of Fe 3+ with the oxalate ion, C 2 O 4 2- (abbreviated: ox ). Ethylenediamine and oxalate are examples of bidentate ligands, which means that they have two different atoms that can donate electron pairs to a metal ion. Ethylenediamine does this through its nitrogen atoms, while oxalate donates electron pairs from two of its four oxygens. In all of these complexes the metal ion is directly bonded to six other atoms in what is called an octahedral geometry (if we connected the six atoms, the resulting solid would be an octahedron, and hence the name of this geometry). Although it may not be obvious, there may be many ways in which the same six atoms can be arranged around a central atom in an octahedral geometry, and each of these different arrangements may give rise to compounds with the same chemical formula, but have different arrangements of their atoms ( isomers ). There are many types of isomers: compounds in which the actual connections between atoms (bonds) are different are called constitutional isomers , while compounds where the bonds are the same, but the atoms are arranged differently are called geometric isomers . Geometric isomers are further classified as enantiomers (two compounds that are mirror images of each other) and diastereomers (geometric isomers that are not mirror images).
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This lab report was uploaded on 04/17/2008 for the course CHEM 121 taught by Professor Baughman during the Spring '08 term at Truman State.

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Coordination Chemistry1 - Coordination Chemistry1 Authors D...

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