This has many potential useful applications, from powering cars with hydrogen fuel cells to making better electronics components.
Although not a complex, self-darkening sunglasses are an example of a photoactive substance. Watch this video to learn more about this research and listen to Dr.
Many other coordination complexes are also brightly colored. The square planar copper II complex phthalocyanine blue from Figure 14 is one of many complexes used as pigments or dyes. This complex is used in blue ink, blue jeans, and certain blue paints. The structure of heme Figure 18 , the iron-containing complex in hemoglobin, is very similar to that in chlorophyll.
In hemoglobin, the red heme complex is bonded to a large protein molecule globin by the attachment of the protein to the heme ligand. Oxygen molecules are transported by hemoglobin in the blood by being bound to the iron center. When the hemoglobin loses its oxygen, the color changes to a bluish red.
Many metal ions are also undesirable in food products because these ions can catalyze reactions that change the color of food. Coordination complexes are useful as preservatives. This ligand also is used to sequester metal ions in paper production, textiles, and detergents, and has pharmaceutical uses. Complexing agents that tie up metal ions are also used as drugs. BAL is now used to treat poisoning by heavy metals, such as arsenic, mercury, thallium, and chromium.
The drug is a ligand and functions by making a water-soluble chelate of the metal; the kidneys eliminate this metal chelate Figure As the transfused blood breaks down, the usual metabolic processes that remove iron are overloaded, and excess iron can build up to fatal levels.
Enterobactin forms a water-soluble complex with excess iron, and the body can safely eliminate this complex. Chelation Therapy Ligands like BAL and enterobactin are important in medical treatments for heavy metal poisoning. However, chelation therapies can disrupt the normal concentration of ions in the body, leading to serious side effects, so researchers are searching for new chelation drugs.
Identify which atoms in this molecule could act as donor atoms. Solution All of the oxygen and sulfur atoms have lone pairs of electrons that can be used to coordinate to a metal center, so there are six possible donor atoms.
Geometrically, only two of these atoms can be coordinated to a metal at once. The most common binding mode involves the coordination of one sulfur atom and one oxygen atom, forming a five-member ring with the metal. Check Your Learning Some alternative medicine practitioners recommend chelation treatments for ailments that are not clearly related to heavy metals, such as cancer and autism, although the practice is discouraged by many scientific organizations.
Ligands are also used in the electroplating industry. When metal ions are reduced to produce thin metal coatings, metals can clump together to form clusters and nanoparticles. When metal coordination complexes are used, the ligands keep the metal atoms isolated from each other. It has been found that many metals plate out as a smoother, more uniform, better-looking, and more adherent surface when plated from a bath containing the metal as a complex ion.
In , scientists at Michigan State University discovered that there was a platinum complex that inhibited cell division in certain microorganisms.
Later work showed that the complex was cis -diaminedichloroplatinum II , [Pt NH 3 2 Cl 2 ], and that the trans isomer was not effective. The inhibition of cell division indicated that this square planar compound could be an anticancer agent. In , the US Food and Drug Administration approved this compound, known as cisplatin, for use in the treatment of certain forms of cancer. Since that time, many similar platinum compounds have been developed for the treatment of cancer.
In all cases, these are the cis isomers and never the trans isomers. The diamine NH 3 2 portion is retained with other groups, replacing the dichloro [ Cl 2 ] portion. The newer drugs include carboplatin, oxaliplatin, and satraplatin. The transition elements and main group elements can form coordination compounds, or complexes, in which a central metal atom or ion is bonded to one or more ligands by coordinate covalent bonds. Ligands with more than one donor atom are called polydentate ligands and form chelates.
The common geometries found in complexes are tetrahedral and square planar both with a coordination number of four and octahedral with a coordination number of six. Cis and trans configurations are possible in some octahedral and square planar complexes.
In addition to these geometrical isomers, optical isomers molecules or ions that are mirror images but not superimposable are possible in certain octahedral complexes. Coordination complexes have a wide variety of uses including oxygen transport in blood, water purification, and pharmaceutical use. When they are cis , there will also be an optical isomer. Skip to content Chapter Transition Metals and Coordination Chemistry.
Learning Objectives By the end of this section, you will be able to: List the defining traits of coordination compounds Describe the structures of complexes containing monodentate and polydentate ligands Use standard nomenclature rules to name coordination compounds Explain and provide examples of geometric and optical isomerism Identify several natural and technological occurrences of coordination compounds.
Example 1 Coordination Numbers and Oxidation States Determine the name of the following complexes and give the coordination number of the central metal atom. Answer: K[Ag CN 2 ]; coordination number two. Figure The trans isomer of [Pt NH 3 2 Cl 2 ] has each ligand directly across from an adjacent ligand.
Transition Metal Catalysts One of the most important applications of transition metals is as industrial catalysts. Like the square planar platinum complexes seen before, these compounds consist of metal ions with other atoms or groups bound to them. More information about the binding of ligands to metals is found in the section on Lewis acids and bases.
These groups that bind to metal ions are called ligands. One example of a type of octahedral compounds that can form enantiomers is bidentate complexes. In bidentate complexes from the Greek two teeth or chelating complexes from the Greek crab , a ligand binds very tightly to the metal because it holds onto the metal via more than one atom.
Ethylenediamine is one example of a bidentate ligand. The spatial relationship between the metal and the two atoms connected to it from the same ligand forms a plane.
If more than one bidentate ligand is connected to the metal, the relative orientation of one plane to another creates the possibility of mirror images. A complex containing three bidentate ligands can take on the shape of a left-handed propeller or a right-handed propeller. If you turned this propellor, in what direction would the air be pushed? The shape shown applies to any ion of this kind. If your visual imagination will cope, you may be able to see that this ion has no plane of symmetry.
If you find this difficult to visualise, the only solution is to make the ion out of a lump of plasticene or a bit of clay or dough and three bits of cardboard cut to shape. A substance with no plane of symmetry is going to have optical isomers - one of which is the mirror image of the other. One of the isomers will rotate the plane of polarisation of plane polarised light clockwise; the other rotates it anti-clockwise.
If you don't understand what I am talking about, it is because you didn't take my advice and follow the link to the isomerism part of the site earlier on this page! You need to read about optical isomerism in the organic chemistry section of this site. If you have a really impressive visual imagination, you may be able to see that there is no way of rotating the second isomer in space so that it looks exactly the same as the first one. I can't do this! The only way I have ever been able to convince myself that they are different is to make models.
For exam purposes, this doesn't matter in the slightest. As long as you draw the isomers carefully, with the second one a true reflection of the first, the two structures will be different. If this is the first set of questions you have done, please read the introductory page before you start. Some simple shapes for complex ions These shapes are for complex ions formed using monodentate ligands - ligands which only form one bond to the central metal ion. The diagram shows four fairly random examples of octahedral ions.
Tetrahedral ions These are the ones you are most likely to need for A' level purposes in the UK. That's not very difficult to remember either! A square planar complex Occasionally a 4-co-ordinated complex turns out to be square planar. Stereoisomerism in complex ions Some complex ions can show either optical or geometric isomerism. There are two completely different ways in which the ammonias and chloride ions could arrange themselves around the central platinum ion: The two structures drawn are isomers because there is no way that you can just twist one to turn it into the other.
Optical isomerism You recognise optical isomers because they have no plane of symmetry. Use the BACK button on your browser to return to this page. In this case, the two isomers are: If you have a really impressive visual imagination, you may be able to see that there is no way of rotating the second isomer in space so that it looks exactly the same as the first one.
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