Plastics are made with the aid of transition metal catalysts, along with detergents, fertilizers, paints, and more see Figure Very complicated pharmaceuticals are manufactured with catalysts that are selective, reacting with one specific bond out of a large number of possibilities.
Catalysts allow processes to be more economical and more environmentally friendly. Developing new catalysts and better understanding of existing systems are important areas of current research. Her research combines the fields of fundamental inorganic and physical chemistry with materials engineering. She is working on many different projects that rely on transition metals.
For example, one type of compound she is developing captures carbon dioxide waste from power plants and catalytically converts it into useful products see Figure 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 This example is chosen because it is very similar to the last one - except that it involves a transition metal. Now, be careful!
The single electrons in the 3d level are NOT involved in the bonding in any way. Instead, the ion uses 6 orbitals from the 4s, 4p and 4d levels to accept lone pairs from the water molecules. Before they are used, the orbitals are re-organised hybridised to produce 6 orbitals of equal energy.
Once the co-ordinate bonds have been formed, the ion looks exactly the same as the equivalent aluminium ion. Because the iron is forming 6 bonds, the co-ordination number of the iron is 6.
CuCl 4 This is a simple example of the formation of a complex ion with a negative charge. To bond the four chloride ions as ligands, the empty 4s and 4p orbitals are used in a hybridised form to accept a lone pair of electrons from each chloride ion. Because chloride ions are bigger than water molecules, you can't fit 6 of them around the central ion - that's why you only use 4. Only one of the 4 lone pairs on each chloride ion is shown.
The other three are pointing away from the copper ion, and aren't involved in the bonding. That gives you the complex ion:.
The ion carries 2 negative charges overall. That comes from a combination of the 2 positive charges on the copper ion and the 4 negative charges from the 4 chloride ions. In this case, the co-ordination number of the copper is, of course, 4. The total number of points of attachment to the central element is termed the coordination number and this can vary from 2 to as many as 16, but is usually 6.
In simple terms, the coordination number of a complex is influenced by the relative sizes of the metal ion and the ligands and by electronic factors, such as charge which is dependent on the electronic configuration of the metal ion. Based on this, it can be seen that the bigger the charge on the central ion, the more attraction there will be for negatively charged ligands, however at the same time, the bigger the charge the smaller the ion becomes which then limits the number of groups able to coordinate.
Transition-metal complexes have been characterized with coordination numbers that range from 1 to 12, but the most common coordination numbers are 2, 4, and 6. Examples of complexes with these coordination numbers are given in the table below.
Note that the charge on the complex is always the sum of the charges on the ions or molecules that form the complex. Syllabus ref: A complex ion consists of a central transition metal ion surrounded by species atoms, molecules or ions , called ligands, which are bonded to the central metal ion by dative coordinate bonds. The whole entity may be positive, negative or even neutral, depending on the numbers and charges of the metal ion and the ligands.
Complexes are compounds, or ions, in which an atom or ion is surrounded by other species making a larger particle. The term is almost exclusively taken to mean a compound or an ion of a transition metal in which the metal ion or atom itself is surrounded by other atoms or ions. In the complex ion at the left there are six water molecules bonded to the central cobalt ion in an octahedral arrangement.
In the complex ion at the left there are four chloride ions bonded to the central copper ion in an tetrahedral arrangement. The formula of the complex is written [CuCl 4 ] There is no need for brackets around the chloride ions. The attached ions or molecules donate an electron pair to form a covalent bond to this central atom. The bonding is called dative coordinate bonding. This behaviour is characteristic of the transitions metals.
The first row transition elements have partially filled 'd' orbitals in the 3d level, but they also have empty 4p and 4d orbitals that can become involved in bonding. This allows the transition elements to form structures in which there are four, five or six attached species see ligands below.
Ligands may be molecules or ions, the most common being water, hydroxide, halogens, cyanide and ammonia. The ligands that attach to a transition metal atom depend on the local environment of the atom. In aqueous solution the vast excess of water molecules means that the most common transition metal complex is the hexaaqua complex ion. However, ligands are 'labile' in that they can become detached and exchange places with other ligands should the conditions change.
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