Application Of Coordination Compounds

  

Coordination compounds found their applications long before the establishment of inorganic chemistry. A systematic investigation of structure and bonding in coordination chemistry began with the inquisitiveness of Tassaert which was extended by distinguished chemists like Wilhelm Blomstrand, Jorgensen and Alfred Werner until the end of the. Due to tetrahedral coordination by weak-field sulfur ligands, the iron is high spin in both the Fe 3 + and Fe 2 + oxidation states, which results in similar structures for the oxidized and reduced forms of the Fe–S complexes. Consequently, only small structural changes occur after oxidation or reduction of the Fe–S center, which results in. Coordination Chemistry: Recapitulation of Werner’s Coordination theory IUPAC nomenclature of coordination compounds, isomerism in coordination compounds. With coordination numbers 4 and 6. A brief idea about chelate effect and labile and inert complexes. Valence bond theory and its application to complexes of coordination numbers 4 and 6.

Coordination complex is a structure that forms because of a collision between molecules while new bonds are formed. It is the product of a Lewis acid-base reaction in which neutral molecules or anions (called ligands) bond to a central metal atom (or ion) by coordinate covalent bonds. It consists of a central atom or ion, which is usually metallic and is called the coordination center, and a surrounding array of bound molecules or ions, that are in turn known as ligands or complexing agents. Compounds that contain a coordination complex are called coordination compounds. Many metal-containing compounds, especially those of transition metals, are coordination complexes. If the coordination complex carries a net charge, the complex is called a complex ion. A coordination complex whose center is a metal atom is called a metal complex.

Coordination complexes are so pervasive that their structures and reactions are described in many ways, sometimes confusingly. These complexes can be neutral or charged. The atom within a ligand that is bonded to the central metal atom or ion is called the donor atom. When the complex is charged, it is stabilized by neighboring counter-ions. In a typical complex, a metal ion is bonded to several donor atoms, which can be the same or different. A complex ion has a metal ion at its center with a number of other molecules or ions surrounding it. The molecules or ions surrounding the central metal ion are called ligands.

Application of coordination compounds –

Metals only exist in solution as coordination complexes, it follows then that this class of compounds is useful in a wide variety of ways. Noble metals like silver and gold are extracted from their ore by the formation of cyanide complexes – dicyanoargentite and dicyanoaurate

Bioinorganic chemistry

In bioinorganic chemistry and bioorganometallic chemistry, coordination complexes serve either structural or catalytic functions. An estimated 30% of proteins contain metal ions. Metals can be purified by the formation and subsequent decomposition of their coordination compounds. Examples include the intensely colored vitamin B12, the heme group in hemoglobin, the cytochromes, the chlorin group in chlorophyll, and carboxypeptidase, a hydrolytic enzyme important in digestion.

Industry

Homogeneous catalysis is a major application of coordination compounds for the production of organic substances. Processes include hydrogenation, hydroformylation, oxidation. (When copper sulfate solution is mixed with aqueous ammonia, a deep blue complex soluble in water is formed. This reaction is used to detect cupric ions in the salt).

Nickel, cobalt, and copper can be extracted using hydrometallurgical processes involving complex ions. They are extracted from their ores as ammine complexes. Metals can also be separated using the selective precipitation and solubility of complex ions. Cyanide is used chiefly for the extraction of gold and silver from their ores.

Application Of Coordination Compounds In Electroplating

Coordination

Platinum Metals Rev., 2008, 52, (1), 21

doi:10.1595/147106708x259497

“Medicinal Applications of Coordination Chemistry”

  • Royal Society of Chemistry,
  • Cambridge, U.K., 2007, xii + 354 pages, ISBN 978-0-85404-596-9, £89.95, U.S.$169.00
  • Reviewed by Peter J. Sadler
  • Department of Chemistry, University of Warwick,
  • Gibbet Hill Road, Coventry CV4 7AL, U.K.
  • Email: [email protected]

Inorganic compounds have been used in medicine for thousands of years, often without a known molecular basis for their mechanism of action, and with little attempt to design them. The design of coordination (metal) complexes is not an easy task. The organic chemist often deals with diamagnetic compounds which are both kinetically and thermodynamically stable, and benefits from the use of well developed speciation techniques, especially 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. For metal compounds the situation is more complicated. Ligand substitution and redox reactions can be facile, can occur over very wide timescales, and are not so easily followed by conventional techniques, especially under physiologically relevant conditions (for instance, at micromolar concentrations). But the challenge is real and worth exploring. We need new drugs with novel mechanisms of action. Inorganic chemistry offers that possibility.

Platinum Anticancer Drugs

Two areas of work have highlighted the potential of inorganic chemistry in recent years: the platinum anticancer field and gadolinium compounds, used as contrast agents in magnetic resonance imaging (MRI). Both of these are well covered in this new book. Platinum commands about forty pages. This is warranted. Platinum compounds are now the world's best-selling anticancer drugs – they have billion-dollar sales each year. If you are not familiar with atomic structure, types of chemical bonds, oxidation states, coordination geometries, isomerism, electronic structure and magnetism, then there are some one hundred pages (just over a quarter of the book) of introduction to help you, including the background on square-planar platinum complexes needed to understand the mechanism of action of the first platinum complex to be approved for clinical use: cisplatin (cis-diamminedichloroplatinum(II)).

The section on platinum, like the others, is in general well illustrated with line diagrams of chemical structures, and gives a good coverage of new developments, such as active trans complexes and potent di- and tri-Pt anticancer complexes, such as BBR3464. Not quite so good are some of the (grayscale) views of structures of DNA, proteins and their adducts, e.g. Figures 10 and 11 in Chapter 4. There is an omission concerning an intriguing feature of the structure of the adduct between guanine-guanine platinated DNA and the protein HMG1A, which is the intercalation of a protein phenylalanine side chain between the platinated guanine bases on DNA. Such an adduct probably plays a crucial role in the mechanism of action of cisplatin. But this feature is not shown in the picture on page 254; Figure 1 of this review shows an alternative view (1).

Coordination Compound Lab

Fig. 1

The insertion (intercalation) of phenylalanine-37 side-chain (grey) from the HMG protein into the hydrophobic lesion on DNA created by a cisplatin intrastrand crosslink between two adjacent guanine bases (based on the Protein Data Bank (PDB) entry 1ckt (1)). Colour key: Yellow = platinum; Dark blue = N of NH3; Red helices = HMG protein; DNA bases: Green = guanine, G; Purple = cytosine, C; Red = adenine, A; Cyan = thymine, T

Application Of Coordination Compounds In Biological Systems

Diagnostic Imaging

Application Of Coordination Compounds In Nature Products

It is a tribute to clever coordination chemistry that gram quantities of potentially toxic gadolinium ions can be safely injected into a patient undergoing an MRI scan, in fact into millions of patients each year. The Gd3+ ion binds strongly to multidentate chelated ligands, while still having sufficient room in its coordination sphere to bind and relax water. Much elegant research is being undertaken to optimise this effect: investigating the choice of the ligand donors, the size of the complex, control of rotation, water exchange rates, targeting and so on. These features are well described in thirty pages of Chapter 3, which also deals with radiopharmaceuticals, another area of much commercial interest. Much attention is deservedly focused on 99mTc, the short-lived (6 h half-life) technetium isotope-of-choice for many diagnostic imaging procedures, with its wide range of oxidation states and potential for being targeted with the right choice of ligands.

Other Metals

Coverage of other precious metals includes gold, ruthenium (currently two complexes in clinical anticancer trials), palladium (much more kinetically labile than platinum, currently the subject of research) and rhodium (anticancer potential). Surprisingly, silver is not dealt with, even though it is a very effective antibacterial agent. Washing machines containing slow-release silver are even being sold these days, to sterilise clothes as you wash them (see Samsung's SilverCare Washing Machine!). Gold drugs have been used for the treatment of difficult cases of rheumatoid arthritis for over seventy years: gold is transported by albumin in the blood by binding to the thiol at cysteine-34. This is depicted in Figure 18 on page 288, but in fact the thiol group is partially buried in a crevice and not totally exposed on the surface of the protein as the figure suggests.

Other topics covered include chelation therapy (for iron in thalassaemia, copper in Wilson's disease), vanadium as an insulin mimetic and superoxide dismutase mimics. A final chapter on design emphasises the need to control both the thermodynamics and kinetics of the reactions of metal complexes in biological (physiological) systems, in order to make real progress in this field. I missed bismuth (antiulcer drugs), antimony (antiparasitic) and arsenic (mentioned in passing, now a first-line treatment for certain types of leukaemia). Three elements with poor NMR nuclei! Missing too, except as a passing mention, is lithium for treatment of bipolar disorder (taken by more than 1 in every 1000 of the U.K. population).

Concluding Remarks

It is fortunate that the authors included a disclaimer on page vii that their information must not be relied upon to guide clinical decisions, since it says on page 11 that Phase I clinical trials involve ‘healthy volunteers’. This is not usually the case with anticancer drugs, many of which are known to be cytotoxic. For these, Phase I (which is mainly concerned with establishing a safe dose for administration) involves patients who have not responded to other treatments.

Application Of Coordination Compounds

This book will serve a useful role in teaching inorganic chemistry to both undergraduate and postgraduate students. The topic helps to ‘bring inorganic chemistry to life’, and in my experience does arouse their curiosity at all levels. It will be a useful addition to libraries, or if you shop around on the web, perhaps affordable for your own personal bookshelves.

Coordination Compound Uses

Reference

  1. U.-M. Ohndorf, M. A. Rould, Q. He, C. O. Pabo and S. J. Lippard, Nature, 1999, 399, (6737), 708 LINK http://dx.doi.org/10.1038/21460

The Reviewer

Peter Sadler obtained his B.A., M.A. and D.Phil. at the University of Oxford, U.K., and then spent two years as a Medical Research Council Research Fellow at the National Institute for Medical Research and University of Cambridge. In 1973 he was appointed as a Lecturer in Chemistry at Birkbeck College, University of London, where he subsequently became Reader in Biological Inorganic Chemistry, and then Professor of Chemistry. In 1996 he was appointed to the Crum Brown Chair of Chemistry at the University of Edinburgh, and in June 2007 took up a Chair at the University of Warwick where he is also Head of Department. He is a Fellow of the Royal Society of Edinburgh (FRSE) and the Royal Society of London (FRS). His research on platinum group metals involves the design of organometallic ruthenium and osmium anticancer complexes, and photoactivated platinum anticancer complexes.