Chemistry coordination

3 Bonding in Coordination Compounds Crystal Field Theory 

Although the Consumer Product Safety Commission (CPSC) banned the residential use of lead-based paint in 1978, millions of children remain at risk for exposure to lead from deteriorating paint in older homes. Lead poisoning is especially harmful to children under the age of 5 years because it interferes with growth and development and it has been shown to lower IQ. Symptoms of chronic exposure to lead include diminished appetite, nausea, malaise, and convulsions. Blood lead level fBLL), expressed as micrograms per deciliter (p.g/dL), is used to monitor the effect of chronic exposure. A BLL 10 p.g/dL is considered normal a BLL 45 xg/dL requires medical and environmental intervention. At high levels ( 70 p.g/dL), lead can cause seizures, coma, and death. 

Ilian 1QLD DUTCH Proiess ttWIe Lead. 

In This Chapter You, Will Learn about the properties of coordination compounds and how, through the use of chelates, coordination chemistry is used to solve a variety of medical and other societal problems. 

Lead paint, known for its brightness and durability, was commonly used to paint homes, fences, and interior walls. Its use in homes was banned in 1978 because of the health risks associated with exposure to lead. 

At the end of this chapter, you will be able to answer questions about some important coordination compounds Page 939]. 

Student Annotation We can use the term coordinatbn complex lo refer to a compound, such as Fe(CO)s, or to a complex ion. 

Coordination compounds contain coordinate covalent bonds [ Section 8.8] formed by the reactions of metal ions with gronps of anions or polar molecules. The metal ion in these kinds of reactions acts as a Lewis acid, accepting electrons, whereas the anions or polar molecnles act as Lewis bases, donating pairs of electrons to form bonds to the metal ion. Thns, a coordinate covalent bond is a covalent bond in which one of the atoms donates both of the electrons that constitute the bond. Often a coordination compound consists of a complex ion and one or more counter ions. In writing formulas for such coordination compoimds, we use square brackets to separate the complex ion from the counter ion. 

Robertson, Physical chemistry , in Recent Developments in the History of Chemistry, ed. C. A. Russell, Royal Society of Chemistry, London, 1985, pp. 153-176. 

Root-Bemstein, The Ionists Founding Physical Chemistry, 1872-1890 , Ph.D. dissertation, Princeton University, 1980 Univ. Microfilms order no. 81-01554 

Partington, A History of Chemistry, 4 vols, Macmillan, London, 1961-1970. 

Laidler, The World of Physical Chemistry, Oxford University Press, New York, 1993. 

Laidler, The Henry Marshall Tory medal address the second half-century of physical chemistry , Trans. Roy. Soc. Can., 1987, 2, 181-186. 

The chemistry of coordination compounds comprises an area of chemistry that spans the entire spectrum from theoretical work on bonding to the synthesis of organometallic compounds. The essential feature of coordination compounds is that they involve coordinate bonds between Lewis acids and bases. Metal atoms or ions function as the Lewis acids, and the range of Lewis bases (electron pair donors) can include almost any species that has one or more unshared pairs of electrons. Electron pair donors include neutral molecules such as H20, NH3, CO, phosphines, pyridine, N2, 02, H2, and ethyl-enediamine, (H2NCH2CH2NH2). Most anions, such as OH-, Cl-, C2042-, and 11, contain unshared pairs of electrons that can be donated to Lewis acids to form coordinate bonds. The scope of coordination chemistry is indeed very broad and interdisciplinary. 

Some of the important types of coordination compounds occur in biological systems (for example, heme and chlorophyll). There are also significant applications of coordination compounds that involve their use as catalysts. The formation of coordination compounds provides the basis for several techniques in analytical chemistry. Because of the relevance of this area, an understanding of the basic theories and principles of coordination chemistry is essential for work in many related fields of chemistry. In the next few chapters, an introduction will be given to the basic principles of the chemistry of coordination compounds. 

The transition-metal coordination chemistry of a number of deprotonated iHc.vo-octaal kylporphyrinogens, particularly /He.vo-octaethylcalixldlpyrrole 5 has been studied in detail by Floriani and coworkers. - The results ot their extensive work are detailed elsewhere in this book.  

A recurrent theme in the coordination chemistry of crown thioethers concerns the interplay between conformational preferences of the ligands and their coordinative behavior. In particular, the structures of complexes result from a compromise between the conformational preferences of the ligands and the electronic requirements of the metal ion. Crown thioethers such as 12S4 show a diminished propensity for chelation because of the exodentate orientation of the S atoms in the free ligand. Exodentate structures reflect the antipathy of most crown thioethers to chelation. As a consequence, complexes with incomplete chelation by the ligand form a substantial fraction of this review. 

This observation in turn highlights the importance of charge neutralization in thioether coordination chemistry. Thioethers fail to neutralize charge on metal ions 

Thus the electronic consequences of thioether coordination result from the interplay of both charge neutralization as well as ti-acidity. The magnitude of these effects depends on the number of thioethers in the coordination sphere. This is particularly important for charge neutralization effects, which clearly will be most pronounced in the absence of anionic auxiliary ligands. 

The oxophilic nature of Sml2 is in many cases a highly beneficial quality The coordination of two or more oxygenated reactive centres to samarium in both radical and ionic processes mediated by the reagent can often lead to high levels of diastereoselectivity in the formation of products. The coordination of Sm(II) and Sm(III) to oxygen donors on the substrate, solvent or cosolvent is a common theme that runs through each of the subsequent chapters. 

There has been a growing interest for the structural study of disordered or amorphous coordination complexes in the past few years. Thus, particular situations account for this interest  

An example of the previous situation is enlightened by the case of the Cu Ni p-oxalato chain studied by Verdaguer et al. The aim of this study is to establish a structural model of this ordered bimetallic chain in order to explain the magnetic properties. As it has been impossible to obtain single crystals, the EXAFS technique has been used at both the copper and the nickel edges. 

EXAFS data were recorded at LURE-DCl at room temperature and 30 K, for the (CuNi) and (CuZn) bimetallic chains and for the (Cu), (Ni) and (Zn) homometallic compounds. The Fourier transform spectra are shown in Fig. 11. 

A very similar study, with the same motivation, has been performed by Verdaguer et al, on copper (II) chloranilato and bromanilato complexes Two structures were proposed for the compound Cu(CgO X2), as shown in Fig. 13 for X = H. 

EXAFS data were collected at the Cu and Br edges. The fitting results give the following distances Cu—O = 1.95 A Cu—C = 2.6 A Br — C = 1.86 A Br—Cu = 5.06 A Br—Br = 6.55 A. These results are quite compatible with a planar ribbon structure. Moreover, the authors demonstrate that a planar layer structure or a bent ribbon structure can be ruled out as incompatible with the Cu—O and Cu—C distances. 

Exciting developments have occurred in the coordination chemistry of the alkali metals during the last few years that have completely rejuvenated what appeared to be a largely predictable and worked-out area of chemistry. Conventional beliefs had reinforced the predominant impression of very weak coordinating ability, and had rationalized this in terms of the relatively large size and low charge of the cations M+. On this view, stability of coordination complexes should diminish in the sequence Li Na K Rb Cs, and this is frequently observed, though the reverse sequence is also known for the formation constants of, for example, the weak complexes with sulfate, peroxosulfate, thiosulfate and the hexacyanoferrates in aqueous solutions. 

They probably all contain the tetrahedral ion [Li(OPPh3)4]+ which was established by X-ray crystallography for the compound Lil.SPhsPO the fifth molecule of PhaPO is uncoordinated. 

In recent years this simple picture has been completely transformed and it is now recognized that the alkali metals have a rich and extremely varied coordination chemistry which frequently transcends even that of the transition metals. The efflorescence is due to several factors such as the emerging molecular chemistry of lithium in particular, the imaginative use of bulky ligands, the burgeoning numbers of metal amides, alkoxides, enolates and organometallic compounds, and the exploitation of multidentate 

5 trigonal-bipyramidal [LiBr(phen)2].Pr OH Br equatorial, one N from each phen axial N-Li-N 169° PFOH uncoordinated 52 

Solid State Chem. 29, 379-92 (1979), and refs, therein. 

A versatile route for the gas-phase synthesis of various gold(I) complexes is provided by the reaction of Au+ with hexafluorobenzene. While IE F ) = 9.91 eV is large enough to prevent ET, C6F6 has a sufficient number of rovibronic states to allow for efficient formation of the Au(C6F6)+ complex via radiative stabilization in the low-pressure regime according to Reaction (7.5) (Schroder et al. 1995)  

Lithium, Sodium, Potassium, Rubidium, Caesium and Francium Ch. 4 

6 octahedral LiX NaCl-type, X = H, F, Cl, Br, I. Also LilOs LiNOs (calcite-type) LiAlSl206 (spodumene)  

Ir complex as the red emitter. Cyclometallated Ru complexes may have potential as photosensitizers for solar cells. Organometallic drugs are also on the horizon. 

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Halpern J, Riley D P, Chan A S C and Pluth J J 1977 Novel coordination chemistry and catalytic properties of cationic 1,2-bis(diphenylphosphino)ethanerhodium(l) complexes J. Am. Chem. Soo. 99 8055-7... 

This thesis contributes to the knowledge of catalysis in water, us it describes an explorative journey in the, at the start of the research, unh odded field of catalysis of Diels-Alder reactions in aqueous media. The discussion will touch on organic chemistry, coordination chemistry and colloid chemistry, largely depending upon the physical-organic approach of structural variation for the elucidation of the underlying mechanisms and principles of the observed phenomena. 

To our knowledge, the results presented in this chapter provide the first example of enantioselective Lewis-acid catalysis of an organic reaction in water. This discovery opens the possibility of employing the knowledge and techniques from aqueous coordination chemistry in enantioselective catalysis. This work represents an interface of two disciplines hitherto not strongly connected. 

Laurie, S. H.In Comprehensive Coordination Chemistry, Wilkinson, G., Gillard, R. D., McCleverty, J. A. lids. Pergamon Press Oxford, 1997 pp 739... 

Of all the work described in this thesis, this discovery is probably the most significant. Given the fact that the arene - arene interactions underlying the observed enantioselectivity of ftie Diels-Alder reactions described in Chapter 3 are also encountered in other organic reactions, we infer that, in the near future, the beneficial influence of water on enantioselectivity can also be extended to these transformations. Moreover, the fact that water can now be used as a solvent for enantioselective Lewis-add catalysed reactions facilitates mechanistic studies of these processes, because the number of equilibria that need to be considered is reduced Furthermore, knowledge and techniques from aqueous coordination chemistry can now be used directly in enantioselective catalysis. 

Quantum Chemistry The Challenge of transition MetaLs and Coordination Chemistry A. Veillard, Ed., D. Reidel, Dordrecht (1986). 

S. Kitschnei, ed.. Coordination Chemistry Papers Presented in Honor of Prof. John C. Bailar, Jr., Plenum Press, New York, 1969, p. 108. 

L. J. Bouchei, ia G. A. Melson, ed.. Coordination Chemistry ofMacroyclic Compounds, Plenum Publishing Coip., New Yoik, 1979, pp. 517—539. 

There are several exceUent sources of information about the platinum-group metals. The exceUent reference work G. Wilkinson, R. D. GiUard, and J. A. McCleverty, eds.. Comprehensive Coordination Chemistry Pergamon Press, Oxford, U.K., 1987, contains iadividual chapters devoted to descriptive chemistry of each element. 

The majority of U(V1) coordination chemistry has been explored with the trans-ddo s.o uranyl cation, UO " 2- The simplest complexes are ammonia adducts, of importance because of the ease of their synthesis and their versatihty as starting materials for other complexes. In addition to ammonia, many of the ligand types mentioned ia the iatroduction have been complexed with U(V1) and usually have coordination numbers of either 6 or 8. As a result of these coordination environments a majority of the complexes have an octahedral or hexagonal bipyramidal coordination environment. Examples iuclude U02X2L (X = hahde, OR, NO3, RCO2, L = NH3, primary, secondary, and tertiary amines, py n = 2-4), U02(N03)2L (L = en, diamiaobenzene n = 1, 2). The use of thiocyanates has lead to the isolation of typically 6 or 8 coordinate neutral and anionic species, ie, [U02(NCS)J j)/H20 (x = 2-5). 

Coordination compounds of vanadium are mainly based on six coordination, in which vanadium has a pseudooctahedral stmcture. Coordination number four is typical of many vanadates. Coordination numbers five and eight also are known for vanadium compounds, but numbers less than four have not been reported. The coordination chemistry of vanadium has been extensively reviewed (8—12) (see Coordination compounds). 

The chemistry of Cr(III) in aqueous solution is coordination chemistry (see Coordination compounds). It is dominated by the formation of kineticaHy inert, octahedral complexes. The bonding can be described by Ss]] hybridization, and HteraHy thousands of complexes have been prepared. The kinetic inertness results from the electronic configuration of the Cr ion (41). This type of orbital charge distribution makes ligand displacement and... 

Cobalt exists in the +2 or +3 valence states for the majority of its compounds and complexes. A multitude of complexes of the cobalt(III) ion [22541-63-5] exist, but few stable simple salts are known (2). Werner s discovery and detailed studies of the cobalt(III) ammine complexes contributed gready to modem coordination chemistry and understanding of ligand exchange (3). Octahedral stereochemistries are the most common for the cobalt(II) ion [22541-53-3] as well as for cobalt(III). Cobalt(II) forms numerous simple compounds and complexes, most of which are octahedral or tetrahedral in nature cobalt(II) forms more tetrahedral complexes than other transition-metal ions. Because of the small stabiUty difference between octahedral and tetrahedral complexes of cobalt(II), both can be found in equiUbrium for a number of complexes. Typically, octahedral cobalt(II) salts and complexes are pink to brownish red most of the tetrahedral Co(II) species are blue (see Coordination compounds). 

The quest for a comprehensible theory of coordination chemistry has given rise to the use of valence-bond, crystal-field, hgand-field, and molecular-otbital... 

Steric Selectivity. In addition to the normal regularities that can be rationalized by electronic considerations, steric factors are important in coordination chemistry. To illustrate, 8-hydroxyquinoline, or 8-quinolinol (Hq) [148-24-3J, at 100°C precipitates both Mg " and AE" from aqueous solution as hydrated Mg(q)2 (formulated as Mg(q)2(H20)2 [56531 -18-1]) and as Al(q)3 [2085-33-8] respectively. 2-Meth54-8-hydroxyquinohne [826-81-3] (6),... 

J. C. Bailar, Jr., ed.. Chemistry of Coordination Compounds, JiCS Monograph /i/. Reinhold Pubhshiag Corp., New York, 1956. Dated but very good on the historical and classical aspects of coordination chemistry. 

F. Basolo and R. C. Johnson, Coordination Chemistry, 2nd ed., Sci. Revs., Northwood, UK, 1986. Easy-to-read paperback on coordination chemistry suitable for anyone who has studied basic chemistry. 

Trofimenko Coordination chemistry of pyrazole ligands 72CRV497... 

K. Dehnicke and U. Muller, Coordination Chemistry of S2N2, Transition Met. Chem., 10, 361 (1985). 

K. K. Pandey, Coordination Chemistry of Thionitr osyl, Thiazate, Disulfidothionitrute, Sulfur Monoxide and Disulfur Monoxide, Prog. Inorg. Chem., 40, 445 (1992). 

Monomeric sulfur diimides have an extensive coordination chemistry as might be anticipated from the availability of three potential donor sites and two r-bonds. In addition, they are prone to fragmentation to produce thionitroso and, subsequently, sulfido and imido ligands. Under mild conditions with suitable coordinatively unsaturated metal... 

Although redox processes are sometimes observed in metathetical reactions with metal halides, the pyramidal dianion [Te(NtBu)3] has a rich coordination chemistry (Scheme 10.8). For example, the reaction... 

Even the H atom itself can form compounds in which its coordination number (CN) is not just 1 (as expected) but also 2, 3, 4, 5 or even 6. A rich and unexpectedly varied coordination chemistry is thus emerging. We shall deal with the H atom first and then with the H2 molecule. 

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