Applications Coordination complexes

Thus in the presence of an excess of NH4+, which suppresses this forward reaction, and counteranions such as NOa" and C104, which have little tendency to coordinate, complexes such as [Hg(NH3)4] +, [Hg(L-L)2] + and even [Hg(L-L)3] + (L-L = en, bipy, phen) can be prepared. But, in the absence of such precautions, amino, or imino-compounds are likely to be formed, often together. Because of this variety of simultaneous reactions and their dependence on the precise conditions, many reactions between Hg and amines, although first performed by alchemists in the Middle Ages, remained obscure until the application of X-ray crystallography and, still more recently, spectroscopic techniques such as nmr, infrared and Raman. 

This index contains over 25 000 entries to the 6562 text pages of Volumes 1-6. The index covers general types of coordination complex, specific coordination complexes, general and specific organic compounds where their synthesis or use involves coordination complexes, types of reaction (insertion, oxidative addition, etc.), spectroscopic techniques (NMR, IR, etc.), and other topics involving coordination complexes, such as medicinal and industrial applications. 

This review deals with the chemistry and coordination complexes of isoelectronic analogues of common oxo-anions of phosphorus such as PO3, POl", RPOl" and R2POy. The article begins with a discussion of homoleptic systems in which all of the 0x0 ligands are replaced by imido (NR) groups. This is followed by an account of heteroleptic phosphorus-centered anions, including [RN(E)P(/<-NR )2P(E)NR]2-, [EP(NR)3]3-, [RP(E)(NR)2] and [R2P(E)(NR )] (E=0,S, Se, Te). The emphasis is on the wide variety of coordination modes exhibited by these poly-dentate ligands, which have both hard (NR) and soft (S, Se or Te) centers. Possible applications of their metal complexes include new catalytic systems, coordination polymers with unique properties, and novel porous materials. 

The divalent Co(salen) complex (69a) is one of the most versatile and well-studied Co coordination compounds. It has a long and well-documented history and we shall not restate this here. Recent applications of (69a) as both a synthetic oxygen carrier and as a catalyst for organic transformations are described in Sections 6.1.3.1.2 and 6.1.4.1 respectively. Isotropic shifts in the HNMR spectrum of low-spin Co(salphn) (69b) were investigated in deuterated chloroform, DMF, DMSO, and pyridine.319 Solvent-dependent isotropic shifts indicate that the single unpaired electron, delocalized over the tetradentate 7r-electron system in CHCI3, is an intrinsic property of the planar four-coordinate complex. The high-spin/low-spin equilibrium of the... 

The susceptibility of phosphites to hydrolysis limits their application as ligands for homogeneous catalysis. The fused tricyclic monophosphites derived from ca 1 i x[4]arenes260-262 form coordination complexes with palladium.263... 

There is no other vitamin which exemplifies the interdependence between the human race and microorganisms better than Vitamin B12. Mankind still relies for its very existence upon the capability of a few species of bacteria to synthesize this fascinating coordination complex. A concerted effort is being made in a number of laboratories to determine procedures for the chemical synthesis of this vitamin. However, even the most talented synthetic chemists would have to admit that the organic chemist s lament is applicable to Vitamin B12 ... 

The electron spin resonance spectrum of a free radical or coordination complex with one unpaired electron is the simplest of all forms of spectroscopy. The degeneracy of the electron spin states characterized by the quantum number, ms = 1/2, is lifted by the application of a magnetic field, and transitions between the spin levels are induced by radiation of the appropriate frequency (Figure 1.1). If unpaired electrons in radicals were indistinguishable from free electrons, the only information content of an ESR spectrum would be the integrated intensity, proportional to the radical concentration. Fortunately, an unpaired electron interacts with its environment, and the details of ESR spectra depend on the nature of those interactions. The arrow in Figure 1.1 shows the transitions induced by 0.315 cm-1 radiation. 

Structural applications range from organic, inorganic and organometallic radicals to coordination complexes and biological macromolecules containing a paramagnetic center. 

Most of the information content from ESR spectra of organometallic radicals and coordination complexes comes from dilute single-crystal spectra or frozen solution spectra. Nonetheless, there are some bits of information and applications that come uniquely from isotropic spectra, and we discuss those aspects in this chapter. 

This volume aims to give as complete a coverage of the real and possible applications of coordination complexes as is possible in a single volume. It is far more wide-ranging in its coverage than the related volume on applications in the first edition of CCC (1987). 

The chapters cover the following areas (i) use of coordination complexes in all types of catalysis (Chapters 1-11) (ii) applications related to the optical properties of coordination complexes, which covers fields as diverse as solar cells, nonlinear optics, display devices, pigments and dyes, and optical data storage (Chapters 12-16) (iii) hydrometallurgical extraction (Chapter 17) (iv) medicinal and biomedical applications of coordination complexes, including both imaging and therapy (Chapters 18-22) and (v) use of coordination complexes as precursors to semiconductor films and nanoparticles (Chapter 23). As such, the material in this volume ranges from solid-state physics to biochemistry. 

Thirdly, some obvious applications of coordination chemistry are omitted from this volume if they are better treated elsewhere. This is the case when a specific application is heavily associated with one particular element or group of elements, to the extent that the application is more appropriately discussed in the section on that element. Essentially all of the coordination chemistry of technetium, for example, relates to its use in radioimmunoimaging inclusion of this in Chapter 20 of this volume would have left the chapter on technetium in Volume 5 almost empty. For the same reason, the applications of actinide coordination complexes to purification, recovery,... 

The Lever treatment is of wider application in that it can be extended to (six-coordinate) complexes which have only the same central metal ion in common but totally different ligands. Consider the series of iron(II) complexes in Table 6.4b... 

There are four naturally occurring isotopes of iron ( Fe 5.82%, Fe 91.66%, Fe 2.19%, Fe 0.33%), and nine others are known. The most abundant isotope ( Fe) is the most stable nuclear configuration of all the elements in terms of nuclear binding energy per nucleon. This stability, in terms of nuclear equilibrium established in the last moments of supernova events, explains the widespread occurrence of iron in the cosmos. The isotope Fe has practical applications, most notably in Mossbauer spectroscopy, which has been widely exploited to characterize iron coordination complexes. 

The high generality of Lever Eq. (16) also brings some drawbacks. In order to be applicable to all the six-coordinate complexes with a certain redox... 

One of the most studied mononuclear systems that usually leads to supramolecular networks and that also exhibits very rich photophysics and photochemistry is the [Au (CN)2] anion. This complex is among the most stable two-coordinate complexes of the transition ions, with a stability constant of 1037 [9], being reasonably stable to air, moisture, temperature and light, which could make it appropriate for practical applications. 

The most common and best known chelant is ethylenediaminetetraacetic acid (EDTA). The related compounds diethylenetriaminepentaacetic acid (DTPA) and nitrilotriacetic acid (NTA) are also well known (Figure 10.2). EDTA is a powerful chelant that complexes strongly with most metal ions to form six-coordinate complexes. It has therefore become the first choice in most applications. Indeed, a search of the bathroom cabinet will spot EDTA on the ingredient list of many personal care formulations. DTPA is also a powerful chelant, but tends to be used more often in industrial settings. NTA has only four binding sites and is used more often where hardness ions require control, such as in cleaning, for example, hard surface cleaners, dishwashing, and the dairy industry. 

The photographic industry continues to dominate in the industrial applications of silver complexes, especially in relation to halogen compounds, and a vast amount of literature each year is concerned with this field. Photographic applications of coordination complexes are covered separately in Chapter 59 and will not be dealt with in depth here. 

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