Coordination-chemical synthesis

Dendritic building blocks having the nature of complex ligands can coordinate with a central metal unit [29]. Such self-assembly opens up direct access to metallodendrimers (see also Section 4.1.7). It should, however, not go unmentioned in this context that the strong Ru2+ bond to the bipyridine nitrogen -although non-covalent - is not regarded as supramolecular by some chemists because of its lack of reversibility. That is why we consider it from a coordination-chemical viewpoint [30]. 

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Li Q, Walter EC, van der Veer WE, Murray BJ, Newberg JT, Bohannan EW, Switzer JA, Hemminger JC, Penner RM (2005) Molybdenum disulfide nanowires and nanoribbons by electrochemical/chemical synthesis. J Phys Chem B 109 3169-3182 Tenne R, Homyonfer M, Feldman Y (1998) Nanoparticles of layered compounds with hollow cage structures (inorganic fuUerene-like structures). Chem Mater 10 3225-3238 Shibahara T (1993) Syntheses of sulphur-bridged molybdenum and tungsten coordination compounds. Coord Chem Rev 123 73-147... 

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 ... 

Lenhert and Hodgkin (15) revealed with X-ray diffraction techniques that 5 -deoxyadenosylcobalamin (Bi2-coenzyme) contained a cobalt-carbon o-bond (Fig. 3). The discovery of this stable Co—C-tr-bond interested coordination chemists, and the search for methods of synthesizing coen-zyme-Bi2 together with analogous alkyl-cobalt corrinoids from Vitamin B12 was started. In short order the partial chemical synthesis of 5 -de-oxyadenosylcobalamin was worked out in Smith s laboratory (22), and the chemical synthesis of methylcobalamin provided a second B 12-coenzyme which was found to be active in methyl-transfer enzymes (23). A general reaction for the synthesis of alkylcorrinoids is shown in Fig. 4. 

Reports on the coordination chemistry of A-heterocyclic carbene-containing metal complexes started to appear as long ago as 1968,50,51 while metal-free carbenes have only been isolated very recently.52 In view of the fact that the general chemistry and applications of organic carbenes and related metal complexes in chemical synthesis have been reviewed several times recently,53-57 examples limited only to those carbene complexes with silver(i) have been discussed. Nevertheless, it is worth mentioning that the developments in silver(i) A-heterocyclic carbenes have also been reviewed recently by Lin.5... 

Supercritical water (SCW) presents a unique combination of aqueous and non-aqueous character, thus being able to replace an organic solvent in certain kinds of chemical synthesis. In order to allow for a better understanding of the particular properties of SCW and of its influence on the rate of chemical reactions, molecular dynamics computer simulations were used to determine the free energy of the SN2 substitution reaction of Cl- and CH3C1 in SCW as a function of the reaction coordinate [216]. The free energy surface of this reaction was compared with that for the gas-phase and ambient water (AW) [248], In the gas phase, an ion-dipole complex and a symmetric transition... 

A number of synthetic methods have been successfully developed for the synthesis of block copolymers. They include polycondensation, anionic, cationic, coordinative and free-radical polymerizations and also mechano-chemical synthesis. Despite the exceptional amount of attention paid to the prospects of various catalytic systems, radical polymerization has not lost any of its importance, particularly in this area. Its competitiveness with other methods of conducting polymerization are attributable to the simplicity of the mechanism and good reproducibility. Actually, the extensive use of free radical polymerization in practice is well understood when considering the ease of the process, the soft processable conditions of vacuum and temperature, the fact that reactants do not need to be highly pure and the absence of residual catalyst in the final product. Thus, it can be easily understood that more than 50% of all plastics have been produced industrially via radical polymerization. 

Sakamoto, M., Manseki, K., and Okawa, H. (2001) d—f Heteronuclear complexes synthesis, structures and physicochemical aspects. Coordination Chemical Reviews, 219, 379 14. 

Wong, W.-K., Zhu, X., and Wong, W.-Y. (2007) Synthesis, structure, reactivity and photoluminescence of lanthanide(lll) monoporphyrinate complexes. Coordination Chemical Reviews, 251, 2386. 

This review is not intended to provide an exhaustive picture of photoinduced electron (and energy) transfer in covalently linked inorganic systems. It should demonstrate, however, that this is an active and attractive field of research. Coordination compounds, because of their intrinsic combinatory nature, offer wide possibilities in terms of tailoring spectroscopic, redox, and photophysical properties of molecular components. The continuing progress in chemical synthesis provides a variety of... 

These methods for achieving slow diffusion of reactant solutions are not just applicable in the initial chemical synthesis of a desired product. For ionic coordination compounds, they can also be used when it is desirable to exchange the counter-ion to obtain potentially better quality crystals or to reduce the solubility by better size-matching of the ions. The initially obtained complex salt is in one solution, and a simple salt of the new counter-ion is in the other. Slow mixing of these two may be carried out by any of the techniques described here, or by simple layering of one solution over the other as in Section 1.28.4 obviously, vapor diffusion is not appropriate for this purpose, as it does not transfer the solutes between the two liquids. 

A process even more challenging than structure determination is the prediction of a crystal structure without the use of experimental information relevant to that particular structure. This process, called crystal structure prediction CSP), would allow one to announce a crystal structure before any confirmation by chemical synthesis or discovery in nature. The outcome of CSP is the prediction of the atomic coordinates of the structural model, together with the space group and cell constant specifications. The relation of CSP with powder diffraction relies on the fact that a powder pattern can be calculated using this outcome, which could further be used to identify a real compound not yet characterized. 

Suffice to say that kinetics and thermodynamics, in combination, govern all of our chemical reactions, but obviously tempered by what exactly is available chemically to react. We shall examine stability and reactions of coordination complexes in more detail in Chapter 5, and the application of these in chemical synthesis is met in Chapter 6. 

Increased sophistication in chemical synthesis has led to the development of a wide range of molecules which can wrap up or encapsulate metal ions (as well as, in some cases, even whole small molecules). A range of topologies (or three-dimensional shapes) has been devised for accommodation of either metal ions with different preferred coordination numbers or small molecules. The former usually involve covalent bonds, the latter weaker nonco-valent interactions (such as hydrogen bonds). Developing functionality for encapsulated... 

We can categorize reactions in a number of ways. So far, we have done so in terms of rate (how fast or slow). This approach, however, tells us nothing about what is happening in a reaction or how a particular reaction occurs. We shall now define reactions in terms of what happens. We shall explore examples of the following reactions in Chapter 6, when describing examples of chemical synthesis in coordination chemistry. 

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