Coordination chemistry pairings

The choice of metal ion in this work is interesting since it has been known for a considerable time that Ag+ is a rare example of a d-block metal ion that does not disrupt the duplex DNA structure (172,173). Rationalization of this effect has tended to focus on the possible base-pair crosslinking due to the preferred linear coordination geometry of Ag1 ions (174). The importance of Ag+ DNA coordination chemistry to the procedure described is not clear. However, reports that other metal ions, e.g., Pdri (175), can be plated to DNA to fabricate metallic wires (Fig. 51) suggests that this may not be essential. 

The coordination chemistry of diazaphospholes has attracted much attention during the last decade. Among various categories of diazaphospholes, coordination behavior of [1,2,3]- and [l,2,4]diazaphospholes has been investigated. They provide a variety of ligating sites, in addition to the phosphorus and =N- lone pairs n coordination of the type if and if is also possible. In 4-phosphino-[ 1,2,3] diazaphospholes, coordination takes place via exocyclic phosphino phosphorus. Accordingly, complexation reactions can be subdivided into two categories-... 

Perhaps the greatest area in which the Lewis acid-base approach is most useful is that of coordination chemistry. In the formation of coordination compounds, Lewis acids such as Cr3+, Co3+, Pt2+, or Ag+ bind to a certain number (usually 2, 4, or 6) of groups as a result of electron pair donation and acceptance. Typical electron pair donors include H20, NH3, F , CN , and many other molecules and ions. The products, known as coordination compounds or coordination complexes, have definite structures that are predictable in terms of principles of bonding. Because of the importance of this area of inorganic chemistry, Chapters 16 through 22 in this book are devoted to coordination chemistry. 

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. 

Ligands having a lone electron pair on the phosphorus atom play a key role in transition-metal coordination chemistry of today. The range of complexes that can be produced by phosphorus donors is unparalleled in coordination chemistry. They are ca-... 

The coordination numbers of metal ions range from I, as in ion pairs such as Na CI- in the vapor phase, to 12 in some mixed metal oxides. The lower limit, I. is barely within the realm of coordination chemistry, since the Na+CI km pair would not normally be considered a coordination compound, and there are few other examples. Likewise, the upper limit of 12 is not particularly important since it is rarely encountered in discrete molecules, and the treatment of solid crystal lattices such as hexagonal BaTiOj and perovskite1 as coordination compounds is not done frequently. The lowest and highest coordination numbers found in typical coordination compounds are 2 and 9 with the intermediate number 6 being the most important. 

The first attempts to interpret Werner s views on an electronic basis were made in 1923 by Nevil Vincent Sidgwick (1873—1952) and Thomas Martin Lowry (1874—1936).103 Sidgwick s initial concern was to explain Werner s coordination number in terms of the sizes of the sub-groups of electrons in the Bohr atom.104 He soon developed the attempt to systematize coordination numbers into his concept of the effective atomic number (EAN).105 He considered ligands to be Lewis bases which donated electrons (usually one pair per ligand) to the metal ion, which thus behaves as a Lewis acid. Ions tend to add electrons by this process until the EAN (the sum of the electrons on the metal ion plus the electrons donated by the ligand) of the next noble gas is achieved. Today the EAN rule is of little theoretical importance. Although a number of elements obey it, there are many important stable exceptions. Nevertheless, it is extremely useful as a predictive rule in one area of coordination chemistry, that of metal carbonyls and nitrosyls. 

The coordination chemistry of macrocyclic ligands has been extensively studied and aspects of isomerism have been considered in numerous systems.241 Methods whereby two diastereomers of complexes of tetra- N-methylcyclam may be isolated have been discussed previously.184 This, however, is a relatively simple system and it is usually necessary to consider isomerism due to the presence of asymmetric atoms in the chelate arms, as well as that due to asymmetric donor atoms that may be rendered stable to inversion by coordination. An example of a system exhibiting this level of complexity is afforded by the nickel(II) complexes of the macrocyclic ligands generated by reduction of the readily prepared macrocycle (46). These ligands contain two asymmetric carbon atoms and four asymmetric nitrogen atoms but, because AT-inversion is rapid, it is conventional to consider that only three separable stereoisomers exist. There is an enantiomeric pair, (47a) and (47b), which constitutes the racemic isomer (R, R ), and an achiral (R, S ) diastereomer (47c), the meso isomer. 

LEWIS, GILBERT N. 11875-1946). An American chemist, native of Massachusetts, professor of chemistry at MIT from 1905 to 1912 after which he became dean of chemistry at the University of California at Bcikeley. His inosi creative contribution was the eleciroh-pair theory of acids and bases, which laid the groundwork lor coordination chemistry. He was also a leading authority on thermodynamics. 

Classical coordination chemistry has been developed in terms of the traditional ligands1,2 such as water, ammonia and the chloride anion, all of which contain at least one lone pair of electrons which may be used in the coordination of the ligand to a metal by the formation of a dative covalent bond. 

The coordination chemistry of the dithiocarbimates (80), with R = Me or Ph, has been described for complexes of Ni and Pr.1,40 Dubois et al. reported the synthesis of (81) 91 complex (82), in which each Mo atom has one double bonded and two bridged sulfur atoms, was reacted with two moles of RNC. The isocyanide molecules bridge two pairs of sulfur atoms equally. 

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