Coordination chemistry linear geometries

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. 

As a consequence of its electronic configuration, a variety of coordination numbers and geometries have been observed for copper(I) compounds, especially for inorganic representatives (see Fig. 1.3) [32]. In the organometallic chemistry of copper, the linear and trigonal coordination geometries in particular, though distorted towards T-shaped, are frequently encountered. 

With almost all of the conceivable coordination chemistry of the expanded porphyrins still left to be explored, it cannot be over-stres that the potential for new chemistry is enormous. This is i rticularly true when account is made of the fact that the chemistry of the metalloporphyrins has played a dominant role in modern inorganic chemistry. What with the possibility to enhance the stability of imusual coordination geometries (and, perhaps oxidations states) and the ability to form stable coordination complexes with a variety of unusual cations including those of the lanthanide and actinide series, the potential for new inorganic and organometallic discoveries are almost unlimited. For instance, as with the porphyrins, one may envision linear arrays of stacked expanded porphyrin macrocycles which may have unique conducting properties and/or which could display beneficial super- or semiconducting capabilities. Here, of course, the ability to coordinate not only to cations but also to anions could prove to be of tremendous utility. 

In terms of its coordination chemistry, the silver(I) ion is typically characterized as soft . Although originally believed to only bind ligands in a linear arrangement, it was soon shown that it can adopt a variety of coordination environments, the most common one being a four-coordinate tetrahedral geometry. Square-planar complexes are not rare, and various silver(I) cluster complexes also contain three-and five-coordinate sUver(I) ions. 

The stractural chemistry of actinides is very diverse due to the possibility of different oxidation states and the richness of actinide coordination geometries. Whereas actiiudes in lower oxidation states sometimes mimic rare earth elements, actinides in higher oxidation states possess unique coordination chemistry, due to the tendency to form linear actinyl ions. The reviews in this book are written by specialists in their fields and the subjects range from low-valence actinide compoimds to actinide-based metal-orgaiuc frameworks. The active participation of Russian authors provides overviews of some activities undertaken by scientists in the former Soviet Uiuon. Their results are sometimes not well known to western readers because of the relatively closed nature of works in this field during the Cold War years. 

These model complexes do not include an interstitial atom nor do they capture the geometry of the central iron core of the cofactor which recent calculations point to as vital for nitrogenase activity [73-76]. One possibility is that the central atom is a nitride if this is so, then the coordination geometry is unprecedented in small-molecule model chemistry of iron nitrides. Holm and coworkers have recently begun to examine the coordination chemistry of iron nitrides to see if a nitride which bridges six iron centers can be obtained [96]. Literature precedent shows ample evidence for linear Fe-N-Fe bridges for octa-hedrally coordinated iron [97-100] and, more recently, a bent Fe-N-Fe bridge for pseudotetrahedral iron centers from our laboratory at Caltech vide infra) [89,... 

The potential carbodicarbene C(C(NMe2)2 2 has been known for a long time but no complex has been reported [101, 102]. It adopts a linear allene geometry in the free state but according to theoretical analysis exhibits a strong nucleophilic central carbon atom [4, 97] and can be seen as an allene with a hidden divalent carbon(O) character emerging in the presence of electron deficient electrophiles. Based on these findings a new field of chemistry will be opened and the number of compounds with a coordination mode should increase in the future. 

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