Metal-nitrogen bonding

Several types of nitrogen substituents occur in known dye stmetures. The most useful are the acid-substituted alkyl N-substituents such as sulfopropyl, which provide desirable solubiUty and adsorption characteristics for practical cyanine and merocyanine sensitizers. Patents in this area are numerous. Other types of substituents include N-aryl groups, heterocycHc substituents, and complexes of dye bases with metal ions (iridium, platinum, zinc, copper, nickel). Heteroatom substituents directly bonded to nitrogen (N—O, N—NR2, N—OR) provide photochemically reactive dyes. 

Two types of NO coordination to ruthenium are known linear Ru-N—O 180° and bent, Ru-N-O 120°. Since NO+ is isoelectronic with CO, linear Ru-N-O bonding is generally treated as coordination of NO+, with bent coordination corresponding to NO- thus, in the former an electron has initially been donated from NO to Ru, as well as the donation of the lone pair, whereas in the latter an electron is donated from the ruthenium to NO (making it NO-) followed by donation of the lone pair from N. Though an oversimplification, this view allows a rationale of metal-nitrogen bond lengths, as with the Ru—NO+ model 7r-donation is important and a shorter Ru—NO bond is predicted - and, in fact, observed. 

The transition metal-nitrogen multiple bond. K. Dehnicke and J. Strahle, Angew. Chem., Int. Ed. Engl., 1981, 20, 413-426 (124). 

One-electron oxidation of the vinylidene complex transforms it from an Fe=C axially symmetric Fe(ll) carbene to an Fe(lll) complex where the vinylidene carbon bridges between iron and a pyrrole nitrogen. Cobalt and nickel porphyrin carbene complexes adopt this latter structure, with the carbene fragment formally inserted into the metal-nitrogen bond. The difference between the two types of metalloporphyrin carbene, and the conversion of one type to the other by oxidation in the case of iron, has been considered in a theoretical study. The comparison is especially interesting for the iron(ll) and cobalt(lll) carbene complexes Fe(Por)CR2 and Co(Por)(CR2) which both contain metal centers yet adopt... 

In this review, CPOs constructed by covalent bonds are mainly focused on however, stable coordination bonds comparable to the stability of the covalent bonds have potential for future enhanced molecular design of novel CPOs. One representative is the bond between pyridine-type nitrogen and metal, which is widely used in supramolecular chemistry, that is, the cyclic supramolecular formation reaction between pyridine-substituted porphyrin and metal salts (Fig. 6d) [27,28]. Palladium salts are frequently used as the metal salts. From the viewpoint of the hard and soft acid and base theory (HSAB), this N-Pd coordination bond is a well-balanced combination, because the bonds between nitrogen and other group X metals, N-Ni and Ni-Pt coordination bonds, are too weak and too strong to obtain the desired CPOs, respectively. For the former, the supramolecular architectures tend to dissociate into pieces in the solution state, and for the latter. 

While metal-nitrogen and metal-oxygen bonded compounds dominate nucleobase coordination chemistry, examples in which metal-carbon bonds are formed have been identified. Early studies on the synthesis of metal-labeled DNA demonstrated that nucleotide-triphosphates, UTP, CTP, dUTP, and dCTP, can undergo mercury modification at C5 (82,83). The UTP derivative was also shown to act as a substrate for RNA polymerase in the presence of mercaptans (83). Later, guano-sine was shown to undergo mercury modification at C8 though, in this case, the purine was multiply substituted, 21 (84). 

Tables 15 and 16 show the absorption maxima of some metal complexes of benzothiazolyl-substituted formazans 230 and 231.283 The wavelengths are metal ion dependent, making formazans useful reagents for the identification of specific metal ions or the simultaneous determination of two ions. The wavelengths are much longer than those of the formazan anion (Table 14). The general trend for electron-rich substituents is toward a larger shift this is to be expected as it tends to enhance the aromatic character of the ring and increase the covalent character of the metal — nitrogen bond. The sharpness of the absorption band has been attributed to coordination to the heterocyclic nitrogen as in 232.57S...

Metal-Nitrogen Bond Lengths and Torsion Angles between the Metal and Nitrogen Coordination Planes for Three-Coordinate Aluminum, Gallium, Indium, and Thallium Amides... 

Numerous quantum mechanic calculations have been carried out to better understand the bonding of nitrogen oxide on transition metal surfaces. For instance, the group of Sautet et al have reported a comparative density-functional theory (DFT) study of the chemisorption and dissociation of NO molecules on the close-packed (111), the more open (100), and the stepped (511) surfaces of palladium and rhodium to estimate both energetics and kinetics of the reaction pathways [75], The structure sensitivity of the adsorption was found to correlate well with catalytic activity, as estimated from the calculated dissociation rate constants at 300 K. The latter were found to agree with numerous experimental observations, with (111) facets rather inactive towards NO dissociation and stepped surfaces far more active, and to follow the sequence Rh(100) > terraces in Rh(511) > steps in Rh(511) > steps in Pd(511) > Rh(lll) > Pd(100) > terraces in Pd (511) > Pd (111). The effect of the steps on activity was found to be clearly favorable on the Pd(511) surface but unfavorable on the Rh(511) surface, perhaps explaining the difference in activity between the two metals. The influence of... 

Insertion into metal nitrogen bonds is illustrated by the formation of the anion [(C6F5)2Pd(S2CNIIPh)] in the reaction of [Pd2(C6F5)4(p-NHPh)2]2-with carbon disulfide.362... 

Trends in metal-nitrogen bonding can be illustrated by series of nitrido (H3MN, M = W, Os) and imido (H3MNH, M = Ta, Re, Ir) complexes, isovalent counterparts... 

Many metal derivatives of nitrogenous systems containing one or more bonds linking nitrogen to a metal (usually, but not exclusively, a heavy metal) show explosive instability. Individually indexed compounds are ... 

Organohydrazine derivatives play an important role in the coordination chemistry of rhenium since they represent important intermediates in the preparation of nitrido, imido, or dinitrogen complexes as has been described in the previous sections. They are defined as complexes which possess metal-nitrogen-nitrogen bonds, which would (strictly applied) also include dinitrogen complexes, and indeed this class has attracted considerable attention in the exploration of biological nitrogen fixation. 

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