Nitrogen on metals

The chemisorption and reactivity of the oxides of nitrogen on metal surfaces are of great environmental interest because of their connection to the reaction with carbon monoxide, leading to innocuous products, e.g. 

Cyanides are made by action of carbon and nitrogen on metallic oxides. For example, barium cyanide is made by heating a mixture of barium oxide and carbon to a red heat in a stream of nitrogen ... 

Fig. 62. Apparatus for absorbing nitrogen on metallic calcium or magnesium.

Adsorbed nitrogen on metal films is desorbed by increasing the temperature at a constant rate. This gives TPD spectra or thermal desorption spectra, and the adsorbed states were analyzed on W, Fe, Mo or Re. Three peaks of adsorbed... 

We consider first some experimental observations. In general, the initial heats of adsorption on metals tend to follow a common pattern, similar for such common adsorbates as hydrogen, nitrogen, ammonia, carbon monoxide, and ethylene. The usual order of decreasing Q values is Ta > W > Cr > Fe > Ni > Rh > Cu > Au a traditional illustration may be found in Refs. 81, 84, and 165. It appears, first, that transition metals are the most active ones in chemisorption and, second, that the activity correlates with the percent of d character in the metallic bond. What appears to be involved is the ability of a metal to use d orbitals in forming an adsorption bond. An old but still illustrative example is shown in Fig. XVIII-17, for the case of ethylene hydrogenation. 

Studies on metal-pyrazole complexes in solution are few. The enthalpy and entropy of association of Co(II), Ni(II), Cu(II) and Zn(II) with pyrazole in aqueous solution have been determined by direct calorimetry (81MI40406). The nature of the nitrogen atom, pyridinic or pyrrolic, involved in the coordination with the metal cannot be determined from the available thermodynamic data. However, other experiments in solution (Section 4.04.1.3.3(i)) prove conclusively that only the N-2 atom has coordinating capabilities. 

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). 

Quantum calculations on metal-assisted tautomerization indicate a substantial stabilization to protonation of the endocyclic nitrogen atoms (99). In the case of HgCHg, adducts are formed by binding at either A-N6 or C-N4, which increases the stability of the respective N1H+ or N3H+ protonated species by 10-14 kcal/mol. For Pt11 binding at C-N4 the effect is much greater at 30-34 kcal/mol. 

The nitrogen on ruthenium work is consistent with the observation made on the H/Cl/Au Eley-Rideal chemistry and, taken together, the implications of these two pieces of work are quite profound, suggesting that an accurate theory of surface reactions cannot be constructed without accounting for strong coupling between the reaction coordinate and the metals electron... 

Pyrophoric in air, deflagrates under nitrogen on scratching with a metal spatula, and reacts explosively with alcohols or water. 

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