Molecular nitrogen ligands

Silver(I) complexes with macrocyclic nitrogen ligands are also very numerous. Mono- or homodi-nuclear silver-containing molecular clefts can be synthesized from the cyclocondensation of functionalized alkanediamines or triamines with 2,6-diacetylpyridine, pyridine-2,6-dicarbalde-hyde, thiophene-2,5-dicarbaldehyde, furan-2,5-dicarbaldehyde, or pyrrole-2,5-dicarbaldehyde in the presence of silver(I).486 97 The clefts are derived from bibracchial tetraimine Schiff base macrocycles and have been used, via transmetallation reactions, to complex other metal centers. The incorporation of a range of functionalized triamines has provided the conformational flexibility to vary the homodinuclear intermetallic separation from ca. 3 A to an excess of 6 A, and also to incorporate anions as intermetallic spacers. Some examples of the silver(I) complexes obtained are shown in Figure 5. 

Formally, the lone pairs on molecular nitrogen, hydrogen cyanide, and carbon monoxide are sp hybrid orbitals, whereas NLMO hybridizations calculated even lower p contributions. Hence, these lone pairs have low directionality, the electron density remains close to the coordinating atom and interaction between the lone pair and the Be2+ is comparatively weak. The Be-L bonds are easily disrupted and ligand exchange consequently can proceed with a low activation barrier. A high degree of p character, on the other hand, means that the lone pair is directed toward beryllium, with electron density close to the metal center, and thus well suited for coordination. 

Photoreduction of ammine complexes containing aliphatic amines instead of ammonia does not lead to production of molecular nitrogen instead, a variety of other ligand oxidation products are formed. Moeller and co-workers have studied three such systems in 3M HC1 solution 58 59 rather similar results have been obtained in more dilute acid solutions.55... 

Ceruloplasmin is the major copper-containing protein in mammalian blood plasma (see Section 62.1.8.5), and appears to consist of a single polypeptide chain of molecular weight 130 000.1341 The nine-line superhyperfine splitting in the ESR spectrum of the type 2 copper has been interpreted in terms of four equivalent nitrogen ligands.978... 

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