Polynitrogen cyclic

The nomenclature,particularly of complex compounds, is not always satisfactory in spite of the good work of the nomenclature commissions of the International Union of Pure and Applied Chemistry. Occasionally, a competent chemist would, not be able to write the correct structure based on a given name. This is particularly noticeable in the naming of open chain and cyclic polynitrogen compounds... 

Analysis suggested that cyclic delocalization could, however, occur in 17 and 18 to a lesser extent than in pyrrole and benzene, respectively [97], This suggests low aromaticity of 17 and 18. Donation from sp lone pairs (Scheme 9) weakens the N-N sp -sp ) single bonds in the cyclic conjugated hydronitrogens and polynitrogens. 

The pentazolate anion. Ns (11.2), is estimated to have a half-life of 2.2 days, whereas that of the parent pentazole HN5 is predicted to be only ca 10 min in methanol at 0 Although HN5 is unknown, the cyclic anion N5 has been detected by tandem mass spectrometric studies of 4-hydroxyphenylpentazole. Similarly to its congener P5 (Section 11.2), N5 (isoelectronic with cyclopenta-dienide [C5H5] ) has the potential to form metallocene-like complexes. The acyclic (V-shaped) cation Ns has been isolated as a hexafluoroantimonate salt, which decomposes at ca 70 °C. The estimated energy density of [N5] [N5] is approximately twice that of hydrazine, a well-known rocket propellant, suggesting that this ionic polynitrogen allotrope would be an excellent monopropellant... 

In contrast to the few reports of attempts to synthesize polynitrogens, there are himdreds of computational papers on these species. Fortunately, a fraction of these will suffice to give a fair perspective on om theoretical understanding of these (almost all experimentally imknown) compoimds. We will first report on some sitrveys of a variety of polynitrogens, then look in some detail at a few of those of particttlar irrterest, considering cyclic and then acyclic molecules. 

There are varied examples of polynitrogen bases that form bidentate cyclic structures with metal cations. The most clear-cut cases of such chelate effects are encountered with polyamines, among which ethylenediamine is the best-studied case. The main studies, concerning the cations of Li, Na, K, Mg, A1 and Cu, are cited in ref. [54], The combined spectroscopic and ab initio study of copper complexes shows bidentate cyclic structures for the four iV-methyl-substituted derivatives of ethylenediamine, but a hydrogen bond stabilized monodentate sUiicture for the Cu+/ethylenediamine is also possible [54],... 

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