Polynitrogen clusters containing five-membered rings

Possible structures of N₁₅ cluster were examined by ab initio (MP2) and density functional theory (DFT) methods with the 6-31G* basis set. Their stabilities were compared together with other polynitrogen clusters N_n (n = 8, 10–14) reported in the literature. The order of stability was made respectively according to even or odd numbers of the total nitrogen atoms in clusters. It is found that both for even-numbered clusters N_2n (n = 4–7) and odd-numbered clusters N_{2n + 1} (n = 5–7) the thermodynamically most stable isomers are all based on pentazole units; for each one of N_n (n = 8, 10–15) clusters, the more conjugated the five-membered ring the more stable is the isomer; and, the more side-chains the N₅ ring links the less stable is the isomer. Another finding is that the larger the cluster the less stable is the cluster for every series of clusters of (a) containing two five-membered rings with an even number of total nitrogen atoms N₁₀ (D_2d), N₁₂ (C_2h), N₁₄ (C_2h)], (c) containing one five-membered ring and a side-chain with an even number of total nitrogen atoms N₈ (C_S), N₁₀ (C_S), N₁₂ (C_S), N₁₄ (C_S)], (d) containing one five-membered ring and a side-chain with an odd number of total nitrogen atoms N₁₁ (C_S), N₁₃ (C_S), N₁₅ (C_S)], (e) chain clusters with an even number of total nitrogen atoms N₈ (C_2h), N₁₀ (C_2h), N₁₂ (C_2h), N₁₄ (C_2h)], and (f) chain clusters with an odd number of total nitrogen atoms N₁₁ (C_2v), N₁₃ (C_2v), N₁₅ (C_2v)]. For another series of clusters with two five-membered ring units N₁₁ (C₂), N₁₃ (C_2v), and N₁₅ (C_2v)] (series b) the N₁₃ (C_2v) shows the best stability. It is also found that the even-numbered nitrogen clusters are more stable than the odd-numbered ones in comparison of series (a) with (b), (c) with (d), and (e) with (f). © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004