Polynitrogen Clusters Containing Five-Membered Rings

摘要

Possible structures of N_(15) 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 N_5 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 [N_(10) (D_(2d)),N_(12) (C_(2h)),N_(14) (C_(2h))],(c) containing one five-membered ring and a side-chain with an even number of total nitrogen atoms [N_8 (C_s),N_(10) (C_s),N_(12) (C_s),N_(14) (C_s)],(d) containing one five-membered ring and a side-chain with an odd number of total nitrogen atoms [N_(11) (C_s),N_(13) (C_s),N_(15) (C_s)],(e) chain clusters with an even number of total nitrogen atoms [N_8 (C_(2h)),N_(10) (C_(2h)),N_(12) (C_(2h)),N_(14) (2h)],and (f) chain clusters with an odd number of total nitrogen atoms [N_(11) (C_2,),N_(13) (C_(2v)),N_(15) (C_(2v))].For another series of clusters with two five-membered ring units [N_(11) (C_2),N_(13) (C_(2v)),and N_(15) (C_(2v))] (series b) the N_(13) (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).