论(Cl_2BN_3)_n(n=1-4)簇合物

用密度泛函论B3LYP/6-311+G*法,计算(C1_2BN_3)_n(n=1-4)簇合物的结构和性质.发现,多聚体(C1_2BN_3)_n(n=2-4)的优化构型原来是由不同子体系的叠氮基α-N和B原子相连而形成的环状结构。几何参数的比较分析还发现N_α-B、N_α-N_β、N_β-N_Υ和B-Cl的键长与聚合度密切相关,环状构型中B-N_α-B键角总比N_α-B-N_α大。同时计算所有优化构型的振动频率,将其IR谱归类.通过热力学计算,发现簇合物的稳定性为3A>3B;4A>4B.由焓变可知,从单体形成二聚体于热力学不利,而形成最稳定三聚体和四聚体的温度分别达800K和500K仍是有利的.

Studies on (Cl_2BN_3)_n(n=1-4) clusters

Density functional theory (DFT) has been employed to study the structures and properties of (Cl_2BN_3)_n(n=1-4) clusters at the B3LYP/6-311+G* level. The optimized clusters (Cl_2BN_3)_n (n=2-4) all possess cyclic structure formed by B atoms bridged by the α-nitrogen of the azide groups. Comparisons of the structural parameters reveal that the N_α-B, N_α-N_β, N_β-N_γ and B-Cl bond lengths are closely related with oligomerization degree n, B-N_α-B angles in the cyclic oligomers are consistently larger than the N_α-B-N_α ones. Frequency calculations are carried out on each optimized structure, and their IR spectra are assigned. Thermodynamic properties demonstrate that the stabilities of the clusters decreases in the order 3A>3B; 4A>4B. The dimerization is thermodynamically unfavorable by the enthalpy. Formations of the more stable (Cl_2BN_3)_3 trimer and (Cl_2BN_3)_4 tetramer species are thermodynamically favorable in the gas phase at temperatures up to 800 K and 500 K, respectively.