碱土金属叠氮化合物(CaN_6)_n(n=1～5)团簇结构与性质的密度泛函理论研究

Density Functional Theory Study on the Structure and Properties of Alkaline-earth Metal Azides (CaN_6)_n (n=1～5) Clusters

利用密度泛函理论在B3LYP/6-311G*水平上对碱土金属叠氮化合物(CaN6)n(n=1～5)团簇各种可能构型进行了几何优化,预测了各团簇的最稳定结构.并对最稳定结构的成键特性、电荷分布、振动特性及稳定性进行理论研究.结果表明,叠氮化合物中叠氮基以直线型存在,CaN6团簇的最稳定结构为线型结构,(CaN6)n(n=2～5)团簇首先由两个叠氮基与两个Ca原子构成一个近似菱形,再由菱形相互垂直形成链状最稳定结构;叠氮基中间的N原子显示正电性,两端的N原子显示负电性,且与Ca直接作用的N原子负电性更强,金属Ca原子和N原子之间形成很强的离子键;(CaN6)n(n=1～5)团簇最稳定结构的IR光谱分为4个部分,其最强振动峰均位于2195～2280cm-1,振动模式为叠氮基中N—N键的反对称伸缩振动;稳定性分析显示,(CaN6)3和(CaN6)5团簇相对于其他团簇较为稳定.

Possible geometrical structures and relative stability of alkaline-earth metal azides （CaN6）n （n= 1～5） clusters are studied by using the hybrid density functional theory （B3LYP） with 6-311G＊ basis sets. For the most stable isomers of （CaN6）n （n=1～5） clusters, the bond properties, charge distributions, vibrational properties, and stability are analyzed. The calculated results show that azido in azides has linear structure, the most optimized CaN6 has linear structure, and the most optimized （CaN6）n （n=2～5） clusters have chain structure of perpendicularity of approximate diamond composed by two azido with two Ca atoms. The middle N atoms of azido show positive, the N atoms at both ends of azido show negative, and the N atoms effected with Ca atoms directly show more negative. There is strong ionic bond between the Ca and N atoms. The IR spectra of the most optimized （CaN6）n （n=1～5） clusters have four vibrational sections, the whole strongest vibrational peak lies in 2195～2280 cm-1, and the vibrational mode is anti-symmetric stretching vibration of N—N bonds in azido. Stability analysis show that （CaN6）3 and （CaN6）5 clusters are more stable than other clusters.