碱土金属叠氮化合物(MgN_6)_n(n=1～5)团簇结构与性质的密度泛函理论研究

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(MgN6)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,MgN6团簇最稳定结构为直线型;(MgN6)2团簇最稳定结构为Mg2N2四元环平面结构;(MgN6)n(n=3～5)团簇最稳定结构是由2个叠氮基与2个Mg原子首先构成近似菱形,再由近似菱形延伸形成的链状结构。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Mg直接作用的N原子负电性更强,金属Mg原子和N原子之间形成很强的离子键。(MgN6)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2209～2313cm-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,(MgN6)3和(MgN6)5团簇相对于其他团簇较为稳定。

Density Functional Theory Study on the Structure and Properties of Alkaline-Earth Metal Azides (MgN6)n (n=1~5) Clusters

Possible geometrical structures and relative stability of Alkaline-earth metal azides (MgN₆)_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 (MgN₆)_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, most of the optimized MgN₆ has linear structure, most of the optimized (MgN₆)₂ has plane structure of Mg₂N₂ ring, and most of the optimized (MgN₆)_n(n=3~5) have chain structure of perpendicularity of approximate diamond. The middle N atoms of azido show negative, the N atoms at both ends of azido show positive, and the N atoms effected with Mg atoms directly show more negative. Between the Mg atoms and N atoms exist a strong ionic bond. The IR spectra of the most optimized (MgN₆)_n(n=1~5) clusters have four vibrational sections, the whole strongest vibrational peak lies in 2 209~2 313 cm^-1, and the vibrational mode is anti-symmetric stretching vibration of N-N bonds in azido. Stability analysis shows that (MgN₆)₃ and (MgN₆)₅ clusters relative to other clusters are more stable.