杂多阴离子[GeMo_(12)O_(40)]^(4-)α/β异构体的密度泛函研究

DFT study of the α/β-[GeMo_(12)O_(40)]^(4-) heteropolyanion

采用密度泛函方法,在DND基组水平上,对[GeMo12O40]4-杂多阴离子最常见的α和β异构体进行了几何构型优化,得到了与X射线晶体衍射实验结果相一致的结构参数,并在此基础上进行了振动频率分析,得到了杂多阴离子的电子结构、热力学特性和振动光谱,通过定义α,β异构体异构化反应的Gibbs函变ΔGα-β与温度的关系,研究了这两种异构体的相对稳定性.结果表明:低温时α异构体更稳定,高温时β异构体更稳定些,550K左右为转变点.振动频率分析得到2种异构体的最强峰位于4个频率位置,分别指认为aνs(Mo—Od),aνs(Mo—Od),aνs(Mo—Oc—Mo),aνs(Ge—Oa),aνs(Mo—Ob—Mo)振动,与红外光谱(IR)的特征振动峰相对应,观察到了特征频率的振动模式,从理论计算角度说明了RocchiccioliDeltcheff关于振动模式的设想是合理的.

Based on the density functional theory at DND basis set level,the structure of α/β-[GeMo_(12)O_(40)]^(4-) which is coincide with that of X-ray diffraction data(average),has been optimized.Frequency analysis was carried out on the basis of optimized structure,and electron structure,thermodynamic properties and vibration spectra were obtained.By define a isomerizational reaction Gibbs free energy(ΔG_(α-β))of α/β-[GeMo_(12)O_(40)]^(4-) isomerize reaction,we study the relative stability of those two isomer.The results show that α-isomer is more stable at lower temperature,however,β-isomer is more stable at higher temperature,and the transition temperature is 550 K.Four vibration frequency sites are assigned to ν_(as)(Mo—O_(d)),ν_(as)(Mo—O_(d)),ν_(as)(Mo—O_(c)—Mo),ν_(as)(Ge—O_(a)),(ν_(as)(Mo—O_(b)—Mo))respectly.We also study the normal model of characteristic frequencies and the results approve Rocchiccioli-Deltcheff's assumptions.