轻稀土离子水合物Re^(3+)(H_(2)O)_(n)(n=1~12,Re=La、Ce、Pr、Nd)的DFT研究

DFT study on light rare earth ion hydrate Re^(3+)(H_(2)O)_(n)(n=1−12,Re=La,Ce,Pr,Nd)

采用Material studio的DMol3模块研究了La^(3+)、Ce^(3+)、Pr^(3+)、Nd^(3+)四种离子的水合物Re^(3+)(H_(2)O)_(n)(n=1~12),分析了几何优化后的构型的几何结构、结合能、前线轨道、电荷、振动情况。结果表明:La^(3+)、Ce^(3+)、Pr^(3+)、Nd^(3+)四种轻稀土离子第一水化层的最小水合数分别为4、6、7、7;在相同水合数条件下,Re—O的平均键长大小顺序为La>Ce>Pr>Nd,Re^(3+)(H_(2)O)_(10)的Re—O平均键长约为2.6Å,轻稀土离子水合物的水化层半径约为3.22~3.59Å。轻稀土离子的水化反应为放热反应,当水分子配位数相同时,结合能大小顺序为La>Ce>Pr>Nd。电荷分析结果显示,水合反应过程中稀土离子得到电子,当第一水化层填满后,Re^(3+)(H_(2)O)_(n)性质逐渐趋于稳定,Re离子的电荷量在2e左右。前线轨道分析结果显示,不同于离子半径的变化,四种稀土离子自身的硬度大小顺序为La>Nd>P>Ce。模拟的La^(3+)(H_(2)O)_(n)的红外光谱显示,随着水分子数量的增加,V_(sym)和V_(asym)峰发生蓝移;当n大于10时,V_(sym)和V_(asym)峰不再发生蓝移,说明第一水化层外的水分子没有与La离子发生反应。

DMol3 module of Material Studio was used to study the hydrate Re^(3+)(H_(2)O)_(n)(n=1−12)of four kinds of light rare earth ion coordination water quantities of La,Ce,Pr and Nd.The geometric structure,binding energy,frontier molecular orbital,charge and vibration of the geometrically optimized configuration were analyzed.The results show that the minimum hydration number of the first hydration layer of La^(3+),Ce^(3+),Pr^(3+)and Nd^(3+)are 4,6,7 and 7,respectively,which can contain up to 10 water molecules.The order of average Re—O bond length is La>Ce>Pr>Nd,the average Re—O bond length of Re^(3+)(H_(2)O)_(10) is about 2.6Å,and the hydration layer width of light rare earth ionic hydrate is about 3.22−3.59Å.The hydration reaction of light rare earth ions is exothermic.When the coordination number of water molecules is the same,the order of binding energy is La>Ce>Pr>Nd.Charge analysis results show that rare earth ions gain electrons in the hydration reaction.When the first hydration layer is filled,the properties of Re^(3+)(H_(2)O)_(n) gradually become stable,and the charge of Re ions is around 2e.The results of frontier molecular orbital analysis show that,different from the change of ion radius,the hardness sequence of the four rare earth ions is La>Nd>Pr>Ce.The simulated infrared spectra of La^(3+)(H_(2)O)_(n) reveal that,with the increase of the number of water molecules,the V_(sym) and V_(asym) peaks show blue shift.When n is greater than 10,the V_(sym) and V_(asym) peaks show no blue shift,indicating that the water molecules outside the first hydration layer will not react with La ions.