从头算量子化学计算方法对高氯酸镁溶液中存在的离子缔合物种及缔合过程的研究

使用了量子化学计算方法在HF/6-31＋G*水平下对高氯酸镁溶液中的高氯酸根水合, 可能存在的离子缔合物种以及离子缔合过程进行了研究. 高氯酸根的第一水合层至少需要6个水分子才能填满, 在水合数6以下时, 每增加一个水分子可以造成v₁-频率1.7 cm^－1的蓝移. 高氯酸根与第一个无水镁离子结合可以造成较大的红移, 与第二个和第三个镁离子结合后, 可使v₁-频率连续的反向蓝移, 这种变化与镁离子的极化作用相关. 高氯酸根与水合镁离子可形成水合的缔合物种, 包括溶剂共享离子对、接触离子对、溶剂共享型三离子团簇和接触型三离子团簇, 其中溶剂共享型离子对和含有两个高氯酸根和一个镁离子的三离子团簇, 可对v₁-频率造成较小的蓝移, 与实验的拉曼光谱符合较好. 高氯酸镁在溶液浓度升高时发生的离子缔合过程被推测为: 自由水合离子→溶剂共享型离子对→含有两个高氯酸根的溶剂共享型三离子团簇→六水合高氯酸镁晶体, 这一过程与硫酸镁有较大不同而与硝酸镁接近.     

用从头算法研究高氯酸钠溶液中存在的离子缔合物种及缔合过程

采用量子化学计算方法在HF/6-31+G*水平下对高氯酸钠溶液中可能存在的离子缔合物种及浓度升高时溶液中发生的离子缔合过程进行了研究. 高氯酸根与水合钠离子可形成溶剂共享离子对、接触离子对、三离子及多离子团簇等离子缔合物种, 当体系中水比较充足时, 钠离子可以保持较规整的六配位八面体构型, 而当水分子比较少时, 则生成不规则的五配位构型. 以上水合离子缔合物种中的ν₁-ClO₄^-频率与水合硝酸根中的参比值相比, 分别发生4.7, 8.5及14~17 cm^-1的蓝移, 除以影响因子后, 其与实验结果符合得很好. 通过将计算结果与实验结果进行对比, 高氯酸钠溶液在浓度升高时发生离子缔合的过程可简略表示为“自由水合离子→溶剂共享型离子对→单齿接触离子对→阳-阴-阳型三离子团簇→链状多离子团簇→网状多离子团簇→无定形晶体”. 这个过程与硫酸镁相似, 而与硝酸镁、高氯酸镁和硝酸钠不同.     

金属离子Na+,Li+及Mg2+与C1O4-和NO3-形成的无水离子缔合物种的从头算量子化学研究

采用量子化学计算方法在B3 LYP/6-311++G**水平下对Na+,Li+和Mg2+与ClO4-和NO3-形成的离子缔合物种的结构以及v1-频率进行了研究,并将结果与SO42-和上述3种阳离子形成的物种进行了对比.在缔合物种结构方面,当阳离子数目≤2时,与SO42-体系相似,ClO4-和NO3-主要与阳离子形成双齿缔合结构,而当阳离子数目＞2时,特别是具有2个正电荷的Mg2+离子数目较多时,由于阳离子间的斥力更大,与阳离 子结合能力较弱的ClO4-和NO3-较难与其形成稳定的离子团簇,而在SO42-体系中,则易形成单齿缔合结构.在v1-频率的变化趋势方面,3种阴离子形成的缔合物种大体相同,说明无水离子团簇的频率变化主要受阳离子性质和缔合结构影响.虽然阴离子性质也有部分影响,但不占主要地位.     

高温及超临界条件下 MgCl2与CaCl2水溶液中离子水化与缔合的量子化学计算

对NaCl等碱金属水溶液的研究表明,室温条件下,离子在溶液中以水合形式存在,而在高温及超临界时,阴阳离子将结合成为离子对．采用量子化学计算,研究了MgCl2与CaCl2水溶液中水化与缔合的情况．通过Gaussian98软件包计算了阳离子的水化自由能以及离子对的生成能,从而获得水合离子与离子对的热力学稳定性及其随温度、压力的变化情况．通过比较热力学稳定性,考察了两种溶液中水化与缔合的变化情况．研究结果表明,MgCl2与CaCl2水溶液中离子水化与缔合的变化趋势与碱金属溶液基本一致,但是存在一个过渡区域,该区域内离子对与水合离子共存,因此需要采用不同于碱金属溶液的方法处理MgCl2与CaCl2水溶液．     

金属离子Na+ , Li+ , Mg2+与硫酸根离子形成的无水缔合物种的从头算量子化学研究

计算并讨论了Na+, Li+和Mg2+ 3种离子与SO42-离子形成离子缔合物的结构以及阳离子的结合对ν1-SO42-频率的影响. 结果表明, 在缔合物结构方面, 阳离子数目越少, 离子间斥力越小, 越容易形成阳离子与硫酸根间距离更短, 结合更紧密的双齿缔合结构; 而当阳离子数目增加时, 特别是当具有2个正电荷的Mg2+离子数目较多时, 离子间的斥力使多离子团簇不稳定, 易形成阳离子与硫酸根间距离更长的单齿缔合结构. 有2种阳离子作用可影响ν1-SO42-频率, 一种是极化作用, 可使ν1-SO42-频率红移; 另一种是成键作用, 可使ν1-SO42-频率蓝移. 当金属离子数目≤2时, 阳离子的极化作用占主导地位, 第一个阳离子能使ν1-SO42-频率发生红移, 而当阳离子数目增多时, 不同方向结合的其它阳离子可以削弱第一个阳离子的极化作用, 因此导致多离子团簇中ν1-SO42-频率红移的减小. 当阳离子数目≥3时, 极化作用影响减小, 成键作用占据主导地位, 导致ν1-SO42-频率更大蓝移的单齿缔合结构取代双齿结构, 并使多离子团簇中的ν1-SO42-频率继续发生蓝移.     

溶液相有机化合物pKa的量子化学计算

寻找一种理论计算方法来验证和补充实验数据,得到较为精确的溶剂化自由能和pK_a值,是众多理论化学家长期以来研究的重要方向。本综述较为详细地总结了近年发展起来的PCM理论模型在溶液相化合物溶剂化自由能、特别是近十年来有机化合物pK_a值的量子化学计算中的最新成果,比较了各种不同计算方法的精确性和各自特点。     

NaCl对疏水缔合聚合物溶液性质的影响研究

研究了NaCl对疏水缔合聚合物溶液性质的影响。结果表明,所合成的疏水缔合聚合物的特性粘数随NaCl浓度的增加而降低,其表观粘度则先降低后增加,继续增加NaCl浓度,溶液粘度降低,但仍保持很高的粘度。环境扫描电镜(ESEM)研究表明,疏水缔合聚合物在去离子水体系中会形成网状结构,而在NaCl浓度为5g·L-1的溶液中,ESEM照片显示疏水缔合聚合物的结构为致密的树枝状结构,且存在一临界缔合浓度。     

含氟疏水缔合聚丙烯酰胺的制备及溶液性质研究

以异佛尔酮二异氰酸酯(IPDI)、四氟丙醇(FOH)和烯丙基聚乙二醇(APEG1200)为原料合成了含氟表面活性单体(FSM),并以FSM为疏水单体,在它的胶束溶液中实现了其与丙烯酰胺(AM)和2-丙烯酰胺基-2-甲基丙磺酸(AMPS)的水溶液共聚合,制备出含氟疏水缔合聚丙烯酰胺(FAPAM)。采用流变仪研究了FAPAM水溶液的疏水缔合性能,并考察了盐、剪切率和温度对FAPAM缔合性能的影响。结果表明,FAPAM水溶液的疏水缔合性能受FSM含量的影响,具有一定的耐盐性。FAPAM属于假塑性体系,表现出较强的抗剪切性能。适当升高温度对FAPAM水溶液的疏水缔合有一定的促进作用。     

35Cl NMR研究溶液中离子对和离子缔合

测量了Sr和Ba高氯酸盐在乙腈和乙醇中0.5 mol·L~(-1)溶液的~(35)Cl NMR峰宽Δv和粘度η。按核四极矩弛豫机理, 结合文献中Mg~[1]和Ca~[2]盐的数据, 一种溶剂中各盐的Δv/η之比当反映~(35)Cl核处的电场梯度平方之比。按接触型离子对假设, ~(35)Cl处电场梯度平方之比应等于(r_++r_-)~(-6)。测得各盐的Δv/η之比与计算的(r_++r_-)~(-6)吻合, 论证了在乙腈与乙醇中为接触型离子对。同时文中报告了Δv/η和盐的摩尔电导随水或DMF加入的变化。     

混合增溶剂对离子缔合物作用的研究

慈云祥等在研究铂、钯、金-碘化钾-丁基罗丹明B显色体系时发现,使用明胶或阿拉伯胶与TritonX-100的混合液,有良好的增溶作用和极好的增敏效应。我们的研究表明:在不少离子缔合物显色体系中,聚乙烯醇-TritonX-100或阿拉伯胶-β-环糊精等混合液,也有很好的增溶(或分散)、增敏和增稳作用。     

Ab initio investigation on ion-associated species and association process in aqueous Na2SO4 and Na2SO4/MgSO4 solutions

In the present paper, the possible ion associated species in pure Na(2)SO(4) and mixed Na(2)SO(4)/MgSO(4) aqueous solutions are investigated via the ab initio method at the HF/6-31+G? level. The vibrational v(1)-SO(4)(2-) band is analyzed. For the unhydrated species, when the number of metal ions around the SO(4)(2-) ion is less than 3, the dominating effect to the v(1)-SO(4)(2-) band is the polarization of the cations, while the M-O bonding will be dominating as the number is equal to or more than 3. For the hydrated species, the coordinated structures of the Na(+) ion in all ion pairs are not stable due to the strong effect of the SO(4)(2-) ion but relatively stable in the triple ion (TI) clusters since there are fewer vacant hydration sites around the SO(4)(2-). The v(1)-SO(4)(2-) frequencies are close to that of the hydrated SO(4)(2-) ion in the ion pairs and larger in both Na(2)SO(4) and Na(2)SO(4)/MgSO(4) TI clusters. On the basis of our calculated results, the evolvement of Raman spectra in the Na(2)SO(4)/MgSO(4) droplet with the molar ratio of 1:1 is explained.     

Ab initio investigation on the ion‐associated species and process in Mg(NO3)2 solution

In the present article, two focal subjects, i.e., hydration of the NO and associated ion species in the Mg(NO₃)₂ solution are researched by using the ab initio method. Nitrate ions with the hydration number of 1–6 are optimized at the HF/6‐31+G* level. Their relative energies, binding energies, and v₁‐NO frequencies are also presented. The investigation of the binding energies shows the hydration number is 3–6 in the solvent abundant environment. The associated species, including ion pairings, triple‐ and multiple‐ion clusters, are also optimized at the same level and their v₁‐NO frequencies are calculated for comparing with the results in experiments. From the comparison, the new associated process via aqueous free ions → solvent‐shared ion pairings → solvent‐shared triple and multiple ion clusters → contact multiple ion clusters → amorphous crystal is proposed. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010     

Electrochemical behaviour of V2O5 xerogel in aqueous LiNO3 solution

By dissolving crystalline V₂O₅ in hydrogen peroxide and drying at elevated temperature, the V₂O₅ xerogel was obtained. Its electrochemical behaviour was examined in aqueous solution of LiNO₃ by both cyclic voltammetry and galvanostatic charging/discharging cycling. Peak-to-peak potential separation observed at the cyclovoltammograms indicated fast Li⁺ intercalation/deintercalation reactions. Initial discharge capacity amounted to 69 mAhg^?1, and after 100 charging/discharging cycles, capacity fade amounted to 11% only. This presents a remarkable improvement in comparison with the behaviour of crystalline, vanadium oxide based, lithium intercalates in aqueous electrolytes.     

Ab-initio studies on electroosmotic separation: separation of 1,4-dioxane in water solution

A novel technique in membrane separation based on the phenomenon of electroosmosis, recently developed by us [Jain et al., J. Membrane Sci., 78 (1993) 53] has been used to demonstrate the practicability of the phenomenon for the separation of 1,4-dioxane from a dioxane-water mixture. The method shows favourable prospects as a membrane separation process, at least for the separation of close boiling mixtures, provided that the components of the mixture possess a large difference in their dielectric constant values. The analysis of the data indicates that the separation of dioxane increases as the dioxane concentration in the feed solution increases. It is also found that the separation of dioxane increases as the applied electrical potential difference across the membrane increases.     

Electrochemical Oxidation of Tantalum in LiNO3-NaNO3-KNO3 Melt

Growth kinetics of anodic oxide films on tantalum in a molten eutectic mixture of lithium, sodium, and potassium nitrates was studied and the influence exerted by introduction of hydroxide and chromate ions into the nitrate mixture was considered. The basic kinetic parameters of anodic oxidation of tantalum under galvanostatic conditions were determined.     

Ab-initio study of OCCS,OCCS+ and related species

Calculations on OCCS and OCCS⁺ are reported at the G1, G2, G2(MP2) and CCSD(T) levels of theory. Optimised geometric parameters, ionisation potentials, enthalpies of formation and dissociation energies have been calculated. The results are compared with those for OCCO and SCCS species. CCSD(T)/aug-cc-pvtz energies give better agreement with experimental energies than do the G2 energies. The calculated ionisation potential of OCCO suggests that the (CO)₂ species observed experimentally is not OCCO.     

铝电极在LiNO3-KNO3熔盐中的电化学行为

采用循环伏安和恒电位电解法考察了铝电极在LiNO3-KNO3熔盐中的电化学行为. 实验结果表明, 在该熔盐中, 锂离子在铝电极上的电还原过程伴随着新生态的锂原子向电极内部的随后扩散步骤; 锂原子进入铝电极后与铝发生合金化, 形成β-LiAl合金和γ-LiAl合金; 锂离子在铝电极上的还原过程受还原态锂在铝基体内的扩散步骤控制. 循环伏安实验发现, 铝电极在该熔盐中的氧化和还原峰电流都先随循环次数增加而增大, 最后基本上趋于稳定. 这表明铝电极在该熔盐体系中具有较好的电化学稳定性.     

Ab-initio Investigation on Ion-associated Species and Association Process in NaNO3 Solution

<正>Some ion-associated species existed possibly in NaNO_3 solution were investigated via the ab-initio method. The hydrated ion parings,triple and multiple ion clusters in NaNO_3 solution are all analogous to those in Mg(NO_3)_2 system except that the bi-dentate structures can not be formed.Only one solvent-shared ion paring has larger v_1-NO_3~- frequency than the hydrated NO_3~- ion.And all triple clusters with two hydrated Na~+ ions and one NO_3~- have larger v_1-NO_3~- frequency than the hydrated NO_3~- ion.The ion association process in NaNO_3 solution is predicted as free ions→solvent-separated ion pairings→solvent-shared ion pairings→solvent-shared triple ion clusters→contact triple ion clusters→contact multiple ion clusters→amorphous NaNO_3,which is not analogous to that in MgSO_4 but those in Mg(NO_3)_2 and Mg(ClO_4)_2 systems.     

Neutron Diffraction Study on the Structure of Aqueous LiNO3 Solutions

Neutron diffraction measurements were carried out at 25 °C for aqueous LiNO₃ heavy water solutions, (*LiNO₃) _x (D₂O)_1?x where x = 0.1, 0.05 and 0.01, in which the ⁶Li/⁷Li isotopic ratios were varied. Structural information on intermolecular nearest neighbor Li⁺···D₂O interactions in the extensive concentration range was derived from the first-order difference function, ?_Li(Q), obtained from the difference in scattering cross sections between ⁶Li- and ⁷Li-enriched sample solutions. The nearest neighbor Li⁺···O distance and coordination number for sample solution with x = 0.1 were determined to be r _LiO = 1.969 (8) Å and n _LiO = 4.12 (6), respectively, corresponding to the four-coordinated Li⁺ ion in the solution. On the other hand, those obtained for the solution with x = 0.01 are r _LiO = 2.00 (2) Å and n _LiO = 6.0 (2), respectively, indicating that hexaaqua Li⁺ is dominant in the dilute solution. These results clearly indicate that a concentration dependence of the hydration number of Li⁺ occurs in the aqueous solutions.     

LiNO3/N,N-二甲基甲酰胺溶液光谱性质的研究和模拟

利用红外光谱和量子化学计算方法研究了LiNO3/N,N-二甲基甲酰胺(DMF)溶液中离子溶剂化和离子缔合现象,得出了阳离子和阴离子在溶液中的存在形式以及DMF分子间自身的内部结构,并对(DMF)n结构进行了优化及热力学性质计算.在此基础上,提出阳离子进入溶剂化层的机理是,DMF分子之间相互作用形成不同形式的(DMF)n...