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.     

从头算量子化学计算方法对硝酸锂溶液中存在的离子缔合物种及缔合过程的研究

利用量子化学计算方法,在HF/6-31+G*水平下对硝酸锂溶液中可能存在的离子缔合物种,以及当浓度升高时溶液中发生的离子缔合过程进行了研究.硝酸根与水合锂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,在所有的缔合物种中,锂离子大都以形成四配位四面体结构为主,只有少数情况下存在能量较高的五配位结构.以上3种水合离子缔合物种中的v1(NO3-)频率与水合硝酸根中的参比值相比,分别发生1.4,-6.9以及大于2.8 cm-1的蓝移,考虑到实验光谱中v1(NO3-)带是持续蓝移的.推测的硝酸锂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→阳-阴-阳型三离子团簇→链状多离子团簇→网状多离子团簇→晶体".这个过程与在硝酸镁和硝酸钠中的缔合过程是相似的.     

高氯酸锂甲醇溶液中离子溶剂化和离子缔合现象

通过红外光谱技术探讨了高氯酸锂甲醇溶液中离子与溶剂、离子与离子之间的相互作用。红外光谱分析结果表明:锂离子与溶剂发生了相互作用导致甲醇分子的O-H伸缩振动区蓝移,ClO4-的特征谱带的变化表明了溶液中存在离子缔合。根据密度泛函理论,对不同溶剂化数的配合物结构和两种离子对形式进行优化及热力学性质的计算。     

乙烯醇钠的从头算研究(英文)

在ＲＨＦ／３－２１Ｇ和ＲＨＦ／６－３１＋Ｇ水平上优化了乙烯醇钠的的平衡构型及过渡态，比较了不同构型的稳定性。在ＲＨＦ／６－３１＋Ｇ水平上探讨了气相中由乙醛和氢氧化钠生成乙烯醇钠的机理。并在ＭＰ２（ｆｕｌ）／６－３１＋Ｇ／／ＭＰ２（ｆｕｌ）／６－３１＋Ｇ水平下计算了反应热     

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.     

缬氨酸热分解机理的从头算研究

用量子化学从头算方法在RHF/6-21G水平上全优化计算了缬氨酸及其热分解中间产物、产物分子的几何构型,得到其总能量和Mulliken集居数等数据。通过对计算结果的分析,提出了缬氨酸的热分解反应机理。     

电化学石英晶体微天平研究高氯酸钠水溶液中活性炭电极的离子存储行为

以电化学石英晶体微天平(EQCM)为主要测试手段,在不同浓度的高氯酸钠(NaClO4)水溶液中研究了水合离子吸附到活性炭电极孔隙过程中电极的质量变化.对于每种电解液,根据Raman光谱和EQCM数据分别计算了本体溶液中和电极/溶液界面上Na+的水合数.通过比对这两组Na+水合数,探讨了Na+存储到活性炭负极过程中的去溶剂化效应.     

甲醛与甲酰胺相互作用的从头算研究

The optimizations geometries and vibrational frequencies of H2CO,HCONH2 and acquired 3 complexes between H2CO?HCONH2 have been calculated by using the ab initio method at the MP2/6-31G（ d）and MP2 （FC）/6-311++G（d,p）level. The non-minimum structures with negative vibrational frequencies are excluded. The lowest energy conformer of these complexes is a cyclic structure with N - H?O and C - H?O hydrogen bonds in a common plane. No significant changes are observed in the geometries of the monomers in their complexed state. The most characteristic geometrical properties of the complex are the lengthening of the contacting N-H bonds by 0.4-1.1 pm,and the general shortening of the contacting C-H bonds by 0.3-0.4 pm with respect to the monomers. The interaction energies of complexes have been corrected by the basis set superposition error （BSSE）using the full Boys-Bernardi counterpoise correction scheme. The corrected complex interaction energies of 3 structures at MP2/6-311++G（2df,3p）/ / MP2（FC）/6-311++G（d,p）level are -29.94, -16.10 and -18.45 kJ/mol,respectively. The interaction energies indicate that C - H?O is a weak hydrogen bond. The results of natural bond orbital population analysis reveals that there is only a small charge-transfer in the process of forming the complexes. The results of natural bond orbital analysis and atom in the molecule scheme appear quite significant in view of their importance for understanding the mechanisms of intermolecular interaction leading to hydrogen bonding. The results of molecular interaction energy decomposition analysis show that the electrostatic interaction plays an essential role in stabilizing the H2CO?HCONH2 complexes.     

HNNH3的从头计算研究

Ab-Initio studies applying the 3-21G, 6-31G and 6-31G** basis sets and also including the MP2 correction were carried out on H2NNH2, HNNH3 and the transition state molecule of the reaction H2NNH2=HNNH3. First, the geometry of the three molecules was optimized using the theoretical methods mentioned in the Hartree-Fock(HF) scheme. The energies of the molecules corresponding to RHF/6-31 G** geometries were subsequently calculated including electron correlation effects at the level of the second-order Moller-Plesset(MP2) perturbation theory. The vibrational frequencies, net charges and dipole moments were obtained from the theoretical calculations. The results of our ab-initio calculations indicate unambiguously that H2NNH2 is thermodynamically more stable than HNNH3. On the other hand, an isolated HNNH3 molecule once created would be rather stable since barriers for its unimolecular isomerization and decomposition are relatively high. Nevertheless, HNNH3 can be considered as an intermediate in chemical processes involving N2H4. This assumption has been supported by further calculation at higher level of theory.     

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.     

用光度法测定物种溶液状态的缔合数和缔合度

以分光光度法研究物种的溶液状态,提出了新的模型测定缔合数和缔合度并使之定量化。经过联吡啶和罗丹明6G体系验证,表明该方法准确可靠。     

Ab initio Investigation on Unhydrated Ion-associated Species Between Na+, Li+, Mg2+ and SO2-4 Ions

计算并讨论了Na+,Li+和Mg2+3种离子与SO2-4离子形成离子缔合物的结构以及阳离子的结合对v1-SO2-4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v1 -SO2-4频率,一种是极化作用,可使v1-SO2-4频率红移;另一种是成键作用,可使v1 -SO2-4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v1-SO2-4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v1-SO2-4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v1 -SO2-4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v1-SO2-4频率继续发生蓝移.     

Ab-initio study on the stability,electronic and mechanical properties of transition metal nitrides under external pressure

Structures of transition metal nitrides (TMNs) were optimized using the plane-wave pseudopotential method based on density functional theory. Energy as a function of volume curves were calculated to predict the phase transition pressures. Density of states (DOS), charge density difference, and charge transfers were calculated. The elastic constant (C₁₁) and modulus (G) as a function of pressure were computed. Results showed that TMNs in the WC structure was most stable at normal pressure. All TMNs exhibited metallic, covalent and ionic property. Metallic character increased and covalent property reduced with increasing atomic number of TM atom. The elastic constant (C₁₁) and modulus (G) increased linearly with increasing pressure due to stronger hybridization, bonding and covalent property. Thus, mechanical property enhanced under external pressure.     

十一烯酸钠与十一酸钠水溶液的表面化学

决定表面活性剂性能的首要因素是其分子结构．关于表面活性剂性能随极性头类型、疏水基化学组成、疏水链数目、长度及分支等因素的影响已有许多研究[1]．相比之下，疏水基中含有双键的影响研究较少．实际上，在由两亲分子组成的生物膜中，不饱和脂肪酸酯的存在有重要意义，它使     

Solvent effects on complexation of crown ethers with LiClO4, NaClO4 and KClO4 in methanol and acetonitrile

The thermodynamic formation constants K_f for complexation of Li⁺, Na⁺ and K⁺ with the crown ethers 12C4 and 15C5 have been determined in methanol and acetonitrile at 25°C using precision conductivity data. The method permits evaluation of very small K_f values (e.g., K_f=6.98 mol^–1-dm³ for LiClO₄+12C4 in methanol) as well as fairly large values (e.g., K_f=2.73×10⁴ mol^–1-dm³ for NaClO₄+15C5 in acetonitrile). The determination of K_f values from conductivity data takes into consideration the often neglected ion pair formation of both the uncomplexed and the complexed cations. Our results for K_f are generally consistent with previously reported values based on potentiometry, calorimetry and polarography, but there are significant differences in several cases which we attribute to neglect of ion association both for the uncomplexed or free cation K_a and the macrocyclic complexed cation K_a2. Our results are also consistent with the well known concepts relating the magnitude of K_f to both the cavity diameter and ion-solvent interactions. Limiting molar conductivities ₂ ⁰ for the complex salt (M-crown ether) (ClO₄) in both solvents were generally found to be smaller or very close to the corresponding quantity ₁ ⁰ for the binary MClO₄-solvent system. However, in methanol, single ion limiting molar conductivities for the cationic complexes ₂ ⁰ exhibit anomalous behavior which is attributed to solvation differences between free cations and complexed cations.     

Effect of the diffuse double layer on the interpretation of EQCM results in dilute NaClO4 solutions

The response of the electrochemical quartz crystal microbalance (EQCM) in dilute NaClO₄ solutions was studied with gold and iron electrodes during a stepwise increase of the perchlorate concentration. In the range from 10⁻⁴ M to 7.8×10⁻² M, the quartz resonant frequency of the 10 MHz AT cut crystals increased by about 700 Hz, indicating a mass loss on the electrode. A model was developed in which the diffuse double layer and the oscillating bulk electrolyte layer, characterised by the velocity decay length of the damped shear wave in solution, are treated as two independent, superimposed sheets. By assuming a characteristic thickness of the diffuse double layer according to the Gouy–Chapman theory and by treating the diffuse double layer as a rigid sheet, the measured mass loss could be simulated qualitatively. The viscosity changes in the diffuse double layer as well as in the sensed electrolyte bulk layer were found to be negligible in the concentration range investigated. In dilute solutions, the frequency shift following a concentration change is entirely due to thinning of the diffuse double layer with increasing concentration. The results demonstrate the importance of diffuse double layer effects for EQCM measurements in dilute electrolytes.