FT-Raman spectroscopic evidences for the preferential solvation of sodium tetrafluorobrate in acetonitrile-based mixed solvents

Solutions of sodium tetrafluorobrate in acetonitrile-dimethylformamide, and acetonitrile-dimethylsulfoxide mixtures have been studied by FT-Raman spectroscopy for three solvent compositions, respectively. New bands due to solvent molecules in the first solvation shell of Na(+) were detected in the region of the O=C--N deformation and CH(3) rocking mode for amide and of the S=O and C--S stretching modes for sulfoxide. The individual solvation numbers of sodium cation in different environment were deduced. In all the cases, it is found that the sodium ion was preferentially solvated by DMF or DMSO in respective binary solvents. This result was further supported by ab initio calculations.     

Study of the interactions of sodium thiocyanate, potassium thiocyanate and ammonium thiocyanate in water+N,N-dimethylformamide mixtures by Raman spectroscopy

Raman spectra of water+N,N-dimethylformamide (DMF) mixtures and their solutions with NaNCS, KNCS and NH(4)NCS were obtained. The bands of nu(CO) stretching, delta(OCN) bending, r(CH(3)) rocking and nu(N-CH)(3)) stretching of the DMF molecule with and without salts were studied. The dependence of the vibration frequencies and Raman intensities of the bands on the composition of the mixed solvent was discussed. The change of the band frequencies as a result of the presence of the salts and the solvation of the cations by the solvent molecules was examined. The stronger cation solvation by the aprotic solvent molecules instead of the water molecules in DMF concentrated solutions was discussed. The nu(CN) and nu(CS) vibrations of the SCN(-) ions were observed as a function of the cation present and the solvent composition. The presence of the SCN(-) ions as "free", contact ion pairs, or solvent separated pairs, was discussed.     

Individual solvation numbers around the nickel(II) ion in an N,N-dimethylformamide and N,N-dimethylacetamide mixture determined by Raman spectrophotometry.

Individual solvation numbers around the nickel(II) ion have been determined by titration Raman spectroscopy in N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) mixtures at 298 K. The in-plane bending vibration (delta(O=C-N)) of DMF and the stretching vibration (v(N-CH3)) of DMA were used in the present analysis. These Raman bands of solvent molecules shift to higher frequencies upon coordination of the solvent molecules to the metal ion. By analyzing the band intensities of free and bound solvent molecules with increasing concentration of the metal ion, the solvation number around the metal ion can be evaluated. Because the individual solvation numbers of DMF and DMA around the nickel(II) ion in the mixture are determined independently, the total solvation number is obtained as their sum. It was found that the total solvation number remains 6 in all mixtures of the DMA mole fraction x = 0 - 1. Although DMF and DMA have practically the same electron-pair donor capacities, the nickel(II) ion prefers DMF to DMA, and an equal solvation number is attained at x = 0.75. This is ascribed to the solvation steric effect of DMA.     

Real structure of formamide entrapped by AOT nonaqueous reverse micelles: FT-IR and 1H NMR studies

Noninvasive techniques such as FT-IR and (1)H NMR spectroscopy have been employed to investigate the solubilization of formamide, FA, and its aqueous solution, FA-water, by sodium 1,4-bis(2-ethylhexyl)sulfosuccinate, AOT, in heptane or isooctane reverse micelles, respectively. Partially deuterated FA (FADH) was used in the FT-IR experiments and nu(OD), n(ND) were analyzed. Also, the nu(C=O) band of FA was investigated. For AOT, the changes of the SO(3)(-) group's symmetric, nu(s), and asymmetric, nu(a), bands were also studied. The results are showing that FA is interacting strongly with the Na+ counterions of the surfactant through electrostatic interactions maintaining their hydrogen bond network present in the FA bulk. Accordingly, partially deuterated FA is "frozen" inside the aggregates and it is possible to detect, by FT-IR technique, the cis and trans isomers. Curve fitting of the nu(OD) (in the FA-water mixture) band requires use of two peaks because the band is asymmetric, not because the solubilizate molecules are present in layers of different structure. The chemical shifts of the (1)H bound to N and C of FA were studied by (1)H NMR. The comparison of the chemical shift of AOT in reverse micelles with FA and the FA-water mixture in the polar core of the aggregate shows that there is a strong preferential solvation of Na+ by FA (through electrostatic interaction) and the AOT's sulfonate group by water (through hydrogen bond interaction).     

Characterization of metal ions in coordinating solvent mixtures by means of Raman spectroscopy.

Titration Raman spectroscopy has been developed for studying the solvation structure of metal ions in solution. The method affords us the solvation number, and the value thus obtained in neat solvents is in good agreement with that determined by EXAFS. The method is then applied to solvent mixtures, and the individual solvation number for each solvent is extracted. In a solvent mixture of N,N-dimethylformamide (DMF) and N,N,N',N'-tetramethylurea (TMU), the metal ion prefers DMF to TMU, which is ascribed to the solvation steric effect. The same applies also for the solvent mixture of N,N-dimethylpropionamide (DMPA) and DMF. However, unlike TMU, DMPA changes its conformation from the planar cis to non-planar staggered upon solvation to the metal ion. The enthalpy for the conformational change of DMPA is positive in the bulk, while it is significantly negative in the coordination sphere of the manganese(II) ion. Here, we briefly describe the procedure of measurements and analyses for the titration Raman spectroscopy, and review the solvation structure of the alkaline earth, first transition metal(II) and lanthanide(III) ions in some solvent mixtures in view of solvation steric effect.     

NaNO3和NaClO4在N,N-二甲基甲酰胺中的离子溶剂化

利用红外光谱研究了NaNO₃和NaClO₄在N,N-二甲基甲酰胺(DMF)溶剂中发生离子-溶剂和离子-离子的相互作用, 分析结果表明, DMF的OC-N谱带发生了明显的变化. 定量计算了在Na⁺浓度为0.22~1.24 mol/kg范围内的溶剂化数为1~4. 对谱图中酰胺基上C-N和CO的特征峰强度随Na⁺浓度变化的对比, 推测离子溶剂化作用导致DMF的酰胺基内部形成共轭键. 利用量子化学方法进行优化及热力学性质计算, 得到C-N键伸缩振动频率及红外光谱强度变化规律. 优化结构与实验结论相符合. 由NaNO₃的ν₂谱带及NaClO₄的ν₁谱带的解析得到溶液中阴离子缔合效应的一般规律, 并通过阴离子缔合特征峰与酰胺基上的N-C-N面外振动峰(865 cm^-1)的变化情况, 讨论了溶液中的离子溶剂化作用.     

NaCl-NaBr系熔盐溶液的分子动力学研究

近年来，用计算机模拟馆公的结构和性质的研究已有较大进展[1，2]．但研究工作多集中在有阴离子相同、阳离子不同的盐组成的“同阴离子系”（commonanionsystems），而对由阳离子相同、阴离子不同的盐组成的“同阳离子系”（commoncationsystems）熔盐溶液则甚少研究．鉴于自然界和生产中同阳离子系也不乏实例，建立同阳离子系熔盐溶液的理论屯有必要．为止匕我们先选择NaCI－NaBr系熔盐溶液（同阳离子系的一个最简单的典型）为对象，开展分子动力学方法计算机模拟研究．1模型和计算方法采用标准文献中的计算模拟和方法，离子间劳用Fumi-…     

共聚焦拉曼光谱研究过饱和硝酸铵液滴中NH4+, NO3- 和H2O之间的相互作用

将硝酸铵液滴沉积在石英基底上,通过降低该液滴周围环境的相对湿度,测定了该液滴由低浓度直至过饱和状态下高信噪比的拉曼光谱.其中,相对湿度的变化可以精确控制液滴浓度的改变.在相对湿度(RH)由72.1%降低至37.9%的过程中,硝酸铵液滴v1-NO-3峰位保持在1048cm-1,半峰宽为10cm-1.该现象表明NO-3周围的水分子被NH4+取代后不会对v1-NO-3造成影响,说明水分子和NH4+所形成的氢键具有相同的强度.对2500-4000cm-1范围内的拉曼光谱进行成分分析,2890、3090、3140、3220、3402及3507cm-1分别被指认为NH+4伞状弯曲振动的泛频、NH+4伞状弯曲振动与摇摆振动的组合谱带、NH+4的对称伸缩振动、NH+4的反对称伸缩振动、水峰中强氢键成分和弱氢键成分.从拟合结果得出:强氢键在氢键结构中所占百分含量随液滴相对湿度的降低而减少,弱氢键所占百分含量随液滴相对湿度的降低而增加.该变化趋势是NO-3和NH+4之间复杂相互作用的结果.     

Nuclear magnetic relaxation and ionic solvation of23Na+ and81Br− in aqueous mixtures of simple amides

Ion-solvent interactions of Na⁺ and Br^– in binary aqueous mixtures of formamide,N-methylformamide (NMF), andN,N-dimethylformamide (DMF) are studied by use of²³Na and⁸¹Br magnetic relaxation times, extrapolated to zero salt concentration. The relaxation times, which are controlled by quadrupolar interaction, have been measured over the complete mixture range and are compared with a simplified theoretical formula. It turned out that the²³Na⁺ relaxation in H₂O-formamide and H₂O-NMF mixtures is in excellent agreement with theoretical predictions, implying nonpreferential solvation of Na⁺ in these systems. Small deviations of experimental from theoretical results in H₂O+DMF possibly indicate weak selective hydration of the cation. In the case of the anionic nuclei⁸¹Br^–, deviations from the theoretical curve occur which are to be expected, especially for systems where hydrophobic effects play a role. On the other hand, it is demonstrated that these deviations can easily be explained within the electrostatic theory by differences in structural details of the anionic solvation sphere in the mixtures compared to the pure solvents.     

Oxygen-hydrogen stretching frequencies for water and methanol in the primary solvent shells of cations and anions

Since the band for OH stretching of HOD molecules solvating perchlorate ions is clearly resolved, the remaining band can be analysed to give values for the OH absorption for the cation solvation shell: these are closely correlated with NMR shift data.     

丁二酸钠气溶胶液滴吸湿性的分子谱学研究

采用共聚焦拉曼光谱和傅里叶变换红外-衰减全反射(FTIR-ATR)技术, 研究了丁二酸钠气溶胶液滴的风化和潮解过程. 研究发现, 随着水质摩尔比的降低, 1420 cm-1处νs(COO-)的半峰宽由35 cm-1增加至42 cm-1, 表明过饱和丁二酸钠液滴内部Na+与丁二酸根存在弱相互作用; 过饱和丁二酸钠液滴风化形成亚稳态无水晶体, 而不是形成热力学更稳定的六水合晶体.     

FTIR studies of PVC/PMMA blend based polymer electrolytes

The polymer electrolytes composing of the blend of polyvinyl chloride-polymethyl methacrylate (PVC/PMMA) with lithium triflate (LiCF3SO3) as salt, ethylene carbonate (EC) and dibutyl phthalate (DBP) as plasticizers and silica (SiO2) as the composite filler were prepared. FTIR studies confirm the complexation between PVC/PMMA blends. The CCl stretching mode at 834 cm-1 for pure PVC is shifted to 847 cm-1 in PVC-PMMA-LiCF3SO3 system. This suggests that there is interaction between Cl in PVC with Li+ ion from LiCF3SO3. The band due to OCH3 at 1150 cm-1 for PVC-PMMA blend is shifted to 1168 cm-1 in PVC-PMMA-LiCF3SO3 system. This shift is expected to be due to the interaction between Li+ ion and the oxygen atom in PMMA. The symmetric vibration band and the asymmetric vibration band of LiCF3SO3 at 1033 and 1256 cm-1 shifted to 1075 and 1286 cm-1 in the DBP-EC plasticized PVC-PMMA-LiCF3SO3 complexes. The interaction between Li+ ions and SiO2 will lead to an increase in the number of free plasticizers (which does not interact with Li+ ions). When the silica content increases from 2% to 5%, the intensity of the peak at 896 cm-1 (due to the ring breathing vibration of free EC) increases in PVC-PMMA-LiCF3SO3-DBP-EC system.     

Distorted five-fold coordination of Cu2+(aq) from a Car-Parrinello molecular dynamics simulation

The solvation shell structure and dynamics of a single Cu2+ ion in a periodic box with 32 water molecules under ambient conditions has been investigated using Car-Parrinello molecular dynamics simulations in a time-window of 18 ps. Five-fold coordination with four equidistant equatorial water molecules at 2.00 A and one axial water molecule at 2.45 A from the Cu2+ ion is found. A "hole" without water molecules is found on the opposite side of the axial water. The ion-water bonding character for the equatorial water molecules is different from that of the axial water molecules, as shown by a localized orbital analysis of the electronic structure. Moreover, the calculated OD stretching vibrational band for the equatorial water molecules lies ca. 175 cm-1 below the axial-water band, in good agreement with experimental data. The equatorial-water band lies below, and the axial-water band above, the pure liquid D2O band, also in agreement with experimental data.     

Cyclohexane as a Li+ selective ionophore

The M+[cyclohexane][Ar] (M = Li, Na, and K) cluster ions were investigated using infrared photodissociation spectroscopy in the C-H stretching region. The alkali metal cation binds to the cyclohexane ring above the ring on the S6 axis via eta3 coordination. The C-H stretching modes are perturbed due to binding of the metal cation and display a significant spread in frequency. The shifts are greatest for the Li+ and decrease for Na+ and K+ with increasing ionic radius. It has been observed that cyclohexane displays greater selectivity for Li+ over Na+ than the cyclic ether, 12-crown-4. The charge transfer interaction between Li+ and cyclohexane is believed to be responsible for the selectivity of Li+ over other alkali metal ions.     

Solvation of Cr3+ cation in water-acetonitrile mixture studied by IR spectroscopy: molecular penetration into the solvation shells

Infrared spectra of mixtures of water and deuteroacetonitrile containing the Cr3+ cation have been studied as a function of concentration, time and temperature. The CN stretching vibration of CD3CN molecules has been used as a probe of the structural environments. The CN band in the spectra of the solutions is a superposition of four subbands, which may be attributed to CD3CN bound in the first, second, and third solvation shells of the cation and to non-bound CD3CN. The character of changes of the integral intensities of the subbands with time for various H2O:Cr3+ molar ratios are explained by suggesting mechanisms of molecular replacement within the solvation shells of Cr3+.     

ZnHZSM-5上丙烷芳构化的研究-丙烷的活化

研究了HZSM－5、ZnHZSM－5和ZnNaZSM－5上的羟基振动光谱和一氧化碳吸附的红外光谱，以及丙烷的芳构化反应．红外光谱中发现表征强B酸的3610cm－1羟基振动峰相对强度由于锌离子的引入和浸渍氢氧化钠而减小，说明了锌离子和钠离子均进入了分子筛的阳离子位；一氧化碳在锌离子上的吸附峰位在2232cm－1，说明进入阳离子位的锌离子是一种强L酸．反应结果表明，锌离子的引入大大地促进了丙烷的转化和芳烃选择性的提高；在一定范围内，随浸渍氢氧化钠量的增加，丙烷转化率下降，而丙烯的选择性和产率增加，说明了锌组份直接参与了丙烷的脱氢过程．Zn－L酸是丙烷活化脱氢的中心，丙烷在该中心上异裂活化直接脱氢．     

Lewis acid-base adducts: a quantitative Raman analysis of formamide and dimethylsulfoxide mixtures

Raman spectra of pure liquid dimethylsulfoxide (DMSO) and of binary mixtures of formamide (FA) and DMSO in different compositions were obtained. The vibrations involving the SO functional group in the band envelope at ca. 1050 cm(-1) of pure liquid DMSO are assigned to monomers, dimers and higher aggregates of DMSO. The appearance of a new band at 1024 cm(-1), whose intensity shows large dependence on the FA concentration, is assigned to a FA-DMSO adduct. This has been possible due to the two H-bond donor sites of FA and the strong donor character of DMSO that become the environment propitious for the donor-acceptor reaction. Quantitative analysis performed in the SO stretching region in the binary mixtures gives a 1:1 stoichiometry in this adduct in the limit of infinite dilution. This proportion is in full agreement with our previous determination for the FA-ACN adduct. The experimental evidence of the 1:1 FA-DMSO adduct is presented for the first time using Raman spectroscopy. The results described here open new possibilities to study the acid-base reactions nature of FA adducts.     

Infrared photodissociation spectroscopy of protonated acetylene and its clusters

The protonated acetylene cation, C2H3+, (also known as the vinyl cation) and the proton-bound acetylene dimer cation (C4H5+) are produced by a pulsed supersonic nozzle/pulsed electrical discharge cluster source. The parent ions are also generated with weakly attached argon "tag" atoms, e.g., C2H3+Ar and C4H5+Ar. These ions are mass selected in a specially designed reflectron time-of-flight mass spectrometer and studied with infrared laser photodissociation spectroscopy in the 800-3600 cm-1 region. Vibrational resonances are detected for both ions in the C-H stretching region. C2H3+ has a strong vibrational resonance near 2200 cm-1 assigned to the bridged proton stretch of the nonclassical ion, while C4H5+ has no such free-proton vibration. Instead, C4H5+ has resonances near 1300 cm-1, consistent with a symmetrically shared proton in a di-bridged structure. Although the shared proton structure is not the lowest energy isomer of C4H5+, this species is apparently stabilized under the supersonic beam conditions. Larger clusters containing additional acetylene units are also investigated via the elimination of acetylene. These species have new IR bands indicating that rearrangement reactions have taken place to produce core C4H5+ ions with the methyl cyclopropane cation structure and/or the protonated cyclobutadiene isomer. Ab initio (MP2) calculations provide structures and predicted spectra consistent with all of these experiments.     

Multiple charging of poly(propylene glycol) by binary mixtures of cations in electrospray

Single, double and triple charging of poly(propylene glycol) (PPG) (Mn = 1900 g/mol) in the presence of binary mixtures of cations (Li+, Na+, K+, Cs+, and NH4+) under electrospray ionization (ESI) conditions were investigated. For these studies, sodium ion was selected as the reference cation, and the resulting ion-intensities were evaluated as a function of the [Na+]/[C+] ratio (where C+ is the other cation, i.e., Li+, K+, Cs+ and NH4+). A linear relationship was found between INa+/IC+)and [Na+]/[C+] (INa+ and IC+ stand for the intensity of the singly charged PPG molecules cationized with Na+ and C+ ions, respectively). The slope of the INa+/IC+--[Na+]/[C+] plot (alpha) indicates the binding selectivity of Na+ ions to PPG chains with respect to cation C+. In the case of the doubly charged PPG chains, the INaNa2+/INaC2+ and INaC2+/ICC2+ versus [Na+]/[C+] ratio also yield straight lines with slopes of approximately alpha/2 and 2alpha, respectively (INaNa2+, INaC2+ and ICC2+ are the intensity of the doubly charged PPG chains cationized with two Na+ ions, Na+ and C+ ions, and two C+ ions, respectively). Similarly, linear dependences with the [Na+]/[C+] ratio for the corresponding intensity ratios of the triply charged PPG were found. Based on the value of alpha, the selectivity of the cations was found to increase in the order of Li+ < Cs+ approximately Na+ < K+ approximately NH4+. The observed relative ion intensities are interpreted on the basis of the solution state equilibrium between PPG and the cations. In addition, the investigations showed that the abundances of the doubly and triply charged PPG-containing mixed cations can be optimized in a simple way using the value of alpha.     

Identification of the rosasite group minerals--an application of near infrared spectroscopy

The ability of near infrared reflectance spectroscopy to classify the rosasite group minerals from spectral characteristics is demonstrated. NIR spectroscopy can be regarded as an alternative tool for structure analysis. The spectra show that rosasite group minerals with different cations can be distinguished. Ni2+ in nullaginite [Ni2(CO3)(OH)2] is conspicuous through a single broad band absorption feature at 8525 cm-1, extended from 11,000 to 7000 cm-1. The effect of Ni on Cu is seen in the spectrum of glaukosphaerite [(Cu, Ni)2(CO3)(OH)2] both by a red shift of the spectrum and reduction in intensity of bands with variable positions of band maxima for Cu2+ at 6995 cm-1 and Ni2+ at 7865 cm-1. The spectrum of rosasite [(Cu, Zn)2(CO)3(OH)2] is characterised by Cu2+ band at 7535 cm-1. Kolwezite [(Cu, Co)2(CO)3(OH)2] is a spectral mixture of Cu and Co but optically separated by Co2+ and Cu2+ peaks at 8385 and 7520 cm-1. Vibrational spectra of carbonates show a number of bands in the 7000-4000 cm-1 region attributable to overtones, combination of OH stretching and deformation modes. They appear to be uniform in nature since the structure of rosasite group minerals is identical. The complexity of these features varies between samples because of the variation in composition and hence is useful for discriminating different hydrous carbonates.