Sipos Pál, Hefter Glenn, May Peter M
Chemistry-DSE, Murdoch University, Murdoch, WA 6150, Australia; Department of Inorganic and Analytical Chemistry, University of Szeged, Szeged H-6701, PO Box 440, Hungary.
Talanta. 2006 Nov 15;70(4):761-5. doi: 10.1016/j.talanta.2006.02.008. Epub 2006 Mar 13.
(27)Al NMR and Raman spectra of alkaline aluminate solutions with 0.005M</=Al(III)</=3M in various M'OH solutions (M'(+)=Na(+), K(+) and Li(+)) were recorded and analysed. Caustic concentrations up to 20M were used to explore whether higher aluminium hydroxo complexes are formed at extremely high concentrations of hydroxide. A single peak was observed on the (27)Al NMR spectrum of each solution. The chemical shift of this peak shifts significantly upfield with increasing M'OH in solutions with Al(III)<0.8M. This variation shows a strong dependence on the cation of the solution and practically disappears in systems with Al(III)>/=0.8M. For Raman spectra of solutions with Al(III)=0.8M and NaOH>/=10M, the peak maximum of the symmetric nu(1)-AlO(4) stretching of Al(OH)(4)(-) shifted progressively from approximately 620 to approximately 625cm(-1) and decreased in intensity with increasing NaOH. In parallel, modes centred at approximately 720 and approximately 555cm(-1) (cf. approximately 705 and approximately 535cm(-1) at lower NaOH, ascribed to a dimeric aluminate species appeared, and their intensities increased with increasing NaOH. These variations in the (27)Al NMR and Raman spectra can be interpreted in terms of contact ion-pairs formed between the cation of the medium and the well-established Al(OH)(4)(-) or the dimeric aluminate species. Assumption of higher aluminium hydroxo complex species (e.g., Al(OH)(6)(3-)) is not necessary to explain the spectroscopic effects observed.
记录并分析了在各种M'OH溶液（M'(+)=Na(+)、K(+)和Li(+)）中，Al(III)为0.005M≤Al(III)≤3M的碱性铝酸盐溶液的²⁷Al NMR和拉曼光谱。使用高达20M的苛性碱浓度来探究在极高浓度的氢氧化物下是否会形成更高的铝羟基络合物。在每种溶液的²⁷Al NMR光谱上观察到一个单峰。在Al(III)<0.8M的溶液中，随着M'OH的增加，该峰的化学位移显著向高场移动。这种变化对溶液中的阳离子有很强的依赖性，并且在Al(III)≥0.8M的体系中实际上消失。对于Al(III)=0.8M且NaOH≥10M的溶液的拉曼光谱，Al(OH)₄⁻的对称ν₁ - AlO₄伸缩振动的峰最大值从约620cm⁻¹逐渐移至约625cm⁻¹，并随着NaOH的增加而强度降低。同时，以约720cm⁻¹和约555cm⁻¹为中心的模式（相比之下，在较低NaOH时约为705cm⁻¹和约535cm⁻¹，归因于二聚铝酸盐物种）出现，并且它们的强度随着NaOH的增加而增加。²⁷Al NMR和拉曼光谱中的这些变化可以用介质阳离子与已确定的Al(OH)₄⁻或二聚铝酸盐物种之间形成的接触离子对来解释。不需要假设更高的铝羟基络合物物种（例如，Al(OH)₆³⁻）来解释观察到的光谱效应。
