The double hydroxide of Li+ and Al3+ is an anionic clay comprising positively charged metal hydroxide layers and intercalated anions. While the structure of the iono-covalently bonded metal hydroxide layer is well known, relatively less knowledge is available regarding the manner in which the anions and water molecules are packed in the interlayer region. The sulfate ion is of special interest as it can potentially intercalate in a multiplicity of orientations and grow an extended hydration sphere. The sulfate-intercalated double hydroxide was synthesized by the imbibition of Li2SO4 into both the gibbsite and bayerite forms of Al(OH)3 to obtain layered double hydroxides with the nominal formula Li2Al4(OH)12SO4·nH2O (n = 4–8). The as-prepared compounds were poorly ordered and did not yield any structural information. Temperature-induced partial dehydration yielded ordered phases of different structures in the two systems. Simulation of the powder patterns of different model structures, followed by structure refinement in both direct and reciprocal spaces, showed that the gibbsite-derived phase yielded a two-layer polytype of hexagonal symmetry (space group P63/m). The local symmetry of the sulfate ion was close to D2d with one of the C2 axes of the SO42− being nearly parallel to the c axis of the crystal. The bayerite-derived phase yielded a one-layer polytype of monoclinic symmetry (space group C2/m). The sulfate ion was oriented with its C3 axes tilted away from the stacking direction. Cooling and rehydration (relative humidity ~70%) resulted in a reversible expansion of the basal spacing due to the ingress of water molecules from the ambient humidity into the interlayer region. Hydration in both cases resulted in turbostratic disorder. The disorder in the bayerite-derived phase was a result of random intergrowth of motifs with rhombohedral and monoclinic symmetries.

中文翻译：

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水合对锂铝硫酸盐插层层状双氢氧化物多型和无序的影响

Li+ 和Al3+ 的双氢氧化物是一种阴离子粘土，包含带正电荷的金属氢氧化物层和嵌入的阴离子。虽然离子共价键合的金属氢氧化物层的结构是众所周知的，但关于阴离子和水分子在层间区域的堆积方式的知识相对较少。硫酸根离子特别令人感兴趣，因为它可以潜在地嵌入多个方向并形成扩展的水合球。插入硫酸盐的双氢氧化物是通过将 Li2SO4 吸入三水铝石和三羟铝石形式的 Al(OH)3 来合成的，以获得标称式为 Li2Al4(OH)12SO4·nH2O (n = 4–8) 的层状双氢氧化物。所制备的化合物排序不佳，没有产生任何结构信息。温度诱导的部分脱水在两个系统中产生不同结构的有序相。模拟不同模型结构的粉末图案，然后在直接和倒易空间中进行结构细化，表明三水铝石衍生相产生了六边形对称的两层多型（空间群 P63/m）。硫酸根离子的局部对称性接近 D2d，其中 SO42− 的 C2 轴之一几乎平行于晶体的 c 轴。三羟铝石衍生相产生单斜对称的单层多型（空间群 C2/m）。硫酸根离子的 C3 轴偏离堆积方向。由于水分子从环境湿度进入层间区域，冷却和再水化（相对湿度~70%）导致基底间距的可逆膨胀。两种情况下的水合作用都导致了湍流障碍。三羟铝石衍生相的无序是具有菱面体和单斜对称性的基序随机共生的结果。