图4. B3LYP/6-31g水平下理论计算优化的脱水状态(a, c, e)及再吸水状态(b, d, f)的ASAs结构^[6]；(g)通过¹⁷O{¹H, ²⁷Al} PRESTO-TRAPDOR实验及对得到的¹⁷O{²⁷Al} TRAPDOR曲线进行模拟，确定ASAs中Al-OH的键长用以区分Al^V-BAS的结构，如酸性桥式羟基（黑色曲线，O-Al键长为2 Å）或酸性伪桥式硅羟基（灰色区域，O-Al键长为3~4.4 Å）^[41]，“?60 ppm”和“15 ppm”为¹⁷O NMR信号

Fig.4. Optimized structure of Al^V species in dehydrated states (a, c and e) and in corresponding rehydrated states (b, d, and f), both calculated at B3LYP/6-31g theoretical level^[6]; (g) ¹⁷O{²⁷Al} TRAPDOR curves obtained from ¹⁷O{¹H, ²⁷Al} PRESTO-TRAPDOR experiment were simulated to determine the Al-OH distance, for discriminating the structure of Al^V-BASs, corresponding to bridging silanols (black line, O-Al distance of 2 Å) and pseudo-bridging silanols (gray shaded area, O-Al distance range of 3 to 4.4 Å)^[41], the corresponding ¹⁷O chemical shifts were at -60 and 15 ppm