Probing Acidity in Metal–Organic Frameworks via Pyridine Adsorption

Semilocal density functional theory (DFT) and semiemprical
GFN1/GFN2-xTB,
as well as selected DFTB/3ob calculations, were performed to examine
acidity in metal–organic frameworks (MOFs) using pyridine (Py)
as a probe molecule. We studied Py adsorption on both Lewis and Bro̷nsted
acid sites in ten distinct MOF structures. Our study provides detailed
insight into their structures, thermodynamic properties, and vibrational
spectra in selected ranges. All geometrical and energetic parameters
obtained at the GFN1/GFN2-xTB levels were compared with those calculated
using DFT. The results suggest that GFN1-xTB can only be used as a
low-cost substitute for DFT for some systems. The adsorption energy
prediction usually leads to unsatisfactory findings. GFN2-xTB and
DFTB/3ob perform better than GFN1-xTB. Importantly, we identified
areas where the GFN1/GFN2-xTB methods could be improved to yield more
accurate results. By analyzing the density overlap region indicator
(DORI) versus the adsorption energies, we revealed the nature and
type of interactions in Py@MOFs.

本研究采用半局域密度泛函理论（DFT）、半经验GFN1/GFN2-xTB方法，以及选定的DFTB/3ob计算方案，以吡啶（Py）为探针分子，对金属有机框架（MOFs）中的酸性特征展开探究。我们针对十种不同MOF结构中的路易斯（Lewis）与布朗斯特（Brønsted）酸位点上的吡啶吸附行为进行了系统研究。本工作详细剖析了选定范围内的体系结构、热力学性质与振动光谱。将GFN1/GFN2-xTB级别下获取的所有几何与能量参数与DFT计算结果进行了对比分析。结果表明，GFN1-xTB仅可作为部分体系下DFT的低成本替代方案，其吸附能预测结果往往难以令人满意。GFN2-xTB与DFTB/3ob的表现优于GFN1-xTB。尤为关键的是，我们明确了GFN1/GFN2-xTB方法可优化的方向，以获得更为精准的计算结果。通过分析密度重叠区域指示器（DORI）与吸附能的关联关系，我们揭示了Py@MOFs中相互作用的本质与类型。