Jose Reshma, Kancharlapalli Srinivasu, Ghanty Tapan K, Pal Sourav, Rajaraman Gopalan
Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, 400076, India.
Theoretical Chemistry Section, Bhabha Atomic Research Centre, Mumbai, 400085, India.
Chemistry. 2022 Mar 28;28(18):e202104526. doi: 10.1002/chem.202104526. Epub 2022 Feb 19.
The coordinatively unsaturated chromium(II)-based Cr [(Cr Cl) (BTT) ] (Cr-BTT; BTT =1,3,5-benzenetristetrazolate) metal-organic framework (MOF) has been shown to exhibit exceptional selectivity towards adsorption of O over N /H . Using periodic density functional theory (DFT) calculations, we attempted to decipher the origin of this puzzling selectivity. By computing and analyzing the magnetic exchange coupling, binding energies, the partial density of states (pDOS), and adsorption isotherms for the pristine and gas-bound MOFs [(Cr (X) Cl) (BTT) ] (X=O , N , and H ), we unequivocally established the role of spin states and spin coupling in controlling the gas selectivity. The computed geometries and gas adsorption isotherms are consistent with the earlier experiments. The binding of O to the MOF follows an electron-transfer mechanism resulting in a Cr superoxo species (O ) with a very strong antiferromagnetic coupling between the two centers, whereas N /H are found to weakly interact with the metal center and hence only slightly perturb the associated coupling constants. Although the gas-bound and unbound MOFs have an S=0 ground state (GS), the nature of spin the configurations and the associated magnetic exchanges are dramatically different. The binding energy and the number of oxygen molecules that can favorably bind to the Cr center were found to vary with respect to the spin state, with a significant energy margin (47.6 kJ mol ). This study offers a hitherto unknown strategy of using spin state/spin couplings to control gas adsorption selectivity in MOFs.
基于配位不饱和铬（II）的金属有机框架材料Cr [(Cr Cl) (BTT) ]（Cr-BTT；BTT = 1,3,5-苯三唑）已被证明对O的吸附相对于N /H具有卓越的选择性。利用周期性密度泛函理论（DFT）计算，我们试图解读这种令人费解的选择性的起源。通过计算和分析原始的和气体结合的金属有机框架材料[(Cr (X) Cl) (BTT) ]（X = O 、N 、H ）的磁交换耦合、结合能、态密度（pDOS）和吸附等温线，我们明确确定了自旋态和自旋耦合在控制气体选择性方面的作用。计算得到的几何结构和气体吸附等温线与早期实验结果一致。O与金属有机框架材料的结合遵循电子转移机制，形成一种Cr超氧物种（O ），两个中心之间具有非常强的反铁磁耦合，而N /H与金属中心的相互作用较弱，因此仅略微扰动相关的耦合常数。尽管气体结合的和未结合的金属有机框架材料具有S = 0的基态（GS），但自旋构型的性质和相关的磁交换却有显著差异。发现结合能和能够有利地结合到Cr中心的氧分子数量随自旋态而变化，具有显著的能量差（47.6 kJ mol ）。这项研究提供了一种迄今未知的策略，即利用自旋态/自旋耦合来控制金属有机框架材料中的气体吸附选择性。
