Monitoring the Activation of Open Metal Sites in [Fe x M3- x(μ3-O)] Cluster-Based Metal-Organic Frameworks by Single-Crystal X-ray Diffraction

Wenmiao Chen; Zhi Wang; Qi Wang; Khaoula El-Yanboui; Kui Tan; Heather M Barkholtz; Di-Jia Liu; Peiyu Cai; Liang Feng; Youcong Li; Jun-Sheng Qin; Shuai Yuan; Di Sun; Hong-Cai Zhou

doi:10.1021/jacs.2c13299

Monitoring the Activation of Open Metal Sites in [Fe _x M_{3- x}(μ₃-O)] Cluster-Based Metal-Organic Frameworks by Single-Crystal X-ray Diffraction

J Am Chem Soc. 2023 Mar 1;145(8):4736-4745. doi: 10.1021/jacs.2c13299. Epub 2023 Feb 15.

Authors

Wenmiao Chen^{1

2}, Zhi Wang³, Qi Wang², Khaoula El-Yanboui⁴, Kui Tan⁴, Heather M Barkholtz⁵, Di-Jia Liu⁵, Peiyu Cai², Liang Feng², Youcong Li¹, Jun-Sheng Qin², Shuai Yuan^{1

2}, Di Sun³, Hong-Cai Zhou^{2

6}

Affiliations

¹ State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, P. R. China.
² Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255, United States.
³ School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, P. R. China.
⁴ Department of Materials Science & Engineering, University of Texas at Dallas, Richardson, Texas 75080, United States.
⁵ Chemical Sciences & Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States.
⁶ Department of Materials Science and Engineering, Texas A&M University, College Station, Texas 77842, United States.

Abstract

While trinuclear [Fe_xM_3-x(μ₃-O)] cluster-based metal-organic frameworks (MOFs) have found wide applications in gas storage and catalysis, it is still challenging to identify the structure of open metal sites obtained through proper activations and understand their influence on the adsorption and catalytic properties. Herein, we use in situ variable-temperature single-crystal X-ray diffraction to monitor the structural evolution of [Fe_xM_3-x(μ₃-O)]-based MOFs (PCN-250, M = Ni²⁺, Co²⁺, Zn²⁺, Mg²⁺) upon thermal activation and provide the snapshots of metal sites at different temperatures. The exposure of open Fe³⁺ sites was observed along with the transformation of Fe³⁺ coordination geometries from octahedron to square pyramid. Furthermore, the effect of divalent metals in heterometallic PCN-250 was studied for the purpose of reducing the activation temperature and increasing the number of open metal sites. The metal site structures were corroborated by X-ray absorption and infrared spectroscopy. These results will not only guide the pretreatment of [Fe_xM_3-x(μ₃-O)]-based MOFs but also corroborate spectral and computational studies on these materials.