American Chemical Society
cm400858d_si_013.txt (441.77 kB)

Quantification of Site-Specific Cation Exchange in Metal–Organic Frameworks Using Multi-Wavelength Anomalous X‑ray Dispersion

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posted on 2016-02-19, 01:16 authored by Carl K. Brozek, Anthony F. Cozzolino, Simon J. Teat, Yu-Sheng Chen, Mircea Dincă
We employed multiwavelength anomalous X-ray dispersion to determine the relative cation occupation at two crystallographically distinct metal sites in Fe2+-, Cu2+-, and Zn2+-exchanged versions of the microporous metal–organic framework (MOF) known as MnMnBTT (BTT = 1,3,5-benzenetristetrazolate). By exploiting the dispersive differences between Mn, Fe, Cu, and Zn, the extent and location of cation exchange were determined from single crystal X-ray diffraction data sets collected near the K edges of Mn2+ and of the substituting metal, and at a wavelength remote from either edge as a reference. Comparing the anomalous dispersion between these measurements indicated that the extent of Mn2+ replacement depends on the identity of the substituting metal. We contrasted two unique methods to analyze this data with a conventional approach and evaluated their limitations with emphasis on the general application of this method to other heterometallic MOFs, where site-specific metal identification is fundamental to tuning catalytic and physical properties.