Region-Resolved Diffraction for Decoding Crystal Heterogeneity via Multi-Energy Metal Discrimination

Multivariate metal–organic frameworks (MTV‑MOFs) with controlled metal sequencing offer a versatile platform for tuning catalysis, sorption, and optical properties, but their performance is governed by the real spatial distribution of metals within individual crystals rather than by bulk compositions. Building on the sequencing strategies demonstrated in “Sequencing of metals in multivariate metal-organic frameworks” (Science, 2020, 367, 1473–1476, DOI: 10.1126/science.aaz4304), this project targets a direct crystallographic visualization of metal composition profiles along the growth direction (“height”) of single MOF crystals. Conventional powder and single‑crystal diffraction, as well as bulk spectroscopies, average over entire crystals and cannot resolve micro‑heterogeneities, interfaces between growth stages, or local deviations from ideal metal sequences.

We propose to exploit an MX microfocus beamline with a tunable, highly focused X‑ray beam to perform position‑resolved anomalous diffraction on mixed‑metal MOF crystals. By rastering a micrometer‑sized beam along the long axis of individual crystals and collecting datasets at carefully chosen energies around the absorption edges of the constituent metals, we will refine site occupancies as a function of position and obtain quantitative metal composition profiles. These measurements will be correlated with unit‑cell parameters and diffuse scattering signatures to connect local composition with structural disorder or strain.

The specific aims are: (i) to establish robust experimental and data‑analysis protocols for spatially resolved anomalous diffraction on beam‑sensitive MOFs; (ii) to quantify how closely experimental metal profiles follow the targeted sequences under different synthesis and post‑synthetic exchange conditions; and (iii) to use these insights to refine mechanistic models of MOF crystal growth and sequence encoding. The project will deliver a general methodology for probing micro‑scale compositional heterogeneity in porous crystals and demonstrate a powerful new application domain for MX microfocus beamlines.