Applications brief: Assessing Chemical Heterogeneity at the Nanoscale in Mixed-Ligand Metal-Organic Frameworks with the PTIR Technique

Key points


  • AFM-IR identifies complex Metal Organic Framework (MixMOF) micro-crystals at the nanoscale. Individual MixMOF micro-crystals are examined for the first time
  • Engineering anisotropic domains in MOF crystals with sub-micron linker concentration gradients
  • Heterogeneous and homogenous imaging of single crystallite domains
  • Potential to engineer more efficient catalysts and sensors

Key words

AFM-IR | Metal-Organic Framework | MixMOF | Infrared Spectroscopy | Nanoscale Chemical Imaging

Authors

Aaron M. Katzenmeyer, Jerome Canivet, Glenn Holland, David Farrusseng, and Andrea Centrone

Abstract

Recently, the use of mixtures of organic building block linkers gave chemists an additional degree of freedom for engineering Metal Organic Framework (MOF) properties; but the chemical complexity of such MixMOF structures is poorly characterized by conventional techniques, hindering verification of rational design.

In this Communication the Photo Thermal Induced Resonance technique is applied to individual MixMOF micro-crystals to elucidate chemical composition with nanoscale resolution. Results show that MixMOFs isoreticular to In-MIL-68, obtained either directly from solution or by post-synthetic linker exchange, are homogeneous down to ≈ 100 nm.

Additionally, we report a novel in situ process that enables engineering of anisotropic domains in MOF crystals with sub-micron linker concentration gradients.

AFM-IR spectra of a monoligand MOF sample provides information on ligand homogeneity and determining whether the ligands are part of the framework. Further analysis allows monitoring growth of crystals in the MOF, performing compositional analysis on the crystals, and investigating where the ligand exchange takes place.
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