Adsorption of nitric oxide in metal-organic frameworks: Low temperature IR and EPR spectroscopic evaluation of the role of open metal sites

• NO adsorption in MOFs studied by DRIFTS and EPR spectroscopy at low temperatures.
• Coordination of NO to metal sites of the MOFs could be confirmed.
• A predictment of the strength of the adsorption could be derived.
• Ni-CPO-27 and Co-CPO-27 are promising materials for NO storage applications.

The metal-organic framework materials M-MIL-100 (M = Al, Fe) and M-CPO-27 (M = Co, Ni) have been studied with respect to the adsorption of nitric oxide employing low-temperature ESR and IR spectroscopy. Exposure of the previously desolvated Ni (II) and Co (II) sites in CPO-27 leads to the formation of metal nitrosyl complexes that are stable up to temperatures of 393 K. A weaker bond is formed between the iron metal centers in the Fe-MIL-100 type materials and the nitric oxide molecule. Using in-situ DRIFT and EPR spectroscopy at low temperatures, the formation of Co-, Ni- and Fe–NO adducts is evident from the respective spectra, while specifically strong interactions are absent in Al-MIL-100 and Al/Cr-Mil-53.

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