Acetylenedicarboxylate and In Situ Generated Chlorofumarate-Based Hafnium(IV)–Metal–Organic Frameworks: Synthesis, Structure, and Sorption Properties

New acetylenedicarboxylate (ADC) and chlorofumarate (Fum-Cl) based hafnium-metal–organic frameworks have been synthesized by alternatively reacting acetylenedicarboxylic acid in DMF or water with appropriate hafnium salt, in the presence of acetic acid modulator. The two materials of respective ideal formulas [Hf6O4(OH)4(ADC)6] (Hf-HHU-1) and [Hf6O4(OH)4(Fum-Cl)6] (Hf-HHU-2) have been structurally characterized by powder X-ray diffraction to be UiO-66 isostructural, consisting of octahedral [Hf6O4(OH)4]12+ secondary building units each connected to other units by 12 ADC or Fum-Cl linkers into a microporous network with fcu topology. This structure was confirmed by Rietveld refinement. Hf-HHU-2 is formed by in situ hydrochlorination of acetylenedicarboxylic acid to chlorofumarate. Its presence has been determined by combined Raman spectroscopy, solid-state NMR, scanning electron microscopy, energy dispersive X-ray and X-ray photoelectron spectroscopies. Hf-HHU-1 and Hf-HHU-2 exhibit very high hydrophilicit...