To study the electrolyte ion adsorption in Ni3(HITP)2 using NMR techniques, powdered MOF samples were combined with different loading volumes of 1 M tetraethylammonium tetrafluoroborate in deuterated acetonitrile (1 M NEt4BF4/d3ACN) electrolyte, and F NMR spectra were recorded to investigate the BF4 -anion environments. (Figure ). Each 19 F NMR spectrum revealed two resonances, indicative of two major BF4 -anion environments in the system, which can be initially assigned to 'in-pore' and 'ex-pore' environments (SI Figure ). The peak at approx. -145.5 ppm is assigned to in-pore anions as it is shifted by a greater extent away from the neat electrolyte due to MOF-anion interactions, while the peak at approx. -148.5 ppm is much closer to the neat electrolyte's chemical shift and is assigned to ex-pore BF4 -species. The in-pore peak is additionally identified by more intense magic-angle spinning (MAS) sidebands, which from fitting various spectra of various samples with a chemical shift anisotropy (CSA) model (SI Table ) consistently indicated a greater anisotropy experienced in this confined electrolyte environment compared to the more mobile ex-pore electrolyte despite variation in the absolute CSA value between samples.