Changes in the 13C NMR spectra of tetra-n-butylammonium chloride by clathrate hydration.

• The guest-host interaction of the semi-clathrate hydrate was studied by 13C NMR. • The interaction and guest mobility in the range of 230–264 K were revealed. • The number of 13C NMR signals was different depending on the carbon position. • The cation's local structure was drastically changed with decreasing temperature. We report changes in the 13C NMR spectra of tetra- n -butylammonium (TBA) cations by clathrate hydration of TBA chloride (TBAC), which is a quaternary ammonium salt known to form a semi-clathrate hydrate expected as gas capture or cold storage materials. Clathrate hydration decreased the number of 13C NMR signals of the four carbons in comparison to the corresponding carbon signals in the solid phase at same temperatures. This is caused by the overall broadening of the signals due to incorporation of TBA cations into the hydrate framework, suggesting that the guest mobility is restricted by clathrate hydration. Furthermore, a comparison of the 13C NMR spectra between the TBAC hydrate and solid-state TBAC in the temperature range of 230–264 K suggested that having the rigid hydrate framework tended to restrict the guest mobility and changes in the local interaction of guest TBA cations with the hydrate framework with decreasing temperature. [ABSTRACT FROM AUTHOR]