We recorded the 2 H NMR spectra for a broad temperature range between 67 and 316 K. In Fig. we show the measured, the simulated and the deconvoluted Pake-like spectra at 113 K and 143 K for the PIL [TEA-d16][OMs] (see Scheme 1). The 2 H spectra are a superposition of three Pake-doublets with DQCCs for the methyl deuterons (QCD3= 52 kHz), the methylene deuterons (QCD2= 170 kHz) and the ND deuteron (QND= 147 kHz). The measured DQCC for C-D in the methylene group of about 170 kHz is typical for sp 3 hybridized deuterocarbons and obviously describes the static pattern well. Usually the nuclear contribution to the electric field gradient decreases in the series sp, sp 2 and sp 3 . However, the extremely small value for the methyl deuterons of about 52 kHz indicates significant motional narrowing which is expected from fast methyl group rotation still present at low temperatures. Thus this value is similar to that of the fast reorienting methyl group in toluene-d3 for temperatures below Tg, or n-dodecane-d3 below melting point. The temperature dependent DQCCs for all C-D fragments are given in the SI. Here we would like to focus on the DQCCs of the N-D deuteron in the PIL [TEA-d16][OMs] compared to those in PIL [TEA-d1][OMs], differing in isotopical labelling of the ethylene groups. The DQCC of the N-D deuterons is determined by the magnitude of the electric field gradient (efg) at the position of the nucleus. This efg originates mainly from the electrons of N-D group that participates in hydrogen bonding (N-D•••O). It has been shown for molecular liquids that the DQCC is a sensitive probe for hydrogen bonding. For water, DQCC values decrease from the gas phase (308 kHz) via the liquid phase (~254 kHz) down to the ice value (214 kHz) due to increasing HB strength in this order. The N-D DQCCs of both PILs are shown in Fig. as a function of temperature between 67 K and 313 K. We clearly observe that the electric field gradient tensor at the nuclei of the N-D deuterons changes. Qualitatively, the behaviour is similar for the ND fragment in both PILs, [TEA-d1][OMs] and [TEA-d16][OMs]. First, we observe the real DQCC Q0 of about 147 kHz at 67 K. Since its value remains unchanged for T < 103 K, we can conclude that it is the value not averaged by bond librations. Overall, the DQCC of [TEA-d16][OMs] is significantly smaller than those of [TEA-d1][OMs] (149 kHz at 143 K) and [TEA-d1][NTf2] (161 kHz at 143 K). The reason is Coulombenhanced hydrogen bonding of the [TEA] cation with the strongest interacting anion [OMs].