Temperature-dependent 11B spin-lattice relaxation time for BF4 and CF3BF3 anions in room-temperature ionic liquids

Temperature‐dependent 11B T1 values were measured for the BF4 anion and BF3 in the CF3BF3 anion in room‐temperature ionic liquids (RTILs) composed of the cation N‐diethyl‐N‐methyl‐N‐(2‐methoxyethyl)ammonium (DEME). Including the lithium‐salt‐doped samples, two neat and two binary ionic liquids were studied. Arrhenius plots of the 11B T1 showed T1 minima for BF4 in the temperature range between 243 (or above freezing) and 373 K. Using the Bloembergen, Pound, and Purcell(BPP) equations for the 11B quadrupolar and 11B19F dipolar relaxation mechanisms, the correlation times for motions of BF4 were calculated. Since the internal rotation of BF3 is assumed in CF3BF3, T1 minimum was not observed. The effects of the addition of the lithium salt on the 11B correlation time and 11BT1 for the anions in the ILs are discussed. Copyright © 2010 John Wiley & Sons, Ltd. The temperature dependent correlation times of 11B were derived from the 11B T1 minimum of the Arrhenius plots for an anion BF4 in room‐temperature ionic liquids composed of a quaternary ammonium cation (DEME) and a lithium salt doped system.