New aspects on the hydrogen bond donor (HBD) strength of 1-butyl-3-methylimidazolium room temperature ionic liquids

Improved hydrogen bond donor (HBD) strength parameters of 1-butyl-3-methylimidazolium room temperature ionic liquids (RTILs), acceptor number (AN) of Gutmann and α of Kamlet–Taft, have been determined using [Fe(phen)2(CN)2]ClO4 as an original solvatochromic probe. Each of the parameters shows an excellent correlation with the independently determined HBA strength β (Kamlet–Taft) of the anion which demonstrates that empirical polarity parameters of RTILs can be utilized independently of each other.