Solvent induced temperature dependencies of NMR parameters of hydrogen bonded anionic clusters

The solvent induced temperature dependence of NMR parameters (proton and fluorine chemical shifts, the two-bond scalar spin coupling constant across the hydrogen bridge, (2h)J(FF)) for dihydrogen trifluoride anion, (FH)(2)F-, in a polar aprotic solvent, CDF3/CDF2Cl, is reported and discussed. The results are interpreted in terms of a simple electrostatic model, accounting a decrease of electrostatic repulsion of two negatively charged fluorine atoms on placing into a dielectric medium. The conclusion is drawn that polar medium causes some contraction of hydrogen bonds in ionic clusters combined with a decrease of hydrogen bond asymmetry. (C) 2003 Elsevier B.V. All rights reserved.