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, CDF 3 /CDF 2 Cl, 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.