Tetramethylfluoroformamidinium hexafluorophosphate164298-23-1100 % similar 1,3-Dimethyl-2-fluoroimidazolium hexafluorophosphate164298-27-556 % similar Tetramethylammonium hexafluorophosphate558-32-732 % similar Ammonium hexafluorophosphate16941-11-030 % similar