The compound of claim 1 wherein A' is a compound corresponding to the empirical formula: (AlArf 3-w' Q1 w')w (AlArf 3-x' (OQ2)x')x (AlQ1 3-y' (OQ2)y')y [(--AlQ2 --O--)z' ]z, where;Arf is a fluorinated aromatic hydrocarbyl moiety of from 6 to 30 carbon atoms; Q1 is C1-20 alkyl; Q2 is C1-20 hydrocarbyl, optionally substituted with one or more groups which independently each occurrence are hydrocarby