Method of synthesis of unsolvated mixed cation borohydrides

A method of synthesis of unsolvated mixed cation borohydrides having a general formula MxM′y(BH4)2, where M and M′ stand for metal cations, x, y and z are stoichiometric coefficients, characterized in that the precursors having a general formula M[An]u and [Cat]vM′(BH4)w are used for the synthesis, where [An] stands for a weakly coordinating anion;

• [Cat] stands for weakly coordinating cation;
• u, v and w are the stoichiometric coefficients;
• and the synthesis is carried out under an inert to the reagents atmosphere according to the general reaction equation:
• xM[Ah]u+y[Cat]vM′(BH4)w→MxM′y(BH4)z+xu[Cat][An]
• where z=yw, xu=yv;
• MxM′y(BH4)z is the product of the reaction;
• [Cat][An] is the by-product of the reaction which can be separated from the product using a properly selected solvent or a mixture of solvents, which neither dissolves, nor solvates the product MxM′y(BH4)z, while completely dissolves the by-product [Cat][An].