There is provided a process for preparing compounds of formula M.sup.3M.sup.1A.sub.2. The process comprises reacting a compound of formula M.sup.2M.sup.1A.sub.2 with a compound of formula M.sup.3X.sup.2, in the presence of at least one coordinating solvent. M.sup.1 can be chosen from B.sup.3+, Al.sup.3+, Ga.sup.3+, In.sup.3+, Tl.sup.3+, Fe.sup.3+, and Au.sup.3+; M.sup.2 can be chosen from Li.sup.+, Na.sup.+, K.sup.+, Cs.sup.+, (T.sup.1).sub.3Si--, and N(T.sup.2).sub.4.sup.+; M.sup.3 can be chosen from Cu.sup.+, Ag.sup.+, Li.sup.+, Na.sup.+, K.sup.+, Cs.sup.+, Rb.sup.+, Fr.sup.+, Au.sup.+, and Hg.sup.+; A can be chosen from S and Se; and X.sup.2 can be chosen from Cl.sup.-, Br.sup.-, I.sup.-, F.sup.-, CH.sub.3COO.sup.-, NO.sub.3.sup.-, and CN.sup.-. Such compounds can be used for various purposes in the field of electrochemistry.