Biologically active complex

A process for preparing an aqueous solution comprising at least one species selected from the group consisting of a 1:1 molar complex of TeO2 with a moiety of formula (A) and ammonium salts thereof:

• HO—X—OH (A)
• where X is an optionally substituted divalent saturated hydrocarbon group containing 2-8 carbon atoms in the chain connecting the two OH groups the process comprising:
• (i) a reactant selected from:
• a telluric(IV) halide having the formula X(—O—)2Te(hal)2,
• a telluric(IV) bis-ester having the formula X(—O—)2Te(—O—)2X1, and
• an ammonium salt having the formula (NH4)+[X(—O—)2Te(hal)3]−,
• where X and X1 are each independently selected optionally substituted divalent saturated hydrocarbon groups containing 2-8 carbon atoms in the chain, and hal is a halogen atom,
• is subjected to hydrolysis in an aqueous medium;
• or
• (ii) said aqueous solution obtained in (i) is mixed with an ammonium salt of a salt-forming acid in an aqueous medium, in order to convert the solution of complex, with the proviso that the complex is not in an ammonium salt form, to the ammonium salt form.