PREFERENTIAL UPTAKE OF AMMONIUM-IONS BY ZINC FERROCYANIDE

The concentration of ammonia from dilute aqueous solution could have f acilitated many prebiotic reactions. This may be especially true if th is concentration involves incorporation into an organized medium. We h ave shown that (unlike iron(III) ferrocyanide) zinc ferrocyanide, Zn-2 Fe(CN)(6) . xH(2)O, preferentially takes up ammonium ions from 0.01 M NH4Cl to give the known material Zn-3(NH4)(2)[Fe(CN)(6)](2) . xH(2)O, even in the presence of 0.01M KCl. KCl alone gave Zn3K2[Fe(CN)(6)](2) . xH(2)O. Products were characterized by elemental (CHN) analysis and powder X-ray diffraction (XRD). We attribute the remarkable specifici ty for the ammonium ion to the open framework of the product, which of fers enough space for hydrogen-bonded ammonium ions, and infer that ot her inorganic materials with internal spaces rich in water may show a similar preference.