NEW HALOGENOZINCATES M2IZNX4 (M(I) = LI, NA, X = CL, BR) OF OLIVINE TYPE

The hitherto unknown tetrabromozincates Li2ZnBr4 and Na2ZnBr4 have bee n prepared. Quaternary halides Li2Zn(Cl, Br)4 and Li2Zn(Br, I)4 have b een not obtained due to decomposition to mixtures of LiCl and ZnBr2, a nd LiBr and ZnI2. The crystal structures of the olivine-type bromides and of the high-temperature polymorph of Li2ZnCl4 have been determined by neutron powder diffraction using the Rietveld method (space group Pnma, Z = 4, a = 1360.41(4), b = 788.47(2), c = 647.07(2) pm, R(I) = 9 .07% (Li2ZnBr4), a = 1446.32(5), b = 853.02(3), c = 676.61(2) pm, R(I) = 9.29% (Na2ZnBr4), a = 1277.60(3), b = 741.76(2), c = 611.10(1) pm, R(I) = 7.63% (Li2ZnCl4)). The Raman spectra as well as the results of thermal analyses (DSC) and conductivity measurements (impedance spectr oscopy) are presented and discussed. Contrary to Li2ZnCl4, Li2ZnBr4 an d Na2ZnBr4 do not undergo any phase transition between 20-degrees-C an d their melting points.