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

The hitherto unknown tetrabromozincates Li2ZnBr4 and Na2ZnBr4 have been prepared. Quaternary halides Li2Zn(Cl, Br)4 and Li2Zn(Br, I)4 have been not obtained due to decomposition to mixtures of LiCl and ZnBr2, and 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 spectroscopy) are presented and discussed. Contrary to Li2ZnCl4, Li2ZnBr4 and Na2ZnBr4 do not undergo any phase transition between 20-degrees-C and their melting points.