Zur Polymorphie des Ba(BrO3)2 und Sr(IO3)2, Kristallstruktur, röntgenographische, schwingungsspektroskopische und thermoanalytische Untersuchungen / Polymorphism of Ba(BrO3)2 and Sr(IO3)2 — Crystal Structure, X-Ray, IR, Raman, and Thermoanalytical Data

The polymorphic behaviour of Ba(BrO3)2 and Sr(IO3)2 is studied by means of differential thermal analyses and high-temperature X-ray and Raman spectroscopic measurements. On dehydration of the respective monohydrates [Ba(ClO3)2 · H2O type] at low temperatures in a vacuum Ba(BrO3)2 I and α-Sr(IO3)2 (both α-Ba(IO3)2 type, space group C2/c, Z = 4) are formed. On heating these polymorphs above 145 and 240 °C, respectively, phase transitions to Ba(BrO3)2 II [Sr(ClO3)2 type] and the hitherto unknown γ-Sr(IO3)2 occur. On further heating Ba(BrO3)2 II decomposes [partly via the high-temperature polymorph Ba(BrO3)2 III] to BaBr2 and O2, γ-Sr(IO3)2 via the probably only stable polymorph β-Sr(IO3)2 to iodine and strontium paraperiodate. The IR and Raman spectra of Ba(BrO3)2 I and III, α-, β- and γ-Sr(IO3)2, and α-Ba(IO3)2 are given. The crystal structure of Ba(BrO3)2 I has been determined by single crystal X-ray diffraction. The final R value for 1586 reflections with I ≥ 2σI is 0.064. The crystal structures of the a-Ba(IO3)2 type anhydrous halates are very similar to those of the Ba(ClO3)2 · H2O type halate monohydrates.