Crystal structure, infrared and Raman spectra and thermal analysis of strontium-tetrahydrogen-hexaoxoperiodate-trihydrate, Sr(H4IO6)2·3H2O

By crystallization from a strongly acidic aqueous solution strontium-tetrahydrogen-hexaoxoperiodate-trihydrate Sr(H 4 IO 6 ) 2 ·3H 2 O has been obtained. In the structure of this compound (S.G. P 1 ,Nr.2, Z =2, a =636.1(1) pm, b =993.9(2) pm, c =1044.5(2) pm, α =114.54(3)°, β =95.61(3)°, and γ =97.11(3)°) two crystallographically different H 4 IO 6 − anions are linked by two and three common oxygen atoms, respectively, to SrO 5 (H 2 O) 4 polyhedra which are of the form of monocapped distorted square antiprisms. The IR- and Raman-spectra of this compound are analyzed with respect to the internal vibrations of the periodate anion and the O–H vibrations of the hydrogen bonds. The dehydration and decomposition of the compound, studied by thermal analysis, high temperature Raman experiments and mass spectrometric analysis of the evolved gases, takes place via an unknown metaperiodate Sr(IO 4 ) 2 , results at 265 °C in the formation of Sr(IO 3 ) 2 in an exothermic reaction and finally Sr 5 (IO 6 ) 2 is formed in a disproportionation reaction.