Diselenium pentoxide

Diselenium pentoxide can be prepared by thermal decomposition of selenium trioxide at about 450 K, Reaction (V.3). It is a white, hygroscopic solid that starts to decompose slowly above 455 K according to  

The compound melts at (497 1) K under violent disintegration, [62JER/MEN], [72SID/KON]. The crystal structure of 86205 was determined by Zak [80ZAK]. The structure is composed of alternating SeO and Se02 units joined by O bridges into infinite chains, [-Se (0)-0-Se (02)-0-] . 

Jerschkewitz and Menning [62JER/1VIEN] measured the enthalpy of dissolution of Se205(cr) in water to a coneentration of 0.018 M to be - (114.2 0.4) kJ-mol . This datum has been combined with the enthalpies of dissolution to the same concentration of Se02(cr), (5.06 0.24) kJ-mol , found in [61SEL/PAK] and of SeO ,(er), 

Changes in A //° ((V.7)) between 293 and 298 K have been neglected and a correction, calculated to be (0.60 0.20) kJ-mol, for different degrees of protolysis has been applied. 

The selected enthalpies of formation of Se02(cr) and Se03(cr), and A,//° (V.7) give the selected value  

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Diselenium pentoxide can also be formed as a product in the reaction of selenium dioxide difluoride with Se02. Measurements of molten Se20s suggest that [SeO]+ and [Se04] ions are present. The stmcture of crystalline Sc205 is that of a linear polymer with alternating Se and Se atoms (12), which has been confirmed by means of Raman spectroscopy. 

ZAK] Zak, Z., Crystal structure of diselenium pentoxide Sc205, Z. 

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