In-situ X-ray powder diffraction studies of hydrothermal and thermal decomposition reactions of basic bismuth(III) nitrates in the temperature range 20-650 °C

The syntheses of basic bismuth(III) nitrates under hydrothermal conditions and their dry decomposition to (alpha) -Bi2O3 in solid-state reactions was investigated by in-situ synchrotron X-ray radiation powder diffraction. Three basic bismuth(III) nitrates with known structures are: [Bi6O4(OH)4](NO3)6·4H2O, C, [Bi6O4(OH)4](NO3)6·H2O, D, and [Bi6O5(OH)3](NO3)5·3H2O, A. They contain the complex ions [Bi6O4(OH)4]6+ and{[Bi6O5(OH)3]5+}2, respectively. A fourth basic bismuth(III) nitrate, X, apparently has the composition [Bi6O4.5(OH)3.5](NO3)5.5·H2O according to chemical analysis. The transformation of C via D to X, or of C directly to X was established in the in-situ hydrothermal synthesis. Similarities in the decomposition paths of C, D and X in the solid-state in-situ investigations support the above composition indicated for X. The compound A has a decomposition path different from those of C, D and X. This is consistent with the complex ion {[Bi6O5(OH)3]5+}2 in A, being different from the complex ion [Bi6O4(OH)4]6+ in the other two basic bismuth(III) nitrates. All four compounds have (alpha)-Bi2O3 as the final decomposition product.