Bismuth perchlorate is an inorganic compound of bismuth and perchloric acid with the formula . It contains bismuth in the +3 oxidation state. Both anhydrous bismuth perchlorate and hydrated forms are known; the normal hydrated salt has been isolated as the pentahydrate, . Bismuth perchlorate undergoes extensive hydrolysis in aqueous solution, producing oxo- and hydroxo-bismuth species.
Preparation Bismuth perchlorate pentahydrate can be prepared by dissolving bismuth(III) oxide in concentrated perchloric acid. Crystallization from 70% perchloric acid gives the pentahydrate.
Anhydrous bismuth perchlorate has been prepared by reacting anhydrous bismuth(III) chloride with anhydrous perchloric acid at approximately 25 °C.
Direct reaction of metallic bismuth with concentrated perchloric acid is unsuitable as a preparative method because violent explosive reactions have been reported on heating.
Properties Hydrolysis and aqueous chemistry Bismuth perchlorate is readily hydrolyzed. One solid product of hydrolysis is bismuthyl perchlorate, , which can be obtained by hydrolysis of bismuth perchlorate in moderately concentrated perchloric acid.
The chemistry in solution is more complicated than this overall reaction suggests. Bismuth(III) undergoes hydrolysis even in strongly acidic aqueous media, forming polynuclear oxo-hydroxo species. In perchlorate solutions, the ion becomes significant as the acidity decreases; hydrolysis was detected even in solutions containing an excess strong-acid concentration of about 1 mol dm−3.
In sufficiently acidic aqueous perchlorate solution, the hydrated Bi3+ ion is approximately eight-coordinate. EXAFS and large-angle X-ray scattering measurements gave a mean Bi–O distance of 2.41(1) Å. Raman spectroscopy of acidified bismuth perchlorate solutions gives a polarized band near 393 cm−1, assigned to the symmetric Bi–O stretching vibration of the hydrated bismuth(III) ion.
Complex formation Addition of hydrochloric acid to bismuth perchlorate solutions causes the hydrated bismuth(III) ions to be replaced progressively by chloro complexes. Raman studies have identified species including , and at increasing chloride concentrations. In a bismuth perchlorate solution containing a large excess of hydrochloric acid, the 393 cm−1 Bi–O band disappears and a new polarized Raman band appears at 266.5 cm−1, consistent with formation of chlorobismuth complexes.
Bismuth perchlorate also forms well-defined solvates with oxygen-donor solvents. The crystalline dimethyl sulfoxide complex contains eight-coordinate bismuth in a distorted square-antiprismatic environment, with a mean Bi–O distance of about 2.43 Å. In the corresponding complex with N,N′-dimethylpropyleneurea, , bismuth is six-coordinate with an approximately octahedral arrangement and a mean Bi–O distance of 2.324(5) Å.
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