STRUCTURAL RELATIONSHIP OF POTASSIUM HEXAHYDROXOSCANDATE(III), K3[SC(OH)6] WITH THE ISOTYPIC HYDROXOMETALLATES RB3[SC(OH)6], K3[CR(OH)6], AND RB3[CR(OH)6]

Ternary hydroxides M3I[M(III)(OH)6] with M1 = K, Rb and M(III) = Sc, Cr were obtained in the same way as K3[Cr(OH)6] [1] from alkali metal amides and d-metal nitrates by a comproportionation reaction of amide and nitrate ions in supercritical ammonia to elementary nitrogen and hydroxide ions at 523 K and 3 less-than-or-equal-to p(NH3) less-than-or-equal-to 6 kbar within 1 to 3 months. Their structures were determined by single crystal x-ray methods inclusive the positions of the hydrogen atoms. The ratio of size of r(M(I))/r(M(III)) is related to the symmetry of these hydroxometallates. Structural relationships between K3[Sc(OH)6] and Rb3[Sc(OH)6], K3(Cr(OH)6], Rb3[Cr(OH)6] and K4[CdCl6] [4] are discussed.