In Search of the True Structure of the Sodium Chromium Alum II: Crystal Growth and Structure of the Double Salt NaCr(SO_4)_2(H_2O)_6?(CH_3OH)_(0.6(2))? (H_2O)_(1.5(5))

摘要

Attempts to crystallize the sodium chromium alum, NaCr(SO_4)_2(H_2O)_(12), from water/methanol solutions at temperatures around 281 K yielded crystals of the title compound instead. Their monoclinic structure can be described as a centered rectangular array of linear {_∞~1}[Na(SO_4)_2]~(3-) rods aligned parallel to [001] with vicinal rods held together by columns of isolated [Cr(H_2O)_6]~(3+) complexes. The structure forms channels parallel to [001] which are occupied by methanol and water molecules with atomic site occupancy factors of 1/5 and less. Various attempts to crystallize the compound or the sodium chromium alum from purely aqueous solutions remained unsuccessful.