The structure of two orthorhombic nitroprussides: Cd[Fe(CN)₅NO]·2H₂O and Zn[Fe(CN)₅NO]·2H₂O

When zinc and cadmium nitroprussides, obtained as powders or single-crystals samples, are aged in air they lose crystallization water and change their crystalline structure. In the stable form these two complexes are orthorhombic dihydrates with four molecules in the unit cell. In the aging process the crystals become brittle producing a polycrystalline material. The crystalline structure of these two complexes (orthorhombic dihydrates) was refined from their XRD powder patterns using the Rietveld method. As the starting model in the refining process the reported orthorhombic structure of copper nitroprusside (dihydrate) was used. The main changes in the dehydration process associated with the structural transformation take place in the coordination sphere of the outer cation (Cd or Zn).