Crystal structure of orthorhombic ferrous nitroprusside: Fe[Fe(CN)₅NO].2H₂O

Abstract

Ferrous nitroprusside can be obtained in three structural modifications: two different unstable phases, monoclinic trihydrate and cubic pentahydrate, and the stable one, an orthorhombic dihydrate. This contribution reports the crystal structure of the last one. Cell parameters are: a = 13.9734 ͑2͒, b = 7.4274 ͑1͒, and c = 10.4697 ͑1͒ Å; with four formula units per cell ͑Z =4͒. The crystal structure was refined from the corresponding XRD powder pattern using the Rietveld method. Final agreement factors of the refinement process were R wp = 8.46, R p = 6.54, and S = 1.38. The crystal structure is formed by a tridimensional assembling of the ͓Fe͑CN͒ 5 NO͔ molecular block through iron atoms bounded at the N end of the CN ligands. The NO group remains unlinked at its O atom. The octahedral coordination of the assembling metal is completed with a coordinated water molecule which stabilizes a second water through a strong hydrogen bond interaction. The tridimensional structure appears as piled up rippled sheets leading to a system of interconnected small cavities which increase their available volume on the material dehydration. This complex loses its crystal water below 100°C and then remains stable up to above 160°C when the decomposition process begins with the loss of the NO ligand. © 2005 International Centre for Diffraction Data.

Crystal structures of cubic nitroprussides: M[Fe(CN)5NO]·xH2O(M=Fe, Co, Ni). Obtaining structural information from the background

“…The M(2+) octahedron is also axially distorted along the axial cyanide nitrogen, and more electronegative than the water molecule oxygen atom. Such geometry around the metal centers agrees well with previously reported nitroprusside structures (Mullica et al , 1989, 1990, 1991a, b, 1992, 1993; Benavante et al , 1997; Gómez et al , 2001, 2004; Rodríguez-Hernández et al , 2005), as opposed to the starting model of cobalt nitroprusside (Mullica et al , 1991b). The calculated bond distances (Table III) are within the expected values for nitroprussides according to the crystal structures derived from single crystals for some noncubic analogues (Mullica et al , 1989, 1990, 1991a, 1992, 1993; Benavante et al , 1997).…”

“…This is evident comparing the cell volume per formula unit for iron(2+) nitroprusside in its two structures (orthorhombic and cubic). For the cubic phase the cell volume per formula unit is 369 Å 3 while for the more compact orthorhombic structure it is 272 Å 3 (Reguera et al , 1996; Rodríguez-Hernández et al , 2005). This also favors the observed cell contraction on the water removal.…”

“…These properties suggest the convenience of a proper description of their crystal structure. Fortunately it has been carried out for practically all the divalent transition metals (Mullica et al , 1989, 1990, 1991a, b, 1992, 1993; Benavante et al , 1997; Gómez et al , 2001, 2004; Reguera et al , 1996; Rodríguez-Hernández et al , 2005), except for the cubic phases of Fe(2+) and Ni(2+). For Co(2+) the reported structure (Mullica et al , 1991b) must be reconsidered.…”