Synthesis and crystal structure characterization of Na[Fe₄S₃(NO)₇]·5H₂O

The crystal structure of a sodium iron-sulfur nitrosyl cluster salt, namely, catena-poly[[[diaquasodium(I)]-di-μ-aqua-[diaquasodium(I)]-di-μ-aqua] bis{heptanitrosyltri-μ₃-sulfido-tetrairon(3 Fe-Fe)] dihydrate], {[Na₂(H₂O)₈][Fe₄S₃(NO)₇]₂·2H₂O}_n, was determined by single-crystal X-ray diffraction. The crystal belongs to the orthorhombic system, space group Pna2₁. The structure retains the typical [Fe₄S₃(NO)₇]^- incomplete cubane-type core skeleton and its geometric configuration is similar to those of reported alkali metal Roussin's black salts, such as the caesium salt. Owing to the strong hydration effect of Na⁺, one-dimensional polymeric hydrated sodium chains extending along the a axis and a supramolecular network are formed via coordination and O-H...O hydrogen bonds with the water molecules. The crystal packing is primarily driven by this hydrogen-bonded network, accompanied by localized positional disorder of the lattice water molecules and a 60° rotational disorder of the anions around a pseudo-threefold axis. By introducing an inversion twin model and applying appropriate geometric and displacement parameter restraints, these crystallographic disorders were properly handled during the refinement.