| Summary: | Crystallizing the cobalt(II) salt of the azo dye Orange G from water was found to give the solvent-separated ion-pair species hexaaquacobalt(II) 7-oxo-8-(2-phenylhydrazin-1-ylidene)-7,8-dihydronaphthalene-1,3-disulfonate tetrahydrate, [Co(H2O)6](C16H10N2O7S2)·4H2O. The asymmetric unit of the cobalt(II) salt contains three independent octahedral [Co(OH2)6]2+ cations, three azo anions, all with similar configurations, and 12 uncoordinated water molecules. The structure is closely related to that of one of the known magnesium analogues. Both structures have Z′ = 3, feature nearly planar azo anions [maximum displacement of azo-N atoms from the plane of the phenyl ring = 0.058 (7) Å] in their hydrazone tautomeric form, form layer structures with hydrophilic and hydrophobic layers alternating along the b-axis direction, and are stabilized by an extensive network of hydrogen bonds..
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