Poly[tris{μ(2)-4-[4-(di-methyl-amino)-phenyl-diazenyl]benzene-sulfonato}tri-dioxane-tri-sodium(I)]

The title compound, [Na(3)(C(14)H(14)N(3)O(3)S)(3)(C(4)H(8)O(2))(3)](n), is a polynuclear complex which includes, in the monomeric unit, three units of Na(I)-4'-dimethyl-amino-azobenzene-4-sulfonate [known as methyl orange (MO)] and three molecules of dioxane (C(4)H(8)O(2)). These constitute three kinds of Na(I) centres, two of which are seven-coordinate while the third is five-coordinate. One of the seven-coordinate centres is coordinated by six O atoms from the sulfonate groups of four different MOs and by one O atom from dioxane. The other is coordinated by seven O atoms from the sulfonate groups of five different MOs. The five-coordinate centre is coordinated by three O atoms from the sulfonate groups of three different MOs and two O atoms from two different dioxanes. In the crystal structure, a one-dimensional polymer chain is formed along the a axis and this ensures the thermal stability of the title compound. It is also to be noted that the N=N bond lengths of the three azo groups are appreciably different [1.259 (4), 1.196 (4), and 1.253 (4) Å].