Isostructural behaviour in ammonium and potassium salt forms of sulfonated azo dyes

Alan R. Kennedy, Jennifer B. A. Kirkhouse, Karen M. McCarney, Olivier Puissegur

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The structures of five ammonium salt forms of monosulfonated azo dyes, derivatives of 4-(2-phenyldiazen-1-yl)benzenesulfonate, with the general formula [NH 4][O 3S(C 6H 4)NN(C 6H 3)RR 0]·XH 2O [R = OH, NH 2 or N(C 2H 4OH) 2; R 0 = H or OH] are presented. All form simple layered structures with alternating hydrophobic (organic) and hydrophilic (cation, solvent and polar groups) layers. To assess for isostructural behaviour of the ammonium cation with M + ions, the packing of these structures is compared with literature examples. To aid this comparison, the corresponding structures of four potassium salt forms of the monosulfonated azo dyes are also presented herein. Of the five ammonium salts it is found that three have isostructural equivalents. In two cases this equivalent is a potassium salt form and in one case it is a rubidium salt form. The isostructurality of ion packing and of unit-cell symmetry and dimensions tolerates cases where the ammonium ions form somewhat different interaction types with coformer species than do the potassium or rubidium ions. No sodium salt forms are found to be isostructural with any ammonium equivalent. However, similarities in the anion packing within a single hydrophobic layer are found for a group that consists of the ammonium and rubidium salt forms of one azo anion species and the sodium and silver salt forms of a different azo species.

Original languageEnglish
Pages (from-to)66-79
Number of pages14
JournalActa Crystallographica Section C: Structural Chemistry
Issue numberPt. 3
Early online date15 Feb 2024
Publication statusPublished - 1 Mar 2024


  • single-crystal X-ray diffraction
  • dye
  • salt selection
  • sulfonated azo
  • alkali metal
  • crystal structure
  • isostructural


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