Phenyl-ring rotational disorder in the two-dimensional hydrogen-bonded structure of the 1:1 proton-transfer salt of the diazo-dye precursor 4-(phenyl-diazenyl)aniline (aniline yellow) with l-tartaric acid

Graham Smith, Urs D. Wermuth, David J. Young

Research output: Contribution to journalArticle


In the structure of the 1:1 proton-transfer compound from the reaction of l-tartaric acid with the azo-dye precursor aniline yellow [4-(phenyl - diazenyl)aniline], namely 4-(phenyl-di-az-enyl)-anilinium (2R,3R)-3-carb-oxy-2, 3-dihy-droxy-propano-ate, C12H12N3 +·C4H5O6 -, the asymmetric unit contains two independent 4-(phenyl-diazenyl)-anilinium cations and two hydrogen l-tartrate anions. The structure is unusual in that all four phenyl rings of the two cations have identical rotational disorder with equal occupancy of the conformations. The two hydrogen l-tartrate anions form independent but similar chains through head-to-tail carboxyl-carboxyl-ate O - H⋯O hydrogen bonds [graph set C(7)], which are then extended into a two-dimensional hydrogen-bonded sheet structure through hy-droxy O - H⋯O hydrogen-bonded links. The anilinium groups of the 4-(phenyl-diazenyl)-anilinium cations are incorporated into the sheets and also provide inter-nal hydrogen-bonded extensions, while their aromatic tails are layered in the structure without significant association except for weak π-π inter-actions [minimum ring centroid separation = 3.844 (3) Å]. The hydrogen l-tartrate residues of both anions exhibit the common short intra-molecular hy-droxy-carboxylate O - H⋯O hydogen bonds. This work provides a solution to the unusual disorder problem inherent in the structure of this salt, as well as giving another example of the utility of the hydrogen tartrate anion in the generation of sheet substructures in mol-ecular assembly processes.

Original languageEnglish
Pages (from-to)o345-o348
Number of pages4
JournalActa Crystallographica Section C: Crystal Structure Communications
Issue numberPart 7
Publication statusPublished - 16 Jul 2010
Externally publishedYes


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