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Article

Monosulfonated Azo Dyes: A Crystallographic Study of the Molecular Structures of the Free Acid, Anionic and Dianionic Forms

1
Department of Pure & Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, UK
2
Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA
3
Department of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Manchester M13 9PL, UK
*
Author to whom correspondence should be addressed.
Crystals 2020, 10(8), 662; https://doi.org/10.3390/cryst10080662
Received: 20 June 2020 / Revised: 13 July 2020 / Accepted: 16 July 2020 / Published: 1 August 2020
(This article belongs to the Special Issue Structure and Properties of Organic Dyes in Solid State)
Crystallographic studies of monosulfonated azo dyes have concentrated on the salt forms that contain the azo anion. Here we present a study that compares the structures of these anions with protonated free acid forms and with doubly deprotonated dianion forms. To this end, the new single crystal diffraction structures of 13 systematically related free acid forms of monosulfonated azo dyes are presented, together with three new structures of doubly deprotonated forms and two new structures of Na salt forms of azo anions. No structures of dideprotonated monosulfonated azo dyes have previously been reported and this paper also reports the first crystal structure of an azo dye with a hydronium cation. The geometries of the free acid, anion and dianion forms are compared to literature equivalents. It is shown that protonation of the azo bond gives predictable bond lengthening and shortening, which is of a greater magnitude than similar effects caused by azo-hydrazone tautomerisation, or the smaller again effects caused by the resonance electron donation from O or N based substituents. The dianion containing structures have twisted dianion geometries that can be understood based on the resonance effects of the phenoxide groups and upon the needs to bond to a relatively high number of metal cations. View Full-Text
Keywords: dyes; sulfonate; free acid; salt forms; hydronium; coordination polymer; crystalline polymorphism; crystallography dyes; sulfonate; free acid; salt forms; hydronium; coordination polymer; crystalline polymorphism; crystallography
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MDPI and ACS Style

Kennedy, A.R.; Conway, L.K.; Kirkhouse, J.B.A.; McCarney, K.M.; Puissegur, O.; Staunton, E.; Teat, S.J.; Warren, J.E. Monosulfonated Azo Dyes: A Crystallographic Study of the Molecular Structures of the Free Acid, Anionic and Dianionic Forms. Crystals 2020, 10, 662. https://doi.org/10.3390/cryst10080662

AMA Style

Kennedy AR, Conway LK, Kirkhouse JBA, McCarney KM, Puissegur O, Staunton E, Teat SJ, Warren JE. Monosulfonated Azo Dyes: A Crystallographic Study of the Molecular Structures of the Free Acid, Anionic and Dianionic Forms. Crystals. 2020; 10(8):662. https://doi.org/10.3390/cryst10080662

Chicago/Turabian Style

Kennedy, Alan R.; Conway, Linda K.; Kirkhouse, Jennifer B.A.; McCarney, Karen M.; Puissegur, Olivier; Staunton, Edward; Teat, Simon J.; Warren, John E. 2020. "Monosulfonated Azo Dyes: A Crystallographic Study of the Molecular Structures of the Free Acid, Anionic and Dianionic Forms" Crystals 10, no. 8: 662. https://doi.org/10.3390/cryst10080662

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