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

Abstract

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.

New Supramolecular Hypoxia-Sensitive Complexes Based on Azo-Thiacalixarene

“…However, the preferred interaction of macrocycle L with Rh6G cannot be explained only from the standpoint of electrostatic interactions. Taking into account the great difference in the logP values of Rh6G and Rh123 (6.5 and 1.5), as well as the difference in logD values (2.1. and 0.5., respectively [ 37 ], it can be assumed that the comparatively high hydrophobicity of Rh6G favors the interactions with the hydrophobic basket of calixarene. The association constants ( K ass ) of azo-thiacalixarene L and rhodamine dyes were determined by fitting the data of the fluorescence titration ( Table 1 ).…”

Azocalix[4]arene-Rhodamine Supramolecular Hypoxia-Sensitive Systems: A Search for the Best Calixarene Hosts and Rhodamine Guests

“…Thus, the preferred interaction of macrocycles 1 , 2 and 4 with Rh6G cannot be explained only from the standpoint of electrostatic interactions. Taking into account the great difference in the logP values of Rh6G and Rh123 (6.5 and 1.5), as well as the difference in logD values (2.1 and 0.5, respectively) [ 30 ], it can be assumed that the comparatively high hydrophobicity of Rh6G favors the interactions with the hydrophobic basket of calixarene.…”

Novel Monosulfonated Azo Dyes: Design, Synthesis, and Application as Disperse Dyes on Polyester Fabrics

“…1−8 Certain compounds contain sulfonated moieties that deserve particular attention because they can be used as disperse dyes and for their wide range of biological and analytical applications. 9 Extraordinary studies have been conducted on salt forms of monosulfonated azo dyes 10,11 and disulfonated azo dyes. 12 Due to their various elegant characteristics, e.g., color, light fastness, solubility, etc., many sulfonated azo dyes are on the market (Figure 1).…”

“…Extraordinary studies have been conducted on salt forms of monosulfonated azo dyes , and disulfonated azo dyes . Due to their various elegant characteristics, e.g.…”