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Tautomerism, crystal structure, and copper( II ) complexation of isomeric pyridonylazo dyes derived from 2‐ and 4‐aminobenzoic acids
Author(s) -
Wang YueHua,
Qian HuiFen,
Feng YaNan,
Huang Wei
Publication year - 2016
Publication title -
coloration technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.297
H-Index - 49
eISSN - 1478-4408
pISSN - 1472-3581
DOI - 10.1111/cote.12235
Subject(s) - chemistry , tautomer , hydrazone , pyridine , diazo , thermogravimetric analysis , copper , aminobenzoic acid , thermal stability , ligand (biochemistry) , crystallography , photochemistry , medicinal chemistry , inorganic chemistry , organic chemistry , biochemistry , receptor
A pair of isomeric aromatic heterocyclic dyes, bearing the same N ‐methyl pyridine‐2,6‐dione coupling component but a different 2‐ or 4‐aminobenzoic acid diazo component, were characterised structurally and spectroscopically. X‐ray single‐crystal diffraction analyses revealed that they both adopt the same hydrazone‐tautomeric form and planar molecular conformation between the pyridine and phenyl rings. Furthermore, azo–hydrazone transformation was achieved for the 2‐aminobenzoic‐acid‐based dye after Cu( II ) ion complexation, as verified by the formation of a neutral Cu( II ) dye–metal complex. The coordination geometry of the central Cu( II ) ion exhibits a slightly distorted pyramid with a τ value of 0.028, where the ligand loses a proton during complexation and serves as the tridentate coordination mode. In addition, thermogravimetric analysis and corresponding differential thermal analysis for the isomeric pair showed that they both have excellent thermal stability, and 4‐aminobenzoic‐acid‐based dye has a higher decomposition temperature (319 °C) than the 2‐aminobenzoic‐acid‐based dye (312 °C). To the best of our knowledge, this is the first structural study on aromatic heterocyclic dyes having aminobenzoic acid and pyridine‐2,6‐dione components at the same time.