Quantum-chemical calculation methods have been used to examine an influence of
tautomeric equilibrium [Azo
Hydrazo] on a structure of 1:2 chromium metal
complex dyes called
Gryfalan Navy Blue RL (CI 15 707, Acid Blue 193) and
Gryfalan
Black RL (Acid Black 194). Chromatographic analysis indicates that synthesis yields
a mixture of several dyes with different shades. Studies conducted to date have suggested
that such dye complexes can constitute Drew-Pfitzner or Pfeiffer-Schetty
structural isomers [1]. It is a know fact, that o-hydroxy-azo dyes exist in equilibrium
of tautomeric azo and hydrazone forms. We decided to examine, whether color
properties of examined metal-complex dyes can be influenced also by an azo-hydrazone
equilibrium and what kind of influence on it has sulphonic groups present
in molecules. Calculation and optimization of the geometrical structure were performed
using the AM1 methods for monoazoo-hydroxy-azo dyesand ZINDO/1 for
1:2 chromium metal complex dyes. It was stated that monoazo dyes can create complexes
in both forms: azo and hydrazone, because energy differences between each
form of the metal complex dye are so small, that the monoazo dye can, in practice,
create complexes in both the azo and the hydrazone form, with energy differences
not exceeding about 4 - 11 kcal/mol. It is calculated that spatial structure changes
with an angle of about 90° between two molecules of the dye, and angles of 10° - 20°
between the naphthalene moieties. Similar electron density on the hydroxyl and ketone
groups suggests that the mixture contains a dominant share of the azo form.
The presence of an ionised sulphonic group was also found to affect on the tautomer
equilibrium.