Four crystal-structures derived from a yellow pyrazolyl azo pigment

The title compound is a pyrazolyl azo pigment which has good light- and heat-stability, but is rather poor in solvent fastness. X-ray structure analysis has been carried out in order to improve its solvent fastness from the structural point of view. Unexpectedly, two kinds of five-coordinate bisazo Na-complexes (Na-containing B-PAT: space group: P-1) as well as one Na-free monoazo compound (M-PAT: space group: C2/c) were isolated as single crystals. NaNO2 used for the preparation of diazo components is found to be responsible for the Na-complex formation, and the Na atom bridges two monoazo moieties in a cis fashion. On the other hand, elimination of the Na atom by hydrochloric acid yields a Na-free bisazo compound of the trans form (Na-free B-PAT: space group: P-1). Na-free B-PAT is characterized by good solvent fastness in addition to the light- and heat-stability of the original title compound.