The interplay of hydrogen bonds in the solid state structure of NH-pyrazoles bearing cyano and amino substituents

► The annular tautomerism of two 4-cyano-3(5)-aminopyrazoles has been studied. ► The 3-amino-tautomer found to be more favorable form for the free molecules. ► The 3-amino-tautomer is the sole form in the solid state by X-ray.