Squaraines: crystal structures and spectroscopic analysis of hydrated and anhydrous forms of squaric acid-isoniazid species.

The crystal structures, synthesis procedure, thermal behavior, and spectroscopic properties of a new squaraine SqINH·H2O and its anhydrous arrangement are described. This squaraine is obtained through an acid-base reaction using squaric acid (H2Sq) and isoniazid (INH) as precursors. Both squaraines crystallize in the monoclinic system, but in different space groups: the hydrated and anhydrous arrangement crystallizes in the P2₁ and P2₁/c space group, respectively.