Synthesis and crystal structures of three Schiff bases derived from 3-formyl­acetyl­acetone and o-, m- and p-amino­benzoic acid

Treatment of 3-formyl­acetyl­acetone with the isomeric o-, m- and p-amino­benzoic acids led to the formation of the corresponding Schiff bases, namely, 3-[(2-carb­oxy­phenyl­amino)­methyl­idene]pentane-2,4-dione, 1, 3-[(3-carb­oxy­phenyl­amino)­methyl­idene]pentane-2,4-dione, 2, and 3-[(4-carb­oxy­phenyl­amino)­methyl­idene]pentane-2,4-dione, 3, all C(13)H(13)NO(4), that contain a planar amino-methyl­ene-pentane-2,4-dione core with a strong intra­molecular N—H⋯O hydrogen bridge. The carb­oxy­phenyl groups attached to the nitro­gen atom are almost coplanar to the central mol­ecular fragment. Depending on the position of the carboxyl unit, different supra­molecular structures with hydrogen-bonding networks are formed in the three title structures.