Synthesis and crystal structures of three Schiff bases derived from 3-formyl-acetyl-acetone and o -, m - and p -amino-benzoic acid.

Treatment of 3-formyl-acetyl-acetone with the isomeric o -, m - and p -amino-benzoic acids led to the formation of the corresponding Schiff bases, namely, 3-[(2-carb-oxy-phenyl-amino)-methyl-idene]pentane-2,4-dione, 1 , 3-[(3-carb-oxy-phenyl-amino)-methyl-idene]pentane-2,4-dione, 2 , and 3-[(4-carb-oxy-phenyl-amino)-methyl-idene]pentane-2,4-dione, 3 , all C 13 H 13 NO 4 , that contain a planar amino-methyl-ene-pentane-2,4-dione core with a strong intra-molecular N-H⋯O hydrogen bridge. The carb-oxy-phenyl groups attached to the nitro-gen atom are almost coplanar to the central mol-ecular fragment. Depending on the position of the carboxyl unit, different supra-molecular structures with hydrogen-bonding networks are formed in the three title structures.