The crystal structures of five N-(2,3-dihydroxybenzylidene)amine derivatives, C7H6NO2--R [R = phenyl (1), p-methylphenyl (2), o-chlorophenyl (3), isopropyl (4) and cyclopropyl (5)] are presented and discussed.

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In the title compound, C16H9ClO4, the dihedral angle between the coumarin ring system [maximum deviation = 0.023 (1) Å] and the benzene ring is 73.95 (8)°.

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In the title compound, C 16 H 10 O 4 , the dihedral angle between the coumarin ring system (r.m.s. deviation = 0.015 Å ) and the benzoate group is 83.58 (9) , which compares to a value of 81.8 obtained from a DFT calculation at the B3LYP/6-311 G(d,p) level. In the crystal, C-OÁ Á Á and C-HÁ Á Á interactions and aromatic -[CgÁ Á ÁCg = 3.7214 (14) and 3.7059 (14) Å ] stacking generate a three-dimensional network. Structure descriptionCoumarin-based ion receptors, fluorescent probes, and biological stains have extensive applications in monitoring enzyme activity as well as accurate pharmacological and pharmacokinetic properties in living cells (Chen et al., 2013;Guha et al., 2012). As part of our ongoing studies in this area, we now present herein the synthesis and structure of the title compound (Fig. 1).As expected, the coumarin ring system is almost planar, the maximum deviation from the plane of 0.022 (2) Å is for atom C9. The torsion angles C10-C8-O4-C7 [107.8 (2) ], C8-O4-C7-C6 [À170.95 (15) ] and O4-C7-C6-C1 [176.48 (15) ] are typical of the torsional freedom permitted by the rotation of the benzoate group at position 3. The greatest conformational freedom of the molecule resides, therefore, in the benzoate bridge of compound, composed by C8-O4-C7-C6.In the crystal, there are C-HÁ Á Á and C-OÁ Á Á contacts present (Table 1 and Fig. 2) and also --stacking interactions. The HÁ Á Á and OÁ Á Á separations are comparable with those cited by Imai et al. (2008) from a database analysis, which concluded that such interactions were attractive, with interaction energies of ca 2 kcal mol À1 , comparable to those typical of weak hydrogen bonds. These interactions result in the formation of zigzag