Crystal structures and antioxidant capacity of (E)-5-benzyloxy-2-{[(4-chlorophenyl)imino]methyl}phenol and (E)-5-benzyloxy-2-({[2-(1H-indol-3-yl)ethyl]iminiumyl}methyl)phenolate

Abstract

The title Schiff base compounds, C20H16ClNO2 (I) and C24H22N2O2 (II), were synthesized via the condensation reaction of 2-amino-4-chlorophenol for (I), and 2-(2,3-dihydro-1H-indol-3-yl)ethan-1-amine for (II), with 4-benzyloxy-2-hydroxybenzaldehyde. In both compounds, the configuration about the C=N imine bond is E. Neither molecule is planar. In (I), the central benzene ring makes dihedral angles of 49.91 (12) and 53.52 (11)° with the outer phenyl and chlorophenyl rings, respectively. In (II), the central benzene ring makes dihedral angles of 89.59 (9) and 72.27 (7)°, respectively, with the outer phenyl ring and the mean plane of the indole ring system (r.m.s. deviation = 0.011 Å). In both compounds there is an intramolecular hydrogen bond forming an S(6) ring motif; an O—H...O hydrogen bond in (I), but a charge-assisted N+—H...O− hydrogen bond in (II). In the crystal of (I), molecules are linked by C—H...π interactions, forming slabs parallel to plane (001). In the crystal of (II), molecules are linked by pairs of N—H...O hydrogen bonds, forming inversion dimers. The dimers are linked by C—H...O hydrogen bonds, C—H...π interactions and a weak N—H...π interaction, forming columns propagating along the a-axis direction. The antioxidant capacity of the synthesized compounds was determined by cupric reducing antioxidant capacity (CUPRAC) for compound (I) and by 2,2-picrylhydrazyl hydrate (DPPH) for compound (II).

Keywords

• crystal structure
• Schiff base
• DPPH
• CUPRAC
• antioxidant capacity
• charge-assisted hydrogen bonding
• X—H...π interactions