title: The zwitterionic structure of 2-hydroxy-4-[(2-hydroxybenzylidene)amino]benzoic acid.
abstract: The title compound, C₁₄H₁₁NO₄, exists in the solid phase in the zwitterionic form, 2-{[(4-carboxy-3-hydroxyphenyl)iminiumyl]methyl}phenolate, with the H atom from the phenol group on the 2-hydroxybenzylidene ring transferred to the imine N atom, resulting in a strong intramolecular N-H∙∙∙O hydrogen bond between the iminium H atom and the phenolate O atom, forming a six-membered hydrogen-bonded ring. In addition, there is an intramolecular O-H∙∙∙O hydrogen bond between the carboxylic acid group and the adjacent hydroxy group of the other ring, and an intermolecular C-H∙∙∙O contact involving the phenol group and the C-H group adjacent to the imine bond, connecting the molecules into a two-dimensional network in the (103) plane. π-π stacking interactions result in a three-dimensional network. This study is important because it provides crystallographic evidence, supported by IR data, for the iminium zwitterionic form of Schiff bases.
authors.affiliation: Department of Chemistry, Federal University of Juiz de Fora, Juiz de Fora, Minas Gerais 36036-900, Brazil.
authors.forename: Anderson A B C
authors.initials: AA
authors.lastname: Júnior
authors.forename: Gustavo S G
authors.initials: GS
authors.lastname: De Carvalho
authors.forename: Lippy F
authors.initials: LF
authors.lastname: Marques
authors.forename: Charlane C
authors.initials: CC
authors.lastname: Corrêa
authors.forename: Adilson D
authors.initials: AD
authors.lastname: Da Silva
authors.forename: Flávia C
authors.initials: FC
authors.lastname: Machado
keywords: Schiff bases; carboxylic acids; crystal structure; zwitterionic structures