Hydrogen bonding properties and intermediate structure of N-(2-carboxyphenyl)salicylidenimine

The hydrogen bonding properties, the nature of the tautomeric structure and dimerization of N-(2-carboxyphenyl)-salicylidenimine 1 has been studied, T he crystal and molecular structure of 1 has been determined by single-cryst al X-ray diffraction analysis. This compound forms a dimer in the solid sta te, which is held together by two strong intermolecular O-H O bridges [O(1) O(2a) = 2.455(1) Angstrom]. This dimeric structure is further stabilized b y two intramolecular N-H O hydrogen bonds [N(1) O(1)= 2.654(1) and N(1)1 O( 2)2 2.663(1) Angstrom]. In this way, an eight-membered pseudocycle is creat ed. However, in methanol or acetonitrile solution, no dimerization was obse rved according to H-1-NMR, IR and UV measurements. It was also found that t his compound exists as an intermediate form between a phenol-imine and an o -quinoid structure. In addition, a derivative soluble in chloroform, 2-[2-h ydroxy-5-(2-butyl)benzylideneamino benzoic acid 3, was examined for compari son.