The first example of coexistence of the ketoamino-enolimino forms of diamine Schiff base naphthaldimine parts:: the crystal and molecular structure of N,N′-bis(1-naphthaldimine)-o-phenylenediamine chloroform (1/1) solvate at 200 K

The N,N-1-bis(1-naphthaldimine)-o-phenylenediamine chloroform (1/1) solvate was prepared from 2-hydroxy-1-naphthaldehyde and 1,2-phenylenediamine in a 2:1 molar ratio and characterized in solution and in the solid state using X-ray single crystal diffractometry, IR and NMR spectroscopy. The structure consists of three structural fragments: two planar, but not coplanar naphthaldimine moieties linked by phenyl ring that derived from o-phenylenediamine. The naphthaldimine fragments contain, along with naphthalene rings, six-membered pseudoaromatic chelate rings, formed by O-(HN)-N-... or N-(HO)-O-... intramolecular hydrogen bonds that retain planarity of the aldimine fragments. This structure is the first example of the coexistence of two different hydrogen bond types within Schiff base molecule, i.e. the one naphthaldimine part exists in the enolimino form (O-(HN)-N-... hydrogen bond of 2.5487(17) Angstrom), while the other exists in the ketoamino form (N-(HO)-O-... hydrogen bond of 2.5706(19) Angstrom). The different hydrogen bond types are related to the different pi electron density distribution within two parts. The amino hydrogen atom forms three-center intramolecular hydrogen bond, which includes the N-(HO)-O-... hydrogen bond of 2.5706(19) Angstrom within the ketoamino part and also the N-(HN)-N-... bond of 2.7238(18) A linking two naphthaldimine fragments of the molecule. IR and H-1 and C-13 NMR spectral data are consistent with revealed molecular structure in the solid state. (C) 2001 Elsevier Science B.V. All rights reserved.