Crystal structure of Schiff base derivative of 2,2′-dihydroxybiphenyl-3-carbaldehyde with n-butylamine

Abstract

Crystals of the Schiff base derivative of 2,2′-dihydroxybiphenyl-3-carbaldehyde with n-butylamine were examined using X-ray diffraction, FT-IR and CPMAS spectroscopy. Their space group is P- 1 with a=8.377(2), b=12.214(2), c=14.774(3) A ̊ , α=76.62(3)°, β=81.34(3)°, γ=86.62(3)° and Z=4. The unit cell contains two symmetry-independent zwitterions. The hydrogen atom of the protonated N atom of the Schiff base is linked to the oxygen atom of the carbonyl group at position 2, which in turn is linked to the hydroxyl group by a short hydrogen bond [molecule A: N⋯O=2.614(3), O⋯O=2.520(3) Å; molecule B: N⋯O=2.594(4), O⋯O=2.526(3) Å]. The OH⋯O −⋯H +N bifurcated intramolecular hydrogen bonds are crystallographically asymmetric. The results of the FT-IR, 1H, 13C, 15N NMR and CPMAS study of the crystals are in agreement with the X-ray data. Instead of a continuous absorption, only a broad band is found indicating relatively low proton polarizability in the two types of the cooperative relatively short intramolecular hydrogen bonds. The 15N NMR chemical shift indicates the protonation of the Schiff base.