pi-electron delocalisation in the spacer of the O-H...N bridge in Schiff bases. Crystal and molecular structure of 3,5-dimethoxy-2[(phenylimino)methyl]phenol and 4-methoxy-2-[(phenylimino)methyl]phenol.

The spacer built up of N=C, two CC, and CO bonds between the H-bond donatin g OH group and H-bond accepting nitrogen atom in the C=N bond in Schiff bas es exhibits a significant and strongly diversified degree of the pi-electro n delocalisation. No dependence between the delocalisation of pi electrons and the H-bond strength is observed The most important factor appears to be the mesomeric effect of the substituents attached to the ring of which a b ond is a part of the spacer. This is supported by analysis of the geometry of 3,5-dimethoxy-2[(phenylimino) methyl] phenol and 4-methoxy-2-[(phenylimi no) methyl] phenol presented in this study and molecular geometries of 47 w ell solved X-ray structures retrieved from the CSD. (C) 1999 Elsevier Scien ce Ltd. All rights reserved.