Selected solid-state behaviour of three di-tert-butyl-substituted N-salicylideneaniline derivatives: temperature-induced phase transitions and chromic behaviour

Helen E Mason; Judith A K Howard; Hazel A Sparkes

doi:10.1107/S2053229621008780

Selected solid-state behaviour of three di-tert-butyl-substituted N-salicylideneaniline derivatives: temperature-induced phase transitions and chromic behaviour

Acta Crystallogr C Struct Chem. 2021 Oct 1;77(Pt 10):659-667. doi: 10.1107/S2053229621008780. Epub 2021 Sep 29.

Authors

Helen E Mason¹, Judith A K Howard¹, Hazel A Sparkes²

Affiliations

¹ Department of Chemistry, Durham University, South Road, Durham DH1 3LE, UK.
² School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK.

Abstract

The synthesis, single-crystal structures and chromic behaviour of three related Schiff bases, namely, (E)-2,4-di-tert-butyl-6-{[(4-fluorophenyl)imino]methyl}phenol, C₂₁H₂₆FNO, 1, (E)-2,4-di-tert-butyl-6-{[(4-chlorophenyl)imino]methyl}phenol, C₂₁H₂₆ClNO, 2, and (E)-6-{[(4-bromophenyl)imino]methyl}-2,4-di-tert-butylphenol, C₂₁H₂₆BrNO, 3, are reported. Two polymorphs of 1 were obtained, which were found to have different photochromic properties. Schiff bases 2 and 3 were found to be isostructural and underwent a phase transition upon cooling which was attributed to the dynamic disorder in one of the tert-butyl groups resolving at low temperature. All of the structures were found to exist in the enol rather than the keto form based on the C-O(H) and imine C=N bond lengths, and contained an intramolecular O-H...N hydrogen bond alongside weaker intermolecular C-H...O contacts.

Keywords: Schiff base; chromism; crystal structure; phase transition; polymorphism.

open access.