Broad spin crossover in an iron( iii ) Schiff base complex with a cis-FeN$_4$O$_2$ coordination environment

Asymmetrical condensation of ethylenediamine with 5-bromo-2-hydroxybenzaldehyde yielded a Schiff base, (E)-2-(((2-aminoethyl)imino)methyl)-4-bromophenol (5-Brsaen), and the reaction with Fe(NO$_3$)$_3$·9H$_2$O generated the complex [Fe(5-Brsaen)$_2$]NO$_3$·CH$_3$OH (1). The complex was characterised by single crystal XRD measurements, elemental analysis, FT-IR spectra, DC magnetic susceptibility measurements and variable temperature Mössbauer spectroscopy. The single crystal XRD studies of 1 at 293 K and 173 K reveal that the Fe–N and Fe–O bond lengths are intermediate between what would be expected for HS and LS Fe(III). The hydrogen bonds result in a 2D supramolecular structure. DC magnetic measurements between 300 and 2 K reveal that the compound does not reach a pure HS state even at RT. Furthermore, the proportion of HS to LS decreases as the temperature decreases and reaches a LS state at 2 K. Variable temperature Mössbauer spectra are in line with this conclusion.