Two mononuclear iron(ii) complexes of 4-phenylpyrazole-5-carbaldehyde derived ligands are stabilised in different spin states

Abstract

The polydentate acyclic ligand 4-phenylpyrazole-5-carbaldehyde azine, H 2L 1, has been prepared and characterised. A second 4-phenylpyrazole-5-carbaldehyde derived ligand, H 2L 2, was prepared in situ by condensation with o-phenylendiamine. Two mononuclear iron(ii) complexes, [Fe II(HL 2)(MeOH)(NCSe)]·H 2O and [Fe II(H 2L 1) 2](BF 4) 2·solvents, have been synthesised from 1:1 and 2:3 M:L reactions, respectively. No dinuclear, helical, species were obtained from 2:3 M:L reactions regardless of the solvent employed (MeOH, MeCN or NO 2Me). An X-ray structure determination on the latter complex reveals that it is low spin at 90 K. Mössbauer spectra confirm this, and show that the former complex ..