Synthesis, magnetic and vibrational properties of two novel mixed-valence iron(II)-iron(III) formate frameworks

Abstract

We report synthesis of two novel mixed-valence iron(II)-iron(III) formate frameworks templated by N-ethylmethylammonium (EtMeA+) and 2-Hydroxyethylammonium (HEA+) cations. X-ray diffraction shows that these compounds crystallize in the P3¯1c niccolite-type structures. Optical studies confirm mixed-valence character of these compounds. Magnetic investigation reveals that both N-ethylmethylammonium iron formate (EtMeAFeFe) and 2-Hydroxyethylammonium iron formate (HEAFeFe) exhibit magnetic order at 36.5 and 37.0K, respectively. EtMeAFeFe also exhibits large negative magnetization below 31.0K indicating that this compound is an N-type ferrimagnet. We also present Raman and IR data for both compounds. In order to help assignment of modes corresponding to the EtMeA+ cation, we also performed quantum chemical calculations to derive the harmonic and anharmonic vibrational wavenumbers. The performed calculations revealed that protonation should affect most strongly modes related to vibrations of the N–H bonds as well as the stretching modes of the CH2 and CH3 groups attached to the N atom.