Effect of Transition Metal Substitution on the Charge-Transfer Phase Transition and Ferromagnetism of Dithiooxalato-Bridged Hetero Metal Complexes, (n-C3H7)4N[FeII1−xMnIIxFeIII(dto)3

Masaya Enomoto,Norimichi Kojima,Atsushi Okazawa,Hiromichi Ida

doi:10.3390/cryst8120446

Abstract

The dithiooxalato-bridged iron mixed-valence complex (n-C3H7)4N[FeIIFeIII(dto)3] (dto = dithiooxalato) undergoes a novel charge-transfer phase transition (CTPT) accompanied by electron transfer between adjacent FeII and FeIII sites. The CTPT influences the ferromagnetic transition temperature according to the change of spin configuration on the iron sites. To reveal the mechanism of the CTPT, we have synthesized the series of metal-substituted complexes (n-C3H7)4N[FeII1-xMnIIxFeIII(dto)3] (x = 0–1) and investigated their physical properties by means of magnetic susceptibility and dielectric constant measurements. With increasing MnII concentration, x, MnII-substituted complexes show the disappearance of CTPT above x = 0.04, while the ferromagnetic phase remains in the whole range of x. These results are quite different from the physical properties of the ZnII-substituted complex, (n-C3H7)4N[FeII1-xZnIIxFeIII(dto)3], which is attributed to the difference of ion radius as well as the spin states of MnII and ZnII.

Highlights

These complexes are composed of a molecular building block of trioxalato-coordinated metal anion, [MIII3 ]3−, and a divalent transition metal ion, exhibiting a two-dimensional (2D) sheet or 3D network structure depending on the size, charge and geometry of the counter cation which acts as a template of the formation of the anionic network [13]
The iron mixed-valence complex (n-C3 H7 )4 N[FeII FeIII3 ] indicates a reversible charge-transfer phase transition (CTPT) with thermal hysteresis at around 120 K, which is induced by electron transfer between adjacent FeII and FeIII sites as shown in Figure 1 [35,36,37]
The result indicates that the MnII ion is not efficiently incorporated into the dto layer compared with the FeII ion, while the ZnII -ion uptake into the layer is significantly preferred to the FeII ion [40,41]

Summary

Introduction

Owing to its versatile bridging modes [1,2,3,4,5,6,7,8,9,10] as well as its remarkable ability to mediate a strong magnetic interaction between paramagnetic metal ions [11], a large number of ox-based coordination compounds with wide ranges of structures and magnetic properties have been reported [12,13] Among these compounds, ox-bridged bimetallic complexes [MII MIII (ox)3 ]− have been a fascinating target for materials chemistry since the discovery of ferromagnetism in the layered complexes (n-C4 H9 ) N[MII CrIII (ox)3 ] (M = Cr, Mn, Fe, Co, Ni, Cu) [14]. The iron mixed-valence complex (n-C3 H7 ) N[FeII FeIII (dto)3 ] indicates a reversible charge-transfer phase transition (CTPT) with thermal hysteresis at around 120 K, which is induced by electron transfer between adjacent FeII and FeIII sites as shown in Figure 1 [35,36,37]

Methods

Results

Conclusion