Abrupt Spin Crossover Behavior in a Linear N1,N2-Triazole Bridged Trinuclear Fe(II) Complex

Ai-Min Li,Eva Rentschler,Volker Schünemann,Juliusz Wolny,Tim Hochdörffer

doi:10.3390/magnetochemistry4030034

Abstract

The synthesis, structures and magnetic properties of a new trinuclear spin crossover complex [FeII3(pyrtrz)6(TsO)6]·10H2O·2CH3OH (C2) and its analogue binuclear [FeII2(pyrtrz)5(SCN)4]·7H2O (C1), are reported here. These two compounds are synthesized based on the pyrrolyl functionalized Schiff base 1,2,4-triazole ligand 4-((1H-pyrrol-2-yl)methylene-amino)-4H-1,2,4-triazole (pyrtrz), which represent rare discrete multi-nuclear species, with µ2-N1,N2-triazole bridges linking the FeII centers. DC magnetic susceptibility measurements revealed an abrupt single-step spin crossover (SCO) behavior for compound 2 on the central FeII site and single-crystal X-ray diffraction (173 K) showed that this compound crystallizes in the monoclinic space group (P21/c), and multiple intramolecular interactions were found responsible for the abrupt transition. Compound 1 is a binuclear complex with thiocyanate as terminal ligands. This compound stays in high spin state over the whole temperature range and displays weak antiferromagnetic exchange coupling.

Highlights

spin crossover (SCO) as a phenomenon of molecular bistability can mainly be observed in first row transition metal complexes with a d4–d7 electron configuration in octahedral ligand geometry
We could enlarge the family of binuclear systems showing multiple SCO steps with reports on thiadiazole and oxadiazole complexes for which the cooperativity was studied in detail [9,10]
Similar to these discrete SCO systems, low nuclearity complexes based on the more simple triazole ligand, i.e., binuclear and trinuclear complexes triple-bridged by N1,N2-1,2,4-triazole ligands, are currently receiving great interest [11,12,13,14,15]

Summary

Introduction

SCO as a phenomenon of molecular bistability can mainly be observed in first row transition metal complexes with a d4–d7 electron configuration in octahedral ligand geometry. We could enlarge the family of binuclear systems showing multiple SCO steps with reports on thiadiazole and oxadiazole complexes for which the cooperativity was studied in detail [9,10] Similar to these discrete SCO systems, low nuclearity complexes based on the more simple triazole ligand, i.e., binuclear and trinuclear complexes triple-bridged by N1,N2-1,2,4-triazole ligands, are currently receiving great interest [11,12,13,14,15]. Multiple intramolecular interactions were found being responsible for the sharp transition

General Methods and Materials

Single Crystal X-ray Diffraction

X-ray Crystal Structure Description

Magnetic Susceptibility and Mössbauer Spectroscopy

Conclusions