Spin Cross-Over (SCO) Complex Based on Unsymmetrical Functionalized Triazacyclononane Ligand: Structural Characterization and Magnetic Properties

Merzouk Halit,Véronique Patinec,Smail Triki,Mélissa Roger,Carlos Gómez-García,Said Yefsah

doi:10.3390/magnetochemistry5010019

Abstract

The unsymmetrical ligand 1-(2-aminophenyl)-4,7-bis(pyridin-2-ylmethyl)-1,4,7-triazacyclononane (L6) has been prepared and characterized by NMR spectroscopy. The L6 ligand is based on the triazamacrocycle (tacn) ring that is functionalized by two flexible 2-pyridylmethyl and one rigid 2-aminophenyl groups. Reaction of this ligand with Fe(ClO4)2·xH2O led to the complex [Fe(L6)](ClO4)2 (1), which was characterized as the first Fe(II) complex based on the unsymmetrical N-functionalized tacn ligand. The crystal structure revealed a discrete monomeric [FeL6]2+ entity in which the unsymmetrical N-functionalized triazacyclononane molecule (L6) acts as hexadentate ligand. As observed in the few parent examples that are based on the symmetrical N-functionalized tacn ligands, the triazacyclononane ring is facially coordinated and the N-donor atoms of the three functional groups (two pyridine and one aniline groups) are disposed in the same side of the tacn ring, leading to a distorted FeN6 environment. The magnetic studies of 1 revealed the presence of an incomplete spin crossover (SCO) transition above 425 K, whose progress would be prevented by a very exothermic thermal decomposition at ca. 472 K, as shown by thermogravimetric and DSC measurements.

Highlights

Among the molecular switchable materials, the spin crossover (SCO) complexes are undoubtedly the most studied ones during the last decade, because of their several potential applications, including memory display devices [1–21]
We report the synthesis of 1-(2-aminophenyl)-4,7-bis(pyridin-2-ylmethyl)-1,4,7-triazacyclononane (L6 in Scheme 1), as well as that of the corresponding Fe(II) ion (Fe)(II) complex [FeL6](ClO4)[2] (1)
1,4-bis(pyridin-2-ylmethyl)-1,4,7-triazacyclononane (A) was synthesized, starting from the triazamacrocycle ligand following the known orthoamide route that is already used for producing unsymmetrical N-functionalized tacn [55,61,62]

Summary

Introduction

Among the molecular switchable materials, the spin crossover (SCO) complexes are undoubtedly the most studied ones during the last decade, because of their several potential applications, including memory display devices [1–21]. In view of the above observations, even if only based on two reports, such functionalized triazamacrocycle ligands appear as interesting ligands to design SCO materials with transition temperatures around or above room temperature, and more examples are needed to establish correlations between the magnetic coupling and the structural parameters, and to obtain more structural data on structural features of both HS and LS states, which are essential in shedding light on the effect of the nature of the functional groups and/or the unsymmetrical character of the functionalized ligand on the SCO characteristics In this context, we have designed a series of unsymmetrical N-functionalized triazacyclononane involving two different groups, such as the examples depicted in Scheme 1 (L6 and L7). We report their spectroscopic and structural characterizations and the magnetic properties of the iron (II) complex 1

Synthesis

Description of the Structure

Starting Materials

Crystallographic Data Collection and Refinement

Conclusions