Magnetic properties of two GdIIIFeIII4 metallacrowns and strategies for optimizing the magnetocaloric effect of this topology

Abstract

Two Gd^III Fe^III4 metallacrown complexes are presented and analyzed for their magnetic properties. One of these species is newly identified and exhibits a bent ring geometry as opposed to the more conventional flatter conformation of the other. Both complexes are quite similar magnetically, exhibiting antiferromagnetic exchange coupling values ca. J(Fe^III–N–O–Fe^III) = −7 cm⁻¹ and J(Gd^III–O–Fe^III) = −0.7 cm⁻¹. When analyzed for the molecular magnetocaloric effect, maximum −ΔS_m values of 7.3 J K⁻¹ kg⁻¹ at 3 K and at 6.1 J K⁻¹ kg⁻¹ at 4 K were exhibited. A detailed structural-magnetic correlation is established and an assessment of several similar magnetic metallacrowns with diverse metal combinations is given with regards to their potential magnetocaloric properties. Strategies for improving the magnetocaloric properties within the Metaln + FeIII4 family of metallacrowns are proposed regarding the ratio between coupling parameters J(Fe^III–N–O–Fe^III)/J(Metalⁿ⁺–O–Fe^III).