Issue 22, 2021

Tetrairon(ii) extended metal atom chains as single-molecule magnets

Abstract

Iron-based extended metal atom chains (EMACs) are potentially high-spin molecules with axial magnetic anisotropy and thus candidate single-molecule magnets (SMMs). We herein compare the tetrairon(II), halide-capped complexes [Fe4(tpda)3Cl2] (1Cl) and [Fe4(tpda)3Br2] (1Br), obtained by reacting iron(II) dihalides with [Fe2(Mes)4] and N2,N6-di(pyridin-2-yl)pyridine-2,6-diamine (H2tpda) in toluene, under strictly anhydrous and anaerobic conditions (HMes = mesitylene). Detailed structural, electrochemical and Mössbauer data are presented along with direct-current (DC) and alternating-current (AC) magnetic characterizations. DC measurements revealed similar static magnetic properties for the two derivatives, with χMT at room temperature above that for independent spin carriers, but much lower at low temperature. The electronic structure of the iron(II) ions in each derivative was explored by ab initio (CASSCF-NEVPT2-SO) calculations, which showed that the main magnetic axis of all metals is directed close to the axis of the chain. The outer metals, Fe1 and Fe4, have an easy-axis magnetic anisotropy (D = −11 to −19 cm−1, |E/D| = 0.05–0.18), while the internal metals, Fe2 and Fe3, possess weaker hard-axis anisotropy (D = 8–10 cm−1, |E/D| = 0.06–0.21). These single-ion parameters were held constant in the fitting of DC magnetic data, which revealed ferromagnetic Fe1–Fe2 and Fe3–Fe4 interactions and antiferromagnetic Fe2–Fe3 coupling. The competition between super-exchange interactions and the large, noncollinear anisotropies at metal sites results in a weakly magnetic non-Kramers doublet ground state. This explains the SMM behavior displayed by both derivatives in the AC susceptibility data, with slow magnetic relaxation in 1Br being observable even in zero static field.

Graphical abstract: Tetrairon(ii) extended metal atom chains as single-molecule magnets

Supplementary files

Article information

Article type
Paper
Submitted
26 Mac 2021
Accepted
03 Mei 2021
First published
03 Mei 2021

Dalton Trans., 2021,50, 7571-7589

Author version available

Tetrairon(II) extended metal atom chains as single-molecule magnets

A. Nicolini, M. Affronte, D. J. SantaLucia, M. Borsari, B. Cahier, M. Caleffi, A. Ranieri, J. F. Berry and A. Cornia, Dalton Trans., 2021, 50, 7571 DOI: 10.1039/D1DT01007G

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