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...

A linear metal–metal bonded tri-iron single-molecule magnet

“…Notably, the fit was not significantly improved by incorporating a rhombic ZFS parameter or intermolecular interactions in the model and degraded strongly upon forcing D to be positive. The estimated FM interaction in [Fe 3 (DpyF) 4 ](BF 4 ) 2 2CH 3 CN (J/k B = +20.9 K) is slightly larger than in Fe 4 (tpda) 3 X 2 (J/k B = +10.1 to +15.4 K), 12,13 which possess longer Fe-Fe distances (> 2.9 Å vs. 2.78 Å).…”

“…Recently, a trinuclear compound with three bridging 2,6bis[(trimethylsilyl)amido]pyridine ligands was obtained with FM coupling between the Fe II centers (2.442 Å). 11 Additionally, the tetranuclear complexes Fe 4 (tpda) 3 Cl 2 12 and Fe 4 (tpda) 3 Br 2 , 13 with mixed bridging-chelating tripyridyldiamido modes and long Fe-Fe distances of > 2.9 Å, were modelled as consisting of two FM coupled Fe 2 pairs, with antiferro-magnetic (AF) inter-pair interactions. In 1998, a tri-iron cluster with a similar mixed coordination mode, [Fe 3 (DpyF) 4 ](PF 6 ) 2 , (DpyF = dipyridylformamide), was reported to have a room-temperature T value of 16 cm 3 K mol −1 , much higher than that expected for three isolated Fe II centers, once again suggesting FM coupling between the Fe II spins.…”

The First Tetranuclear Iron(II)‐Gadolinium(III) Carboxylate Complex [Fe2Gd2(piv)10(bpy)2]: Synthesis, Structure Elucidation and Magnetic Properties

“…[46,47] Based on the analysis carried out in the SHAPE 2.1 program, [48] the coordination environment of Fe(1) (FeO 4 N 2 ) can be described as a strongly distorted octahedron, while the environment of the Gd(1) (GdO 7 ) (Figure 2, Figure S2) -as a capped trigonal prism, where the agreement factor describing the deviation extent from an ideal triangular dodecahedron is ChemistrySelect equal to 2.193(2) and 2.148(2) Å, that is characteristic of highspin iron(II) species. [9,49] The packing of molecules 1 in the crystal is stabilized by CÀ H⋅⋅⋅O interactions (Table S1, Figure S3) between hydrogen atoms of bpy molecules, piv-anions, and oxygen atoms of coordinated carboxylic groups with supramolecular chains formation directed along the axis a. The tetranuclear molecules of 1 are isolated in the crystal cell by the peripheral tert-butyl and 2,2'-bipyridine groups (Figure 3).…”

Metal–Metal-Bonded Fe4 Clusters with Slow Magnetic Relaxation

“…Transition metal clusters featuring direct metal–metal orbital overlap are emerging as a new class of single-molecule magnets (SMMs). , The metal–metal bonding present in these clusters can result in ferromagnetic (direct) exchange interactions and energetically isolated magnetic ground states, − often leading to complexes with high relaxation barriers and long-lived magnetization. ,− For example, [Bu 4 N]­[( H L) 2 Fe 6 (py) 2 ] [ H LH 6 = MeC­(CH 2 NHPh- o -NH 2 ) 3 ] features an S = 19/2 ground state and a relaxation barrier of U eff = 42.5(8) cm –1 . This cluster exhibits an octahedral arrangement of six Fe atoms, with relatively short Fe–Fe bonds (ca.…”

“…Like [Bu 4 N]­[( H L) 2 Fe 6 (py) 2 ], this cluster features a compact metal core with short Co–Co bonds (2.36 Å), which leads to slow magnetic relaxation. The Fe­(II) chain clusters [Fe 4 (tpda) 3 X 2 ] [H 2 tpda = N , N -bis­(pyridin-2-yl)­pyridine-2,6-diamine; X = Cl, Br] and [Fe 3 (DpyF) 4 ]­[BF 4 ] 2 (DpyF = dipyridylformamide) also exhibit ferromagnetic exchange and slow magnetic relaxation, − although in these examples, the Fe–Fe distances are relatively long (>2.8 Å). Several other Fe–Fe-bonded complexes also feature high-spin ground states as a consequence of direct exchange interactions, including [Na 6 Fe 3 (tris- cyclo -salophen)­(py) 9 ], [Fe­( i PrNPPh 2 ) 3 Fe­(PMe 3 )], [Fe 2 (DPhF) 3 ], and [Fe 2 (DPhF) 4 ] (DPhF = diphenylforamidinate). − Although the magnetic relaxation in these examples was not explicitly measured, the observation that direct M–M bonding can lead to ferromagnetic exchange further highlights the value of this design feature.…”