Tetranuclear Hetero-Metal [Co^II₂Ln^III₂] (Ln = Gd, Tb, Dy, Ho, La) Complexes Involving Carboxylato Bridges in a Rare μ₄–η²:η² Mode: Synthesis, Crystal Structures, and Magnetic Properties

Abstract

A new family of 3d-4f heterometal 2 × 2 complexes [Co(II)2(L)2(PhCOO)2Ln(III)2(hfac)4] (1-5) (Ln = Gd (compound 1), Tb (compound 2), Dy (compound 3), Ho (compound 4), and La (compound 5)) have been synthesized in moderate yields (48-63%) following a single-pot protocol using stoichiometric amounts (1:1 mol ratio) of [Co(II)(H2L)(PhCOO)2] (H2L = N,N'-dimethyl-N,N'-bis(2-hydroxy-3,5-dimethylbenzyl)ethylenediamine) as a metalloligand and [Ln(III)(hfac)3(H2O)2] (Hhfac = hexafluoroacetylacetone) as a lanthanide precursor compound. Also reported with this series is the Zn-Dy analog [Zn(II)2(L)2(PhCOO)2Dy(III)2(hfac)4] 6 to help us in understanding the magnetic properties of these compounds. The compounds 1-6 are isostructural. Both hexafluoroacetylacetonate and benzoate play crucial roles in these structures as coligands in generating a tetranuclear core of high thermodynamic stability through a self-assembly process. The metal centers are arranged alternately at the four corners of this rhombic core, and the carboxylato oxygen atoms of each benzoate moiety bind all of the four metal centers of this core in a rare μ4-η(2):η(2) bridging mode as confirmed by X-ray crystallography. The magnetic susceptibility and magnetization data confirm a paramagnetic behavior, and no remnant magnetization exists in any of these compounds at vanishing magnetic field. The metal centers are coupled in an antiferromagnetic manner in these compounds. The [Co(II)2Dy(III)2] compound exhibits a slow magnetic relaxation below 6 K, as proven by the AC susceptibility measurements; the activation energy reads U/kB = 8.8 K (τ0 = 2.0 × 10(-7) s) at BDC = 0, and U/kB = 7.8 K (τ0 = 3.9 × 10(-7) s) at BDC = 0.1 T. The [Zn(II)2Dy(III)2] compound also behaves as a single-molecule magnet with U/kB = 47.9 K and τ0 = 2.75 × 10(-7) s.

Construction of lanthanide complexes supported by 2,3‐dimethoxybenzoic acid and 5,5’‐dimethy‐2,2’‐bipyridine: crystal structures, thermoanalysis, magnetic and fluorescence properties

“…For photoluminescence, rare‐earth ions are usually used as luminescent centers for their high luminescence efficiency and adjustable emission color . Rare earth ions have magnetic anisotropy in magnetism, which makes them often used to make molecular‐based magnetic materials, such as single‐molecule magnets (SMMs) and single‐chain magnets (SCMs) . Not only that, rare‐earth ions are also used in other fields, such as bioassays, biological labels, light‐converting optical materials luminescent probes and light emitting diodes .…”

Chloride‐Selective Electrodes Based on “Two‐Wall” Aryl‐Extended Calix[4]Pyrroles: Combining Hydrogen Bonds and Anion–π Interactions to Achieve Optimum Performance

“…In recent years, incorporation of 3d and 4f metal ions into a discrete cluster has been demonstrated to be a promising way to construct SMMs because of not only the ferromagnetic coupling between 3d and heavy 4f metal ions but also the large spin ground state and uniaxial magnetic anisotropic nature of Ln 3+ ions (such as Tb 3+ and Dy 3+ ) 8,9. Up to now, a variety of 3d–4f SMMs, containing Cu‐ Ln ,10 Co‐ Ln ,11 Fe‐ Ln ,12 and Mn‐ Ln ,13 clusters, have been reported, however, the number is still limited due to the inherent difficulties encountered during their preparation 14…”

Systematic Investigation of Reaction‐Time Dependence of Three Series of Copper–Lanthanide/Lanthanide Coordination Polymers: Syntheses, Structures, Photoluminescence, and Magnetism

“…An optimum external DC fieldo f3 000 Oe was appliedt o reduce the quantum tunneling effect. [26] As ar esult, peak values of the out-of-phases ignals for 9a and 9b were realized (Figures 8a nd 9). Based on these peak values, the relaxation parameters of 9a and 9b were analyzed by the Arrhenius equation, providing effective energyb arriers (U eff )o f5 1.7 and 36.5 Ka sw ell as pre-exponential factors (t 0 )o f2 .2 10 À7 and 2.6 10 À9 sf or 9a and 9b,r espectively (Figures 8a nd 9, insets).…”