Anisotropic exchange interactions in [LnFe] dinuclear systems: Magnetometry, dual mode X-band Electron Paramagnetic Resonance, and Mössbauer spectroscopic studies

An experimental and theoretical procedure is introduced in order to calculate the magnitude and anisotropy of interaction between a lanthanide and a 3d-metal ion. The general formula of the molecular compounds is [Ln(H₂O)₃(dmf)₄(μ-CN)Fe-(CN) ₅] · nH₂O, where 1 ≤ n ≤ 1,5 and dmf = N,N′-dimethylformamide, abbreviated as [LnFe] from now on. The main parts of this procedure are (a) the evaluation of the effective g-parameters of the lanthanide ion with the help of EPR measurements; (b) the use of dual-mode EPR spectroscopy to define the anisotropic exchange interactions with the help of an anisotropic Hamiltonian model; (c) use of the same magnetic model to fit magnetization and susceptibility data in order to verify the EPR findings; and (d) introduction of a supportive technique, in our case Mössbauer spectroscopy due to the presence of the Fe ion. It was possible to define some trends concerning the exchange components of the [CeFe] dimer according to which the isotropic exchange constant is smaller than 2 cm^-1 and the anisotropic components are [D, E] = [0.06(1), 0.05(1)] cm^-1. Using EPR spectrosopy it was possible to prove that the [PrFe] and [EuFe] dimers have negligible interactions. For the case of [PrFe], using appropriate magnetic models the energy difference between the ground state Γ₁ and the excited Γ₃, Γ₄ and Γ₅ were calculated and found to be Δ₃₁ = 293(5) cm^-1, Δ₄₁ = 76(5) cm^-1 and Δ₅₁ = 232(5) cm^-1. For the case of [EuFe], the spin-orbit coupling parameter was found to be λ = 340 cm^-1.