Synthesis, structure and magnetic properties of Nd3+ and Pr3+ 2D polymers with tetrafluoro-p-phthalate

Abstract

Two lanthanide tetrafluoro-p-phthalate (L²⁻) complexes, Ln(L)_1.5·DMF·H₂O (Ln = Pr³⁺ (1), Nd³⁺ (2)), were synthesized using pyridine as a base. The compounds were found to be isostructural, and the structure of 1 has been determined by single crystal X-ray diffraction (monoclinic, space group C2, a = 22.194(2) Å, b = 11.4347(12) Å, c = 11.7160(12) Å, β = 94.703(2)°, V = 2963.3(5) ų, Z = 4). The crystal structure of 1 consists of dinuclear Pr³⁺ units, which are connected by tetrafluoro-p-phthalate, forming separate 2D polymeric layers. The Ln³⁺ ions in the dinuclear Ln₂ units are linked by two μ-O atoms and by two bridging O-C-O groups. The structure is porous with DMF and water molecules located between layers. Non-coordinated DMF molecules occupy about 27% of the unit cell volume. A systematic analysis of reported structures of Ln(III) polymers with p-phthalate and its derivatives shows that the ca. known 60 structures can be divided into six possible structural types depending on the presence of certain structural motifs. The magnetic properties of compounds 1 and 2 were studied. The dependence of χ_MT on T (where χ_M is magnetic susceptibility per dinuclear lanthanide unit) for 1 and 2 was simulated using two different models, based on: (i) the Hamiltonian Ĥ = ΔĴ_z²+ μ_Bg_JHĴ, which utilises an axial splitting parameter Δ and temperature-independent paramagnetism (tip) and (ii) crystal field splitting. It was found that both models gave satisfactory fits, indicating that the Ln–Ln exchange interactions are small and the symmetry of the coordination environment is the main factor influencing the magnetic properties of these compounds.