Towards ionic liquids with tailored magnetic properties: bmim+ salts of ferro- and antiferromagnetic Cu II3 triangles

Abstract

Complexes (bmim)₂[Cu₃(μ₃-Cl)₂(μ-pz)₃Cl₃] (1), (bmim)[Cu₃(μ₃-OH)(μ-pz)₃Cl₃] (2) and (bmim)₂[Cu₃(μ₃-OH)(μ-Cl)(μ-pz)₃Cl₃] (3) were synthesized (bmim⁺ = 1-butyl-3-methylimidazolium, pz⁻ = pyrazolato anion). Dianionic complexes 1 and 3 were obtained as crystalline solids, whereas the monoanionic complex 2 was obtained as a viscous paste. Magnetic susceptibility and X-band EPR studies revealed intramolecular ferromagnetic interactions for 1 with small magnetoanisotropy in its ground state (D_3/2 ∼ 10⁻³ cm⁻¹) and intramolecular antiferromagnetic interactions for 2 and 3 (−285 and −98 cm⁻¹ average J, respectively) with important magnetic anisotropy in their ground states stemming from a combination of low magnetic symmetry and antisymmetric exchange interactions. Thermal studies revealed a clear melting point of 140 °C for 1, which is lower than that of its PPN⁺ and Bu₄N⁺ analogues (1PPN and 1Bu₄N, respectively, PPN⁺ = bis(triphenylphosphine)iminium). Upon cooling, 1 remains molten down to 70 °C. Mixtures of the salts 1, 1PPN and 1Bu₄N, exhibited modified melting behaviours, with the mixtures exhibiting lower melting points than those of either of their pure components.