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

Complexes (bmim)[Cu(μ-Cl)(μ-pz)Cl] (1), (bmim)[Cu(μ-OH)(μ-pz)Cl] (2) and (bmim)[Cu(μ-OH)(μ-Cl)(μ-pz)Cl] (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∼ 10 cm) and intramolecular antiferromagnetic interactions for 2 and 3 (-285 and -98 cm 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 BuN analogues (1PPN and 1BuN, respectively, PPN = bis(triphenylphosphine)iminium). Upon cooling, 1 remains molten down to 70 °C. Mixtures of the salts 1, 1PPN and 1BuN, exhibited modified melting behaviours, with the mixtures exhibiting lower melting points than those of either of their pure components.