Towards ionic liquids with tailored magnetic properties: bmim+ salts of ferro- and antiferromagnetic Cu3II triangles

Complexes (bmim)(2)[Cu-3(mu(3)-Cl)(2)(mu-pz)(3)Cl-3] (1), (bmim)[Cu-3(mu(3)-OH)(mu-pz)(3)Cl-3] (2) and (bmim)(2)[Cu-3(mu(3)-OH) (mu-Cl)(mu-pz)(3)Cl-3] (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 ferro-magnetic interactions for 1 with small magnetoanisotropy in its ground state (D-3/2 similar to 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 degrees C for 1, which is lower than that of its PPN+ and Bu4N+ analogues (1PPN and 1Bu(4)N, respectively, PPN+ = bis(triphenylphosphine) iminium). Upon cooling, 1 remains molten down to 70 degrees C. Mixtures of the salts 1, 1PPN and 1Bu(4)N, exhibited modified melting behaviours, with the mixtures exhibiting lower melting points than those of either of their pure components.