New properties of the [3-MeRad]2[Mn2{Cu(opba)}3] system [3-MeRad+=radical cation, opba=ortho-phenylenebis(oxamato)]: a molecule-based magnet with two-dimensional behavior

Three compounds have been synthesized, the formulae of which are [3-MeRad]2[Cu(opba)]·4H2O (1), [3-MeRad]2[Mn2{Cu(opba)}3]·6DMSO·8H2O (2), and [3-MeRad]2[Mn2{Cu(opba)}3]·3DMSO·2.5H2O (3), where opba is ortho-phenylenebis(oxamato) and 3-MeRad+ is 2-(3-N-methyl-pyridinium)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide. Their magnetic properties have been investigated in the 1.8–300 K temperature range. By reaction of 1 and MnCl2·3H2O in DMSO, small crystals of 2 were obtained. Single crystal X-ray analysis was employed to determine the lattice parameters for 2: a=15.9(2); b=17.8(2); c=18.0(3) Å; α=γ=90(1); β=114(1)°. The temperature dependence of the magnetic susceptibility in the form of the χMT versus T plot reveals a typical ferrimagnetic behavior for 2, although the low field FC and ZFC curves show an antiferromagnetic-like interaction below 13 K. Above 200 Oe this interaction disappears as in weak metamagnets. With a thermal-vacuum treatment applied to 2, solvent molecules are removed affording 3 which presents long-range order around 15 K. The results indicate that the bimetallic compounds present a structure consisting of two-dimensional honeycomb-like networks without interlocking of the M6Cu6 hexagons.