Ferromagnetism in an extended three-dimensional, diamond-like copper(II) network: A new copper(II)/1-hydroxybenzotriazolato complex exhibiting soft-magnet properties and two transitions at 6.4 and 4.4 K

The use of the substituted benzotriazole ligand btaOH (1-hydroxybenzotriazole) in copper(II) chemistry has yielded a structurally and magnetically very interesting complex. The [Cu-2(O2CMe)(4)(H2O)(2)]/btaOH.H2O/aqueous NH3 (1:4:4, 1.3:3, 1:2:2) reaction system in MeOH gives dark brown-green [Cu(btaO)(2)(MeOH)](n) (4) in similar to 80% yield. 4 crystallizes in the tetragonal space group P4(3)2(1)2 with (at 25 degrees C) a = 9.915(1) Angstrom, b = 9.915(1) Angstrom, c = 14.715(2) Angstrom, and Z = 4. The structure consists of a 3D, diamond-like copper(II) lattice. The Cu-II atom has a square pyramidal geometry with four btaO(-) ligands at the basal plane. The btaO(-) ion functions as a bidentate bridging ligand, with N(3) and the deprotonated oxygen being the ligating atoms. Dc and ac magnetic susceptibility measurements, together with low-field (10 G) and high-field (up to 5000 G) magnetization data, are consistent with ferromagnetic interactions on the scale of the crystal lattice with two critical temperatures: 6.4 and 4.4 K. The former critical temperature could correspond to a transition from a paramagnetic to a ferromagnetic state; the latter one, to a transition from a ferromagnetically ordered state to its 3D ordering. The magnetic data, along with the field dependence of the magnetization and the EPR data, are also in line with a soft magnet. Moreover, the EPR studies performed on 4 reveal unique features reported for the first time in the field of molecular magnetism.