Synthesis, structures and magnetic properties of three copper(II) complexes of 2-(1H-pyrazol-3-yl) pyridine

Three Cu(II) complexes: [Cu-2(mu-L)(2)(HCOO)(2)(H2O)(2)] (1), [Cu-2(mu-L)(2)(NO3)(2)] (2), and [Cu-4(mu-L)(6)(CH3COO)(2)]center dot 2H(2)O (3) constructed from 2-(1H-pyrazol-3-yl) pyridine (HL) were synthesized and structurally characterized by X-ray single-crystal diffraction. The X-ray analyses revealed that all three complexes feature a di-ligand-bridged Cu-2 unit, which is nearly planar. Each deprotonated ligand chelates one copper atom by means of N,N(pyridine-pyrazole) pocket and simultaneously bridges the other one by the N,N(pyrazole) groups. The remaining coordination sites of the Cu(II) centers are either occupied by different anionic coligands to balance the charge, or bridged by another L to develop a tetranuclear structure. Magnetic investigations reveal that the distortion of the Cu(II) coordination geometry (as described by the tau values) and the coplanarity of the Cu-(N=N)(2)-Cu unit have cooperative effects on the antiferromagnetic strength of these systems.