Dicopper(II) complexes of a new pyrazolate-containing Schiff-base macrocycle and related acyclic ligand

Dicopper(II) complexes of two new 3,5-disubstituted-pyrazole-based ligands, bis(quadridentate) macrocyclic ligand (L1)(2-) and bis(terdentate) acyclic ligand (L2)(-), were synthesised by Schiff base condensation of 3,5-diformylpyrazole and either one equivalent of 1,3-diaminopropane or two equivalents of 2-( 2- aminoethyl) pyridine in the presence of one or two equivalents of copper( II) ions, respectively. Copper( II) acetate monohydrate was employed in the synthesis of [Cu-2(L1)(OAc)(2)], [Cu-2(L2)(H2O)(2)(OAc)(3)] and [Cu-2(II)(L1)(NCS)(2)]; in the last of these one equivalent of NaNCS per copper(II) ion was also added. The fourth complex, [Cu-2(L2)(NCS)(2)(DMF)]BF4, was prepared using copper( II) tetrafluoroborate hexahydrate, along with two equivalents of NaOH and six of NaSCN. All four of these dimetallic complexes have been characterised by single crystal X-ray diffraction: the two macrocyclic complexes are the first such Schiff base complexes to be so characterised. A feature common to all four of the structures is bridging of the two copper( II) centres by the pyrazolate moiety/moieties. The structure determinations show that the coordination mode of the acetate groups in both [Cu-2(L1)(OAc)(2)]center dot 2MeOH center dot H2O and [Cu-2(L2)(H2O)(2)(OAc)(3)] is unidentate as had been tentatively predicted by analysis of the infrared spectra (Delta OCO of 199 and 208 cm(-1), respectively). The magnetochemical studies of the macrocyclic complexes, over the temperature range 4 - 300 K, revealed strong antiferromagnetic coupling with J = -169 and -213 cm(-1) for [Cu-2(L1)(OAc)(2)]center dot 2H(2)O and [Cu-2(II)(L1)(NCS)(2)]center dot DMF respectively. The J values have been discussed in relation to a published correlation involving the CuNpyrazolateNpyrazolate angles.