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 [Cu2(L1)(OAc)2], [Cu2(L2)(H2O)2(OAc)3] and [CuII2(L1)(NCS)2]; in the last of these one equivalent of NaNCS per copper(II) ion was also added. The fourth complex, [Cu2(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 [Cu2(L1)(OAc)2]·2MeOH·H2O and [Cu2(L2)(H2O)2(OAc)3] is unidentate as had been tentatively predicted by analysis of the infrared spectra (ΔOCO 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 [Cu2(L1)(OAc)2]·2H2O and [CuII2(L1)(NCS)2]·DMF respectively. The J values have been discussed in relation to a published correlation involving the CuNpyrazolateNpyrazolate angles.