Metal complexes with macrocyclic ligands - Part XLVI - Synthesis and structures of dinuclear metal complexes of bis-macrocycles having a pyrazole bridging unit

Three bis-macrocyclic ligands consisting of two N-3-, N2S-, or NS2-cyclononane rings, i.e., of two octahydro-1H-1,4,7-triazonine, octahydro-1,4,7-thiadiazonine, or hexahydro-5H-1,4-7-dithiazonine rings, connected by a 1H-pyrazolediyl unit were prepared. They form dinuclear Cu-II and Ni-II complexes which are able to bind one additional exogenous bridging molecule such as Cl-, Br-, N-3(-), SO42-, and 1H-pyrazol-1-ide. The structures determined by X-ray diffraction show that each Cu2+ is coordinated by the three donor atoms of the macrocyclic ring, by a pyrazolidodiyl N-atom, by an atom of the exogenous bridging ligand, and sometimes by a solvent molecule. In the majority of the Cu2+ cases, the metal ion exhibits square-pyramidal or trigonal-bipyramidal coordination geometry, except in the sulfato-bridged complex, in which one Cu2+ is hexacoordinated with the participation of a water molecule. The X-ray structure of the azide-bridged dinuclear Ni2+ complex was also solved and shows that both Ni2+ centres have octahedral coordination geometries. In all complexes, the 1H-pyrazolediyl group connecting the macrocycles is deprotonated and bridges the two metal centres, which, depending on the exogenous ligand, have distances between 3.6 and 4.5 Angstrom. In the dinuclear Cu2+ complexes, antiferromagnetic coupling is present. The azido-bridged complex shows a very strong interaction with -2J greater than or equal to 1040 cm(-1); in contrast, the 1H-pyrazol-1-ide and chloride bridged species have -2J values of 300 and 272 cm(-1), respectively. Cyclic voltammetry of the Cu2+ complexes in MeCN reveals a strong dependence of the potentials Cu-II/ Cu-II --> Cu-II/Cu-I --> Cu-I/Cu-I on the nature of the donor atoms of the macrocycle as well as on the type of bridging molecule. The more S-donors are present in the macrocycle, the higher is the potential, indicating a stabilization of the Cu-I oxidation state.