Metal Complexes with Macrocyclic Ligands. Part XLVI. Synthesis and structures of dinuclear metal complexes of bis‐macrocycles having a pyrazole bridging unit

Abstract

AbstractThree bis‐macrocyclic ligands consisting of two N3‐, 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 CuII and NiII complexes which are able to bind one additional exogenous bridging molecule such as Cl−, Br−, N, SO, 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 Å. In the dinuclear Cu2+ complexes, antiferromagnetic coupling is present. The azido‐bridged complex shows a very strong interaction with −2J ≥ 1040 cm−1; in contrast, the H‐pyrazol‐1‐ide and chloride bridged species have −2J values of 300 and 272cm−1, respectively. Cyclic voltammetry of the Cu2+ complexes in MeCN reveals a strong dependence of the potentials CuII/Cu‐II → CuII/CuI → CuI/CuI 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 Cu1 oxidation state.