Premium
Metal Complexes with Macrocyclic Ligands. Part XLVI . Synthesis and structures of dinuclear metal complexes of bis‐macrocycles having a pyrazole bridging unit
Author(s) -
Weller Harald,
Siegfried Liselotte,
Neuburger Markus,
Zehnder Margareta,
Kaden Thomas A.
Publication year - 1997
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19970800804
Subject(s) - chemistry , crystallography , metal , deprotonation , ligand (biochemistry) , molecule , trigonal bipyramidal molecular geometry , pyrazole , stereochemistry , square pyramidal molecular geometry , octahedron , bridging ligand , crystal structure , ion , biochemistry , receptor , organic chemistry
Three bis‐macrocyclic ligands consisting of two N 3 ‐, N 2 S‐, or NS 2 ‐cyclononane rings, i.e., of two octahydro‐1 H ‐1,4,7‐triazonine, octahydro‐1,4,7‐thiadiazonine, or hexahydro‐5 H ‐1,4‐7‐dithiazonine rings, connected by a 1 H ‐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 − , SO 4 2− , and 1 H ‐pyrazol‐1‐ide. The structures determined by X‐ray diffraction show that each Cu 2+ 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 Cu 2+ cases, the metal ion exhibits square‐pyramidal or trigonal‐bipyramidal coordination geometry, except in the sulfato‐bridged complex, in which one Cu 2+ is hexacoordinated with the participation of a water molecule. The X‐ray structure of the azide‐bridged dinuclear Ni 2+ complex was also solved and shows that both Ni 2+ centres have octahedral coordination geometries. In all complexes, the 1 H ‐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 Cu 2+ complexes, antiferromagnetic coupling is present. The azido‐bridged complex shows a very strong interaction with −2 J ≥ 1040 cm −1 ; in contrast, the H ‐pyrazol‐1‐ide and chloride bridged species have −2 J values of 300 and 272cm −1 , respectively. Cyclic voltammetry of the Cu 2+ 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 1 oxidation state.