Synthesis and electrochemistry of nickel and cobalt complexes of mixed thia–aza crown ethers: single-crystal structures of [Ni([18]aneN2S4)][PF6]2·0.33H2O and [CO([18]aneN2S4)][PF6]3·3H2O ([18]aneN2S4= 1,4,10,13-tetrathia-7,16-diazacyclooctadecane)

Abstract

The mixed thia–aza donor macrocyclic complexes [M([18]aneN₂S₄)]²⁺(M = Ni or Co; [18]aneN₂S₄= 1,4,10,13-tetrathia-7,1 6-diazacyclooctadecane) and [Ni(Me₂[18]aneN₂S₄)]²⁺(Me₂[18]aneN₂S₄= 7,16-dimethyl-1,4,10,13-tetrathia-7,16-diazacyclooctadecane) were prepared by reaction of M(NO₃)₂·6H₂O with the appropriate crown ether in aqueous ethanol. The complex [Ni([18]aneN₄S₄)][PF₆]₂·0.33H₂O crystallises in the orthorhombic space group Pcab with a= 12.8260(20), b= 18.083(3), c= 22.200(4)Å and Z= 8. The structure shows the Ni^II encapsulated in a near-octahedral geometry, with the macrocycle adopting a rac configuration. Both diastereoisomeric forms of rac-[Ni([18]aneN₂S₄)]²⁺ are present in the crystal structure in approximately 1 : 1 ratio. Aerial oxidation of [Co([18]aneN₂S₄)][PF₆]₂ in water afforded the corresponding cobalt (III) complex: [Co([18]aneN₂S₄)][PF₆]₃·3H₂O crystallises in the monoclinic space group P2₁/n with a= 11.5485(3), b= 13.9779(2), c= 19.1378(4)Å, β= 106.561 (2)° and Z= 4. The structure shows the Co^III bound to all six macrocyclic donors in a distorted-octahedral geometry. The ligand adopts a rac configuration around the metal centre. In both complexes there is a small but significant tetrahedral distortion of the four sulfur donors out of the best S₄ co-ordination plane. The complex [Co([18]aneN₂S₄)][PF₆]₃·3H₂O exhibits an extensive hydrogen-bonding network involving the macrocyclic cation, PF₆^– anions and H₂O solvent molecules. Electrochemical data, electronic and ESR spectroscopic data for the complexes are also discussed in the context of their donor sets and ligand configurations and conformations.