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)A and Z= 8. The structure shows the NiII 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)A, β= 106.561 (2)° and Z= 4. The structure shows the CoIII 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.