Hg(II) and Cd(II) complexes with mixed donor macrocyclic thioethers: The oxophobicity of mercury(II)

A series of Hg(II) and Cd(II) homoleptic complexes with mixed donor (O,S and N,S) macrocycles is reported. The macrocyclic oxa thiacrowns 9S2O (1-oxa-4,7-dithiacyclononane) and 18S4O2 (1,10-dioxa-4,7,13,16-tetrathiacyclooctadecane) bind to Hg(II) to form distorted tetrahedral S4 geometries without coordination of the oxygen atoms. In contrast, the two macrocycles coordinate to Cd(II) through all ligand donors to form S4O2 environments. We also report the structure of bis(9N2S (1,4-diaza-7-thiacyclononane))cadmium(II), Cd(9N2S)₂]²⁺ which shows octahedral coordination in a trans N4S2 environment. Furthermore, two new homoleptic Cd(II) complexes with the related hexadentate macrocycles 18N6 (1,4,7,10,13,16-hexaazacyclooctadecane) and 18S6 (1,4,7,10,13,16-hexathiayclooctadecane) are described. Among the Cd(II) complexes, we highlight a trend in ¹¹³Cd NMR that shows progressive upfield chemical shifts as secondary amine donors replace thioether S donors.