Cadmium(ii) and mercury(ii) complexes of an NO2S2-donor macrocycle and its ditopic xylyl-bridged analogue

Abstract

The NO₂S₂-donor macrocycle (L¹) was synthesised from the ring closure reaction between Boc-N-protected 2,2′-iminobis(ethanethiol) (3) and 2,2′-(ethylenedioxy)bis(benzyl chloride) (4) followed by deprotection of the Boc-group. α,α′-Dibromo-p-xylene was employed as a dialkylating agent to bridge two L¹ to yield the corresponding N-linked product (L²). The X-ray structure of L² (as its HBr salt) is described. A range of Cd(II) and Hg(II) complexes of L¹ (6–9) and L² (10–12) were prepared and characterised. Reaction of HgX₂ (X = Br or I) with L¹ afforded [Hg(L¹)Br]₂[Hg₂Br₆]·2CH₂Cl₂6 and [Hg(L¹)I₂] 7, respectively. For 6, the Hg(II) ion in the complex cation has a distorted tetrahedral coordination environment composed of S₂N donor atoms from L¹ and a bromo ligand. In 7 the coordination geometry is highly distorted tetrahedral, with the macrocycle coordinating in an exodentate manner via one S and one N atom. The remaining two coordination sites are occupied by iodide ions. [Hg(L¹)(ClO₄)]ClO₄8 was isolated from the reaction of Hg(ClO₄)₂ and L¹. The X-ray structure reveals that all macrocyclic ring donors bind to the central mercury ion in this case, with the latter exhibiting a highly distorted octahedral coordination geometry. The O₂S₂-donors from the macrocyclic ring define the equatorial plane while the axial positions are occupied by the ring nitrogen as well as by an oxygen from a monodentate perchlorato ion. Reaction of Cd(NO₃)₂·4H₂O with L¹ afforded [Cd(L¹)(NO₃)₂]·0.5CH₂Cl₂9 in which L¹ acts as a tridentate ligand, binding exo-fashion via its S₂N donors. The remaining coordination positions are filled by two bidentate nitrate ions such that, overall, the cadmium is seven-coordinate. Reactions of HgX₂ (X = Br or I) with L² yielded the isostructural 2 : 1 (metal : ligand) complexes, [Hg₂(L²)Br₄] 10 and [Hg₂(L²)I₄] 11. Each mercury ion has a distorted tetrahedral environment made up of S and N donors from an exodentate L² and two coordinated halides. Contrasting with this, the reaction of L² with Cd(NO₃)₂·4H₂O yielded a 1-D coordination network, {[Cd₂(L²)(NO₃)₄]·2CH₂Cl₂}_n12 in which each ring of L² is exo-coordinated via two S atoms and one N atom to a cadmium ion which is also bound to one monodentate and one bidentate nitrate anion. The latter also has one of its oxygen atom attached to a neighboring cadmium via a nitroso (µ₂-O) bridge such that the overall coordination geometry about each cadmium is seven-coordinate. The [Cd(L²)_0.5(NO₃)₂] units are linked by an inversion to yield the polymeric arrangement.