Synthesis and structures of dinuclear cryptates with Zn(ii), Cd(ii) and Hg(ii): tuning the cascade binding mode with metal ions

Abstract

The crystal structures of eight cascade complexes, [Zn₂L(μ-Cl)](ClO₄)₃·2H₂O·3CH₃CN (1), [Zn₂L(μ-Br)](ClO₄)₃·2H₂O·3CH₃CN (2), [Cd₂L(μ-OH)]₂[CdI₄]₃·6DMF (3), [Cd₂L(μ-Cl)][CdCl₄](Cl)·4.5H₂O (5), [Cd₂L(μ-Br)][CdBr₄](Br)·1.5H₂O (6), [Hg₂L(μ-Cl)][HgCl₄](Cl)·6H₂O (9), [Hg₂L(μ-Br)][HgBr₄](Br)·1.25H₂O (10), and [Hg₂L(μ-I)](NO₃)₃·6H₂O (11), were presented, which reveal the influence of the coordinated metal ions on the selectivity in the cascade binding mode. The dizinc(II) cryptate shows the recognition of Cl⁻ and Br⁻ rather than that of F⁻ and I⁻. Unexpectedly, the dicadmium(II) cryptate shows the recognition of OH⁻, F⁻, Cl⁻ and Br⁻ rather than that of I⁻, while all of the above-mentioned anions can form stable cascade complexes with the dimercury(II) cryptate. For better understanding, the binding behaviors and stabilisation energies between [M₂L]⁴⁺ and anions were calculated by DFT calculations.