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