Conformational and stereochemical flexibility in cadmium(II) complexes of aza-thioether macrocycles.

The synthesis and crystal structures of four CdII macrocyclic complexes containing mixed N-, O- and S-donors, [Cd(NO3)2([12]aneN2S2)] (1), [Cd(NO3)2([12]aneNS3)] (2), [Cd(NO3)2([15]aneNO2S2)] (3) and [Cd(NO3)([15]aneN2O2S)]NO3 (4), are presented. The metal ion is coordinated outside of the macrocyclic cavity in the complexes of the smaller macrocycles ([12]aneN2S2 and [12]aneNS3) while the flexibility of the larger macrocycles in and allows very different conformations to be adopted with a 'butterfly' geometry in and a flattened geometry in. No correlation between the number of sulfur donors and Cd-S bond distance in these types of complexes is observed, although the number and binding mode of the nitrato ligands is determined by the conformation and binding mode of the macrocycle. The position of the nitrato ligand also influences, through steric conflicts with the macrocyclic donor atoms, the bond distances in both ligand systems.