s-Block Complexes of iso-Tellurazole N-Oxides

Abstract

The study of the macrocyclic aggregates of iso-tellurazole N-oxide has previously unveiled a wide variety of complexes with transition metal ions. The compound 3-methyl-5-phenyl-1,2-tellurazole-2-oxide and its derivatives bind soft d6, d8 and d10 metal ions exclusively by tellurium. The electron withdrawing ability of the cations strengthen the Te…O chalcogen bonding (ChB) interactions. In this thesis, we investigated the coordination chemistry of iso-tellurazole N-oxide with hard metal ions from elements of groups 1 and 2, as salts with weakly-coordinating anions. X-ray crystallography of the isolated products showed that the oxophilic nature of these cations results in coordination to the oxygen atom. However, formation of Te…O ChBs is not inhibited, in contrast to the cases in which oxygen binds protons or boranes. Novel dodecameric macrocycles were obtained from experiments with Na+ cations. The large supramolecular ring folds onto itself forming a cage-like structure capable of hosting molecules such as dioxane, THF and pyrazine. Their encapsulation is facilitated by the coordination to the metal ion. In the absence of such molecular guests, a tris-tetramer structure was assembled with four sodium ions. Although full refinement of its crystal structure is yet to be completed, the tris-tetramer suggests a mechanism that leads to the formation of the dodecamers. In contrast to Na+, K+ yielded a 1-D coordination polymer of the tetramers. The more oxophilic Mg2+ yielded complexes of macrocyclic hexamers of iso-tellurazole oxides linked by C-Te…O ChBs.