Building new discrete supramolecular assemblies through the interaction of iso-tellurazole N-oxides with Lewis acids and bases

An Unusual Macrocyclic Hexamer of an Iso-Tellurazole N-Oxide Featuring CTe… O Chalcogen Bonds is Formed by κ6 -O Complexation to Fe(II) and Ni(II)

Studies of the supramolecular chemistry of iso-tellurazole N-oxides have been confined to non-polar media until now. To overcome that limitation, an iso-tellurazole N-oxide was derivatized with a primary alcohol group; the compound is soluble in polar solvents and stable in acidic to neutral aqueous media. Nickel (II) and iron (II) form macrocyclic complexes with six molecules of that iso-tellurazole N-oxide in a hitherto not-observed macrocyclic arrangement defined by CTe⋅⋅⋅O chalcogen bonds and κ6 -O bound to the metal ion. This behaviour is in sharp contrast with the κn -Te (n=1,2,4) complexes formed by soft metal ions.

Organotelluroxane molecular clusters assembled via Te⋯X- (X = Cl-, Br-) chalcogen bonding anion template interactions

The synthesis and characterisation of two novel molecular organotelluroxane clusters, comprising of an inorganic Te₈O₆X₄ (X = Cl, Br) core structure are described. The integration of highly electron withdrawing 3,5-bis-trifluoromethylphenyl groups to the constituent Te(IV) centres is determined to be crucial in the chalcogen bonding (ChB) halide template directed assembly. Characterised by multi-nuclear ¹H, ¹²⁵Te, ¹⁹F NMR, UV-Vis, IR spectroscopies and X-ray crystal structure analysis, the discrete molecular clusters exhibit excellent organic solvent solubility and remarkable chemical stability. Furthermore, preliminary fluorescence investigations reveal the telluroxanes exhibit aggregation induced emission (AIE) behaviour in organic aqueous solvent mixtures.

Unexpected ring closures leading to 2-N,N-dialkylaminoareno[1,3]tellurazoles

One step, up to 78% isolated yield, six examples. Facile access to 2-N,N-dialkylbenzo[1,3]tellurazoles.

Iso-Tellurazolium-N-Phenoxides: A Family of Te···O Chalcogen-Bonding Supramolecular Building Blocks

Formal substitution of the oxygen atom of an iso-tellurazole N-oxide with deprotonated (ortho, meta, and para)-hydroxyphenyl groups generated molecules that readily aggregate through Te···O chalcogen bonding (ChB) interactions. The molecules undergo autoassociation in solution, as shown by variable temperature (VT) ¹H NMR experiments and paralleling the behavior of iso-tellurazole N-oxides. Judicious adjustment of crystallization conditions enabled the isolation of either polymeric or macrocyclic aggregates. Among the latter, the ortho compound assembled a calixarene-like trimer, while the para isomer built a macrocyclic tetramer akin to a molecular square. The Te···O ChB distances in these structures range from 2.13 to 2.17 Å, comparable to those in the structures of iso-tellurazole N-oxides. DFT calculations estimate that the corresponding Te···O ChB energies are between -122 and -195 kJ mol^-1 in model dimers and suggest that macrocyclic aggregation enhances these interactions.

Competing Effects of Chlorination on the Strength of Te⋅⋅⋅O Chalcogen Bonds Select the Structure of Mixed Supramolecular Macrocyclic Aggregates of Iso-Tellurazole N-Oxides

Chlorination of 3-methyl-5-phenyl-1,2-tellurazole-2-oxide yielded the λ⁴ Te dichloro derivative. Its crystal structure demonstrates that the heterocycle retains its ability to autoassociate by chalcogen bonding (ChB) forming macrocyclic tetramers. The corresponding Te⋅⋅⋅O ChB distances are 2.062 Å, the shortest observed to date in aggregates of this type. DFT-D3 calculations indicate that while the halogenated molecule is stronger as a ChB donor it also is a weaker ChB acceptor; the overall effect is that the ChBs in the chlorinated homotetramer are not significantly stronger. However, partial halogenation or scrambling selectively yield the 2 : 2 heterotetramer with alternating λ⁴ Te and λ² Te centers, which calculations identified as the thermodynamically preferred arrangement.

Synthetic and structural investigations of bis(N-alkyl-benzoselenadiazolium) cations

A variety of supramolecular structures is formed by selenadiazolium cations linked by hydrocarbon bridges.

Macrocyclic complexes of Pt(ii) and Rh(iii) with iso-tellurazole N-oxides

Tetramers of iso-tellurazole N-oxides form stable macrocyclic complexes with Pt(ii) and Rh(iii) in solution.

Sigma-hole interactions in the molecular and crystal structures of N-boryl benzo-2,1,3-selenadiazoles

Crystallography and DFT reveal competition between chalcogen bonding and other intermolecular interactions.