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

Abstract

Chlorination of 3-methyl-5-phenyl-1,2-tellurazole-2-oxide yielded the λ 4 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. DFTÀ 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 λ 4 Te and λ 2 Te centers, which calculations identified as the thermodynamically preferred arrangement.Chalcogen bonding (ChB), [1][2][3][4][5][6][7] i. e. the attractive supramolecular interaction of electrophilic sites on atoms of heavy group 16elements (S, Se, Te) with electron-rich centers, has unveiled an array of fascinating chemistry in fields as diverse as Lewis-acid catalysis, [8][9][10][11][12][13][14][15] optical probes, [14,16,17] functional materials, [5,[18][19][20][21][22][23][24] crystal engineering, [25][26][27][28][29][30] ion recognition and transport, [22,[31][32][33][34][35][36] and protein folding. [37] Amongst the many molecules capable of forming ChBs, isotellurazole N-oxides (1, Scheme 1) stand apart because of their ability to spontaneously assemble cyclic tetramers (1 4 ) and hexamers (1 6 ) that exist in equilibrium in solution. [38][39][40] There are two electrophilic regions on the tellurium atom of 1, antipodal to each the NÀ Te and the CÀ Te bonds. The former has a larger V max and, consequently, the Te•••O ChB interaction in all known cases is formed trans to the N atom (e. g. 1 4,6 in Scheme 1). The Te•••O ChBs are reversible, scrambling is[a] P.

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

“…The balance of competing effects selectively assembles 2:2 heterotetramers with alternating Te(II) and Te(IV) centers when 1b is partially chlorinated or combined with an equimolar amount of 1bCl 2 . 38 Despite the reversible nature of ChBs, the annular aggregates of 1 and 2 behave as veritable macrocycles capable of coordinating transition metal ions, 33,39,40 forming adducts with C 60 and hosting small molecules. 33 Nevertheless, the cavities of 1 4 and 1 6 are small, transannular Te−Te distances range from 5.5 Å in 2a 4 to 7.6 Å in 1b 6 .…”

“…Molecules of 1 Cl 2 are stronger ChB donors but weaker ChB acceptors than 1 . The balance of competing effects selectively assembles 2:2 heterotetramers with alternating Te­(II) and Te­(IV) centers when 1b is partially chlorinated or combined with an equimolar amount of 1b Cl 2 …”

Predictability of Chalcogen-Bond-Driven Crystal Engineering: An X-ray Diffraction and Selenium-77 Solid-State NMR Investigation of Benzylic Selenocyanate Cocrystals

“…Such deviations, along with the existence of two σ-holes, render the predictability of ChB interactions more challenging, and the uses of these interactions based on the tenets of crystal engineering are somewhat limited. A number of crystal structures of amphoteric chalcogen-bonded molecules are known, wherein a molecule behaves as both the ChB donor and acceptor, such as dicyanoselenide, dicyanotelluride, benzoselenadiazoles, selenophthalic anhydrides, telluradiazoles, and iso-tellurazole N -oxides . There are also several instances of heteromeric systems designed purely based on chalcogen bonds; for example, dicyanotelluradiazole and dicyanoselenadiazole cocrystallized with anions; benzotelluradiazole derivatives and thiophenes as anionic receptors; , thiophene, selenophene, and tellurophene receptors for anion recognition; intermolecular ChB with chalcogenadiazoles and in pure iso-tellurazole N -oxides; , chalcogenazolo-pyridine scaffolds; and considerable work from Fourmigué and co-workers on organic selenocyanate derivatives as strong, directional chalcogen bond donors with utility in crystal engineering applications. ,− …”

“…A number of crystal structures of amphoteric chalcogen-bonded molecules are known, wherein a molecule behaves as both the ChB donor and acceptor, such as dicyanoselenide, 34 dicyanotelluride, 35 benzoselenadiazoles, 18 selenophthalic anhydrides, 32 telluradiazoles, 36 and iso-tellurazole N -oxides. 37 There are also several instances of heteromeric systems designed purely based on chalcogen bonds; for example, dicyanotelluradiazole and dicyanoselenadiazole cocrystallized with anions; 38 benzotelluradiazole derivatives and thiophenes as anionic receptors; 39 , 40 thiophene, selenophene, and tellurophene receptors for anion recognition; 41 intermolecular ChB with chalcogenadiazoles and in pure iso-tellurazole N -oxides; 18 , 42 chalcogenazolo-pyridine scaffolds; 43 and considerable work from Fourmigué and co-workers on organic selenocyanate derivatives as strong, directional chalcogen bond donors with utility in crystal engineering applications. 23 , 44 − 47 …”

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

“…14,15 Similarly, self-assembly was documented for structurally related compounds. [16][17][18] However, TeÁ Á ÁN interactions were only found in 11% of crystals where they can potentially form. 12 Little remains known about the tendency of six-membered Te, N heterocycles to form supramolecular aggregates.…”