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Abstract
Despite their versatility, the application of telluradiazoles as supramolecular building blocks is considerably constrained by their sensitivity to moisture. Albeit more robust, their selenium analogues form weaker supramolecular interactions. These, however, are enhanced when one nitrogen atom is bonded to an alkyl group. Here we investigate general methods for the synthesis of such derivatives. Methyl, iso-propyl and tert-butyl benzo-2,1,3-selenadiazolium cations were prepared by direct alkylation or cyclo-condensation of the alkyl-phenylenediamine with selenous acid. While the former reaction only proceeds with the primary and tertiary alkyl iodides, the latter is very efficient. Difficulties reported in earlier literature are attributable to the formation of adducts of benzoselenadiazole with its alkylated cations and side reactions initiated by aerobic oxidation of iodide. However, the cations themselves are resilient to oxidation and stable in acidic to neutral aqueous medium. X-ray crystallography was used in the identification and characterization of the following compounds: [C6H4N2(R)Se](+)X(-), (R = CH(CH3)2, C(CH3)3; X = I(-), I3(-)], [C6H4N2(CH3)Se](+)I(-), and [C6H4N2Se][C6H4N2(CH3)Se]2I2. Formation of SeN secondary bonding interactions (chalcogen bonds) was only observed in the last structure as anion binding to selenium is a strong competitor. The relative strengths of those forces and the structural preferences they enforce were assessed with DFT-D3 calculations supplemented by AIM analysis of the electron density.
Highlights
While hydrogen bonding and the coordination of metal ions are preponderant in supramolecular chemistry, other interactions are receiving increasing interest in this field
Their molecules usually associate by two antiparallel Te⋯N secondary bonding interactions forming the [Te–N]2 supramolecular synthon,[5] a virtual four-membered ring (Scheme 1, E = Te).[6]
The Adiabatic Local Density Approximation (ALDA) was used for the exchange–correlation kernel[30,31] and the differentiated static LDA expression was used with the Vosko–Wilk–Nusair parameterization.[32,33]
Summary
While hydrogen bonding and the coordination of metal ions are preponderant in supramolecular chemistry, other interactions are receiving increasing interest in this field. The potential of secondary bonding in supramolecular chemistry is well exemplified by the derivatives of the 1,2,5-telluradiazole ring (1, Chart 1). Their molecules usually associate by two antiparallel Te⋯N secondary bonding interactions forming the [Te–N]2 supramolecular synthon,[5] a virtual four-membered ring (Scheme 1, E = Te).[6] In the absence of substantial steric hindrance, each molecule can simultaneously form the Chart 1 Scheme 1 This effect induces properties such as chromotropism[8] and second-
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