2-Pyridylselenyl halides undergo facile coupling with a triple CN bond of unactivated nitriles. Unprecedented heterocyclization allowed the preparation of novel class of cationic 1,2,4-selenadiazoles in remarkably high yields. Cationic 1,2,4-selenadiazoles...

Supramolecular chemistry of chalcogenadiazoles is attracting an increasing attention due to its applications in materials chemistry. Chalcogen bonding allows a fine-tuning of the self-assembly and, therefore, modulation of physical properties when these compounds are employed. Here, we report a facile preparation of a broad scope of 1,2,4-selenadiazoles via coupling of 2-pyridylselenenyl halides with unactivated nitriles, that represent a novel type of supramolecular building blocks which eagerly engage in a variety of chalcogen bonding interactions. The substituent-dependent propensity of novel selenadiazoles for the formation of four-center Se···N chalcogen bonding is analyzed. Other weak interactions, which in some cases outcompete the formation of 2Se–2N squares, are described. The discovery of the adducts derived from α-halogenated nitriles, which form robust dimers featuring a very specific combination of 2Se–2N square, two Hal···Hal, and two Se···Hal noncovalent interactions, is presented.

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The synthesis of 2-pyridyltellurenyl bromide via Br2 oxidative cleavage of the Te–Te bond of dipyridylditelluride is reported. Single-crystal X-ray diffraction analysis of 2-pyridyltellurenyl bromide demonstrated that the Te atom of 2-pyridyltellurenyl bromide was involved in four different noncovalent contacts: Te⋯Te interactions, two Te⋯Br ChB, and one Te⋯N ChB contact forming 3D supramolecular symmetrical framework. In contrast to 2-pyridylselenenyl halides, the Te congener does not react with nitriles furnishing cyclization products. 2-Pyridylselenenyl chloride was demonstrated to easily form the corresponding adduct with benzonitrile. The cyclization product was studied by the single-crystal X-ray diffraction analysis, which revealed that in contrast to earlier studied cationic 1,2,4-selenadiazoles, here we observed that the adduct with benzonitrile formed supramolecular dimers via Se⋯Se interactions in the solid state, which were never observed before for 1,2,4-selenadiazoles.

Keywords: Tellurium / Multinuclear NMR spectroscopy / IR spectroscopy / Raman spectroscopy / X-ray diffraction / Quantum chemistry Two new stable T-shaped tellurenyl chloride adducts, viz., [HPy*]TeCl 2 (1) and [HPm*]TeCl 2 (2) [Py* = 2-pyridyl, Pm* = 2-(4,6-dimethyl)pyrimidyl], act as close chemical analogs of highly unstable monomeric Py*TeCl and Pm*TeCl. The quasi-planar zwitterionic structures of 1 and 2 have been studied by experimental (X-ray diffraction, multinuclear[a] A. N. 3582NMR, IR and Raman spectroscopy) and theoretical (DFT and QTAIM) methods. Thus, a novel facile route to stabilize highly reactive Ar*TeCl species (Ar* = N-functionalized aryl) by the addition of a hydrochloric acid molecule has been demonstrated.Scheme 1. Reaction of di(2-pyridyl) ditelluride or bis(4,6-dimethyl-2-pyrimidyl) ditelluride with sulfuryl chloride.

1H-Pyridine-2-selenenyl dibromide, C5H5NSeBr2, 1, is a product of the bromination of bis(pyridin-2-yl) diselenide in methylene chloride recrystallization from methanol. Compound 1 is essentially zwitterionic: the negative charge resides on the SeBr2 moiety and the positive charge is delocalized over the pyridinium fragment. The C—Se distance of 1.927 (3) Å is typical of a single bond. The virtually linear Br—Se—Br moiety of 178.428 (15)° has symmetrical geometry, with Se—Br bonds of 2.5761 (4) and 2.5920 (4) Å, and is twisted by 63.79 (8)° relative to the pyridinium plane. The Se atom forms an intermolecular Se...Br contact of 3.4326 (4) Å, adopting a distorted square-planar coordination. In the crystal, molecules of 1 are linked by intermolecular N—H...Br and C—H...Br hydrogen bonds, as well as by non-covalent Se...Br interactions, into a three-dimensional framework. (3aSR,(9aRS)-2,3,3a,9a-Tetrahydro-1H-cyclopenta[4,5][1,3]selenazolo[3,2-a]pyridinium-9 bromide, C10H12NSe+·Br−, 2, is a product of the cycloaddition reaction of 1 with cyclopentene. Compound 2 is a salt containing a selenazolopyridinium cation and a bromide anion. Both five-membered rings of the cation adopt envelope conformations. The dihedral angle between the basal planes of these rings is 62.45 (11)°. The Se atom of the cation forms two additional non-covalent interactions with the bromide anions at distances of 3.2715 (4) and 3.5683 (3) Å, attaining a distorted square-planar coordination. In the crystal, the cations and anions of 2 form centrosymmetric dimers by non-covalent Se...Br interactions. The dimers are linked by weak C—H...Br hydrogen bonds into double layers parallel to (001).

New unsymmetrical monoterpenylhetaryl disulfides based on heterocyclic disulfides and monoterpene thiols were synthesized for the first time in 48–88% yields. Hydrolysis of disulfides with fragments of methyl esters of 2-mercaptonicotinic acid was carried out in 73–95% yields. The obtained compounds were evaluated for antioxidant, antibacterial, antifungal activity, cytotoxicity and mutagenicity.

The title compound, C10H12Cl3NTe, crystallizes with two crystallographically independent mol­ecules (A and B) in the asymmetric unit. In each case, the coordination around the Te atom is distorted square-pyramidal, with the equatorial plane composed of the three Cl atoms and the C atom of the pyridinium ring. The Te atom is displaced from the mean-square plane by 0.1926 (7) and 0.1981 (8) Å, in mol­ecules A and B, respectivly, away from the apical C atom. The bond lengths from the Te atom to the two Cl atoms arranged trans to each other [2.5009 (7)/2.5145 (7) and 2.5184 (7)/2.5220 (8) Å in mol­ecules A and B, respectivly] are substan­ti­ally shorter than the third Te—Cl distance [2.8786 (7) and 2.8763 (7) Å in mol­ecules A and B, respectivly]. The 1,3-tellurazole ring is almost planar (r.m.s. deviations of 0.042 and 0.045 Å in mol­ecules A and B, respectivly). The cyclopentane rings in both molecules A and B adopt envelope conformations with the carbon atom opposed to the (Te)C—C(N) bond as the flap. In the crystal, mol­ecules form centrosymmetric 2 + 2 associates via Te⋯Cl inter­actions [3.3993 (7) and 3.2030 (7) Å]. As a result of these secondary inter­actions, the Te atom attains a strongly distorted 5 + 1 octa­hedral environment. Further, the 2 + 2 associates are bound by weak C—H⋯Cl hydrogen bonds into a three–dimensional framework.