Abstract
1H-Pyridine-2-selenenyl dibromide, C5H5NSeBr2, 1, is a product of the bromination of bis-(pyridin-2-yl) diselenide in methyl-ene 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 inter-molecular Se⋯Br contact of 3.4326 (4) Å, adopting a distorted square-planar coordination. In the crystal, mol-ecules of 1 are linked by inter-molecular N-H⋯Br and C-H⋯Br hydrogen bonds, as well as by non-covalent Se⋯Br inter-actions, into a three-dimensional framework. (3aSR,(9aRS)-2,3,3a,9a-Tetra-hydro-1H-cyclo-penta[4,5][1,3]selenazolo[3,2-a]pyridinium-9 bromide, C10H12NSe+·Br-, 2, is a product of the cyclo-addition reaction of 1 with cyclo-pentene. 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 inter-actions 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 inter-actions. The dimers are linked by weak C-H⋯Br hydrogen bonds into double layers parallel to (001).
Highlights
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 dimers are linked by weak C— HÁ Á ÁBr hydrogen bonds into double layers parallel to (001)
Summary
Selenium-containing molecules have attracted significant attention from chemical and medicinal scientists because of their wide range of biological activities, such as antitumor effects, cardiovascular protection, antibacterial or antiviral effects (Banerjee & Koketsu, 2017; Zhang et al, 2017; AlvarezPerez et al, 2018; Miao et al, 2018). We have developed an approach to the synthesis of [1,3]thia(selen,tellur)azolo[3,2-a]pyridin-4-ium derivatives via heterocyclization of unsaturated compounds and 2-pyridinesulfenyl, selenenyl and tellurenyl chlorides with ring closure through the nitrogen atom of the pyridyl fragment (Borisov et al, 2010, 2012a,b,c). In this case, our studies have paid particular attention to clarifying the structural characteristics of the reagents used (Borisov et al, 2010; Khrustalev et al, 2014, 2016). The product of this reaction was identified as 2,3,3a,9a-tetrahydro-1H-cyclopenta[4,5][1,3]selenazolo[3,2-a]pyridinium-9 bromide (2) by X-ray diffraction (Fig. 4)
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