High-resolution structural study on pyri­din-3-yl ebselen and its N-methyl­ated tosyl­ate and iodide derivatives

The crystal structure of the pyri­dine-substituted benzisoselenazolinone 2-(py­ri­din-3-yl)-2,3-di­hydro-1,2-benzoselenazol-3-one (C(12)H(8)N(2)OSe, 2), related to the anti­oxidant ebselen [systematic name: 2-phenyl-1,2-benzoselenazol-3(2H)-one, 1], is characterized by strong inter­molecular N⋯Se(—N) chalcogen bonding, where the N⋯Se distance of 2.3831 (6) Å is well within the sum of the van der Waals radii for N and Se (3.34 Å). This strong inter­action results in significant lengthening of the inter­nal N—Se distance, consistent with significant population of the Se—N σ* anti­bonding orbital. Much weaker inter­molecular O⋯Se chalcogen bonding occurs between the amide-like O atom in 2 and the less polarized C—Se bond in this structure. Charge density analysis of 2 using multipole refinement of high-resolution data allowed the electrostatic surface potential for 2 to be mapped, and clearly reveals the σ-hole at the extension of the Se—N bond as an area of positive electrostatic potential. Topological analysis of the electron-density distribution in 2 was carried out within the Quantum Theory of Atoms in Mol­ecules (QTAIM) framework and revealed bond paths and (3,−1) bond critical points (BCPs) for the N⋯Se—N moiety consistent with a closed-shell inter­action; however, the potential energy term is suggestive of electron sharing. Analysis of the electron localization function (ELF) for the strong N⋯Se and the weak O⋯Se chalcogen-bonding inter­actions in the structure of 2 suggest significant electron sharing in the former inter­action, and a largely electrostatic inter­action in the latter. Conversion of 2 to its N-methyl­ated derivatives by reaction with methyl iodide [1-methyl-3-(3-oxo-2,3-di­hydro-1,2-benzoselenazol-2-yl)pyri­din-1-ium iodide, C(13)H(11)N(2)OSe(+)·I(−)] and methyl tosyl­ate [1-methyl-3-(3-oxo-2,3-di­hydro-1,2-benzoselenazol-2-yl)pyri­din-1-ium toluene­sulfonate trihydrate, C(13)H(11)N(2)OSe(+)·C(7)H(7)O(3)S(−)·3H(2)O] removes the possibility of N⋯Se chalcogen bonding and instead structures are obtained where the iodide and tosyl­ate counter-ions fulfill the role of chalcogen-bond acceptors, with a strong I(−)⋯Se inter­action in the iodide salt and a weaker p-Tol-SO(3) (−)⋯Se inter­action in the tosyl­ate salt.