Organoselenium(II) halides containing the pincer 2,6-(Me2NCH2)2C6H3 ligand – an experimental and theoretical investigation

New organoselenium(II) halides of the type [RSe]+X− [R = 2,6-(Me2NCH2)2C6H3; X = Cl (2), Br (3), I (4)] were prepared by cleavage of the Se–Se bond in R2Se2 (1) with SO2Cl2 followed by halogen exchange when organoselenium chloride was treated with NaBr or KI. The reaction between 2 and R’2MCln resulted in new ionic [RSe]+[R’2MCln+1]− [R’ = 2-(Me2NCH2)C6H4, n = 1, M = Sb (5), Bi (6); R’ = Ph, M = Sb, n = 1 (7) or n = 3 (8)] species. All new compounds were investigated in solution by multinuclear NMR spectroscopy (1H, 13C, 77Se, 2D experiments) and mass spectrometry. The ionic nature of 2 and the antimonates species was confirmed by conductivity studies. The molecular structures of [{2,6-(Me2NCH2)2C6H3}Se]+Cl−·nH2O (2·H2O and 2·2H2O) and [{2,6-(Me2NCH2)2C6H3}Se]+[Ph2SbCl4]− (8), respectively, were established by single-crystal X-ray diffraction, pointing out that the ionic nature of these compounds is also preserved in the solid state, with both nitrogen atoms strongly trans coordinated to the selenium atom of the cation. Theoretical calculations carried out at the DFT level were exploited to investigate the nature of the bonding in compounds 2–4 and the free cation [RSe]+ (2a). A topological analysis based on the theory of Atoms-In-Molecules (AIM) and Electron Localization Function (ELF) jointly to a Natural Bond Orbital (NBO) approach was used to shed light on the effect of the nature of the halogen species X on the bonding within the 3c-4e N–Se–Nmoiety