Bis[(2-dimethylaminomethyl)phenyl] diselenide (RSe)₂ was obtained by the organolithium route. It underwent facile reaction with stoichiometric amounts of bromine and iodine to give the corresponding arylselenium halides RSeBr and novel RSeI in which the selenium is covalently bonded to iodine. With an excess of bromine it gave the corresponding tribromide RSeBr₃ but a similar reaction with iodine gave only RSeI. With diazomethane it gave the selenoether (RSe)₂CH₂ and with HCl the known bis(hydrochloride)(RSe)₂·2HCl. A catalytic conversion of alkenes into allylic acetates using (RSe)₂ was carried out. The compounds were characterised by elemental analyses, mass, multinuclear NMR (¹H, ¹³C, ⁷⁷Se), IR, Fourier-transform-Raman spectrometry and conductance measurements. The compound RSeBr₃ shows evidence for the existence of Se ⋯ N interaction in solution and was found to equilibrate between co-ordinated and non-co-ordinated forms. The structures of the diselenide (RSe)₂ and its bromo derivative RSeBr were determined by X-ray crystallography. The compounds are isostructural and exhibit Se ⋯ N intramolecular co-ordination. The Se atom has T-shaped three-co-ordination in both structures and the five-membered chelate rings formed by the Se, C and N atoms are puckered and exist in an envelope conformation. The Se ⋯ N interaction in RSeBr [Se–N 2.143(6)Å] is, however, considerably stronger than that in (RSe)₂[Se(1)–N(1) 2.856(3), Se(2)–N(2) 2.863(4)Å].