selenide (1), ethynyl 2-(methylselenyl)benzyl selenide (2), and 2-(methylselenyl)benzyl selenocyanate (3). By means of NMR spectroscopic studies we have determined the 77Se NMR chemical shifts of the signals of the Se centers of 1–3 and their long-range 4JSe,Se couplingconstants. These results, and the X-ray structural studies of single crystals of 3 and 11, a quasi-dimer of 2, point to an Se···Se van der