Selenium(IV) undergoes reductive complexation with dithiocarbamate (r1/r2 N — CS2 = L) to give SeL2. The complexes prepared are with R1 = R2 = n propyl, isopropyl and R1R2N = piperidinyl. The crystal structure of bis(piperidinyl-dithiocarbamato)selenium(II) is reported. The crystals are monoclinic, space group P21/n with cell parameters a = 8.735(1), b = 11.530(2), c = 16.766(3) A, β = 100.58(1)°, F(000) = 816. Final R = 0.088 for 2879 unique reflections. The SeS4 core has a planar trapezoidal configuration. The dithiocarbamate ligands are present as unequal bidentates with one short Se—S [2.301(3) A] and long Se —S [2.785(3) A] bonds. The average Se — S bond distance 2.547(4) A is close to the average Se —S distance observed in four coordinated Se(II) — sulphur ligand complexes. © by R. Oldenbourg Verlag, München 1989