The title material, where TM-TPDS is 2-[4,5-bis(methylthio)-1,3-diselenol-2
-ylidene]-5-(thiopyran-4-ylidene)-1,3,4,6-tetrathiapentalene, has three-dim
ensional (3D) donor array, in which 1D donor columns are tetragonally arran
ged with each other. It shows metal-like conducting behavior down to T-MI =
100 K.