The structure of dimeric 2,7-bisij4-(trifluoromethyl)phenyl]-4λ4,5λ4,9λ4,10λ4-tetrathietoij1,2-a:3,4-a′]bis [1,2,3,5]dithiadiazole (C8H4F3N2S2)2 and its adduct with triphenylstibin (C8H4F3N2S2)2·C18H15Sb, both have triclinic (P¯1) symmetry. They crystallize in layers containing centrosymmetric clusters consisting of four dithiadiazolyl dimers in the parent compound and two such dimers paired with two triphenylstibine units in the aromatic co-crystal. In the co-crystal, the Ph3Sb molecules associate with an equivalent moiety from a neighbouring cluster in a geometry that is very reminiscent of other Ph3Sb-containing structures. Thus, the adduct combines structural elements from those of its component parts. Key interactions between molecules in the pure dithiadiazolyl (S to S) and the co-crystal (S to C) are significantly shorter than the sums of atom van der Waals radii.