The formation of the mixed-stack donor-acceptor complex of dithieno [3,2-b:2′,3′-d]thiophene (1) and trimeric perfluoro-ortho-phenylene mercury (I) has been investigated under different conditions. Two solvatomorphs - mixed-stack complexes with a 1:1 donor-acceptor ratio and different solvent molecules in the solid state (dichloromethane (2) and dichloroethane (3)) have been obtained and characterized by experimental methods (FT-IR spectroscopy, differential thermogravimetric analysis, and X-ray crystallography) and quantum-chemical calculations at the density functional theory level. The differences in the solid state packing, thermal stability and potential charge-transfer properties of 2 and 3 are discussed. © 2015, Elsevier B.V. All rights reserved.