Jansen's interests focus on basic research in the field of preparative solid state chemistry with the goal of developing modern materials. Classes of materials currently under investigation include new binary and ternary oxides, superconducting oxides, ionic conductors, structural oxide-ceramics and pigments, endohedral fullerenes and fullerides or amorphous inorganic nitridic networks. Besides employing traditional solid state synthesis methods, a large number of alternative techniques is used, e.g., the sol-gel-process, synthesis under high pressure, via an rf-furnace, at low temperatures in liquid ammonia, or by electrochemical methods. In addition, their chemical and physical properties, in particular optical, electrical and magnetic behavior, are analyzed. This provides the basis for placing the results in the proper context regarding structure-property-relationships and modern concepts of bond-theory. A long-term goal is to increase the predictability of solid state chemistry, i.e., to predict the existence of not-yet-synthesized compounds, calculate their properties, and finally provide prescriptions for their synthesis. This work involves both theoretical and synthetic aspects; on the theoretical side, structure candidates are determined using global optimization techniques, while on the preparative side kinetically controlled types of reactions are being developed.