Final Activity Report Summary - MAGNETX (Crystal Engineering of Molecular Magnets) Molecular magnetic materials may be ranged in two classes. One class comprises the so call molecule-based magnets (MBM) in which the spin carriers interact in a three-dimensional array in the solid state. They may be organic, organometallic or coordination compounds. While different at the atomic scale their magnetic behaviour is not different from the traditional magnets. Curie temperatures have been obtained at ambient for cyanide-bridged metal compounds; however, for most systems they are still low, in the best cases close to the liquid nitrogen temperature. The second class concerns the so-called single molecule magnets (SMM). Their magnetism is fundamentally different from the traditional magnets because in this case the molecules behave individually as isolated magnets. The social issues of molecular magnets are numerous. The aim of the development of molecular magnetic materials is to have novel magnetic materials for future applications in information process and storage. An interesting issue is also the possibility to have multifunctional materials by, for example, combining magnetism with optical properties. This research field is very active and comes closer and closer to applications but still requires strong basic research, in particular for the increase the Curie temperature of the MBM and the blocking temperature of the SMM. From the chemical point of view the rational assembling of the magnetic precursors, called spin carriers, into an assembly exhibiting spontaneous magnetisation is still a real challenge. From the physical and theoretical chemistry point of views there is a need for understanding the fine interplay between the electronic structure, the crystal structure and the physical properties. The work performed during the fellowship mainly concerned theoretical calculations to understand the magneto-structural relationships and the nature of the magnetic interactions in such systems. In order to do this, Dr Y. Chumakov based his calculations on X-ray crystallographic investigations. Spin density mapping by polarised neutron diffraction was also performed in relation with this work. Among important project results was the establishment of the magneto-structural correlation in two-dimensional manganese(II)-radical layered compounds and the rationalisation of the pressure effect in magneto-luminescent compounds.