The finding some polynuclear complexes can behave like magnets on the molecular level attracted much attention, opening perspectives for their applications in processing devices or for high density information storage carriers. To manifest single-molecule magnet (SMM) behaviour a polynuclear complex should have a high-spin ground-state and strong negative anisotropy (D). The energy barrier, U, separating two spin orientations (up-down) is proportional to the product of │D│ and square of spin, S. Therefore the larger the D and S values are the higher the U barriers should be and the longer the magnetization might be blocked. However, such single-molecule magnetization is so far only observed at temperatures too low to allow an application.The project aims to rise the blocking temperature by increasing the U. Our approach is based on heterospin polynuclear complexes assembling involving orbitally-degenerated 4d, 5d metal centres (Os, Ru) and 3d metal ions or/and nitroxide radicals. If the utilisation of the first guaranties the strong anisotropy, the use of the stable radicals as ligands and bridges assures well isolated high spin ground-state owing to the strong exchange interactions between spin carriers. The synthesis work will be complemented with structural analysis and magnetic studies of these systems to elucidate the magnetic interactions as well the magnetic anisotropy in conjunction with theoretical magneto-structural analysis. A major goal of the project is to discover some rules for the rational design of polynuclear cluster systems with elevated blocking temperatures. The project results will document the coordination chemistry of 4d and 5d ions with nitroxides, a field lacking of fundamental results. The complexes will bring experimental opportunity to test and improve theoretical models. The project might be considered as a step toward molecular spintronics. Prototypes of devices could be envisioned if the right property shows up at liquid nitrogen.