The fundamental objective of the present project was the elaboration of the strategy for the rational design of new materials with switching magnetic and optical properties perspective for their use as elementary base of nanoelectronics. In spite of the richness of the available experimental data the possibility of the elaboration of such synthetic strategy has been strongly constrained due to the lack of an adequate theoretical description of these materials. The present project included two subprojects, with the first subproject dealing with switchable materials demonstrating charge transfer induced spin transitions or redox induced electron transfer and the second one being devoted to the study of  spin crossover iron complexes with mixed ligand nitrogen-sulfur surrounding and 1D coordination polymers demonstrating spin transitions or ferromagnetic ordering. We planed to develop general theoretical models and approaches for the explanation of the unusual magnetic and spectroscopic properties of these fascinating systems. These models was properly take into account electron transfer, superexchange, vibronic coupling and cooperative interactions in the case of extended systems. The results of theoretical calculations was used for explanation of the experimental data of the technical advisers of the present project.