Heterospin complexes based on cobalt semiquinolate with stable nitroxides of composi tion [Co(SQ) 2 (NIT) 2 ]•8CH 2 Cl 2 , [Co(SQ) 2 (NIT) 2 ]•4MeCN, [Co(SQ) 2 (IN) 2 ]•5Me 2 CO, [Co(SQ) 2 (IN) 2 ]•4MeCN, and [Co(SQ) 2 (IN) 2 ]•2CH 2 Cl 2 •C 6 H 14 , where SQ is 3,6 di tert butyl o benzosemiquinolate, NIT is 4,4,5,5 tetramethyl 2 (1 methyl 1H imidazol 5 yl) 4,5 di hydro 1H imidazole 3 oxide 1 oxyl, and IN is the imine analog of NIT, viz., 4,4,5,5 tetra methyl 2 (1 methyl 1H imidazol 5 yl) 4,5 dihydro 1H imidazole 1 oxyl, were synthesized. The characteristic feature of these compounds is that they contain two different types of para magnetic organic ligands. The X ray diffraction study showed that the solid phases of the complexes have a molecular structure. According to the data from thermomagnetic analysis (2-350 K), all complexes exhibit effects of valence tautomerism at ~20 °C. It was found that incorporated solvent molecules have an effect on the magnetic anomaly temperature.The design of new types of magnetically active com pounds requires the development of methods for the di rected construction of highly efficient exchange coupled multispin ensembles. 1-15 One of approaches to the syn thesis of such ensembles is based on the use of heterospin compounds, viz., transition metal complexes with organic radicals, 15-32 whose molecules contain paramagnetic cen ters of different nature with unpaired d (or f) and p elec trons. Metal complexes with nitroxides 15-33 and o semi quinone (o iminosemiquionone) metal complexes 34-37 comprise the most representative classes of such com pounds. Many complexes belonging to these classes can be magnetized in the solid state. 15,16,18-20,25,28-32 Known synthetic approaches provide a way to prepare magneti cally active compounds containing simultaneously a stable organic radical and two or more paramagnetic metal centers. 28,31-33, 38 Both antiferro and ferromagnetic exchange interac tions can occur between the magnetic centers in heterospin transition metal complexes with o semiquinolate ligands. The geometry of the complexes is one of the factors that influence the character of these interactions, and the mag netic properties of the complexes can be controlled by varying the geometric parameters. The addition of neutral ligands to square planar low spin bis o semiquinone Ni II complexes affords high spin five or six coordinate com plexes. 39-41 Recently, it has been shown 41 that the reac tion of copper(II) bis(3,6 di tert butyl o benzosemiquino late) [Cu(SQ) 2 ] with neutral aza ligands is accompanied by the transformation of the geometry resulting in a con siderable change in the ratio of the ferro to antiferromag netic exchange in the [Cu(SQ) 2 ] matrix. In the cited study, the first heterospin Cu II complex with paramagnetic ligands of different nature, viz., the o semiquinone radical anion and stable 2 imidazoline nitroxide, was isolated and characterized. 41 In continuation of these investigations, we synthesized first heterospin complexes based on cobalt o semiquinola...