Two six-coordinate Sn(IV) complexes, bis-[2,4,6,8-tetra-(tert-butyl)-9-oxyphenoxazinyl-1-onolate] Sn(IV) 4 and bis-[2,4,6,8-tetra-(tert-butyl)-phenoxazinyl-1-onolate] Sn(IV) dichloride 5 with redox-active tridentate 2,4,6,8-tetra(tert-butyl)-9-hydroxyphenoxazin-1-one 2 and bidentate 1-H-1-oxo-2,4,6,8-tetra(tert-butyl) phenoxazine-1-one 3 ligands were synthesized and their molecular structures determined with the use of X-ray crystallography. Electronic structures of the complexes were investigated with DFT B3LYP*/6-311++ G(d,p) calculations, SQUID magnetometry and EPR spectroscopy and assigned to the biradical Sn(IV)(CatNSQ)(2) and Sn(IV)(ISQ)(2)Cl-2 electromeric forms, where (CatNSQ)(2) and (ISQ) are radical-anions formed by the ligands 2 and 3, correspondingly. Weak ferromagnetic coupling of the two paramagnetic centers was established in complex Sn(IV)(CatNSQ)(2) with ligands 2, whereas in the same type complex formed by ligands 3 the coupling of the paramagnetic centers bears weak antiferromagnetic character. The calculated exchange coupling constants J for 4 and 5 (5 cm(-1) and -8 cm(-1), respectively) are in sufficiently good agreement with the values obtained from analysis of mu(eff)(T) dependences (3.5 cm(-1) and -1 cm(-1)).