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Abstract

The following coordination compounds of cobalt(II) with 1-phenyl-4,6-dimethylpyrimidine-2-thione: CoLX₂ . n H₂O ( X = Cl^-, n = 1; X = Br^-, n = 2; X =SCN^-, n = 0; X = NO₃^-, n = 4), Co₂L₃Cl₄ . H₂O, CoL₂X₂ (X = Br^-, I^-, SCN^-, NO₃^-), CoL₂X₂ . n H₂O . p Me₂CO (X = I^-, ClO₄^-, n = p = 2; X = NO₃^-, n = 1, p = 0), CoL₃(ClO₄)₂ . 0.5 Me₂CO, Co₂L₅(NO₃)₄ and Co₂L₇X₄ (X = Cl^-, Br^-, I^-) have been isolated and characterized by chemical analyses, visible and IR spectra, paramagnetic susceptibility, conductivity and polarographic measurements. Solid phase IR spectra suggest that the heterocyclic ligand is almost always bonded through non-substituted ring nitrogen and exocyclic sulfur atoms. The solid compounds with the exception of the [CoL(SCN)₂]₂, [CoL₂(H₂O)₂][CoCl₄] and [CoL₃][CoCl₄] . H₂O have originally a distorted octahedral geometry. By grinding the solid [CoL₂(SCN)₂], Co₂L₇Cl₄ and all the bromide complexes the cobalt(II) coordination undergo octahedral (T> tetrahedral geometry change. Spectral evidences and polarographic results in DMF solution have shown that for these and [CoL(SCN)₂]₂, [CoL₂(H₂O)₂][CoCl₄] and [CoL₃][CoCl₄] . H₂O complexes, the solvolysis gives rise to equilibria between tetrahedral anionic [CoX₄]^2- (X = SCN^-, Cl^-), [CoX₃(DMF)]^- (X = SCN^-, Cl^-, Br^-) and some possible [Co(DMF)₆]²⁺, [CoX(DMF)₅]⁺, [CoXL(DMF)₄]⁺, [CoL(DMF)₅]²⁺ (L = N-monodentate ligand) cationic octahedral species. Polarographic data for perchlorate complexes and for [Co(DMF)₆](ClO₄)₂-L system at increasing ligand concentration have shown that in DMF solution the solved ions [Co(DMF)₆]²⁺ are the prevailing species and that the thiopyrimidine-containing species [CoL(DMF)₅]²⁺ (β = 3.78 . 10⁵) and [CoL₂(DMF)₄]²⁺ (β =9.59 . 10⁷) can be formed only in presence of large excess of the free ligand.