Cobalt(II) perchlorate,tetrafluoroborate, nitrate and sulphate complexes with 4,6-dimethylpyrimidine-2(1H)-thione

Contrary to earlier reports in which no adducts of Co(II) metal ion with 4,6-dimethylpyrimidine-2(1H)-thione(HL) could be isolated starting from Co(ClO₄)₂ · 6H₂O, we now report bis- and tris-ligand Co(II) complexes of the type [Co(HL)₂(H₂O)₂]X₂ · H₂O (X = ClO₄, BF₄), [Co(HL)₂NO₃]NO₃, [Co(HL)₂SO₄] · 0.5H₂O and [Co(HL)₃]X₂ · 0.5H₂O (X = ClO₄, BF₄). They have been synthesized by refluxing 2:1 and 3:1 mixtures of HL and CoX₂ · nH₂O in ethanol-triethyl orthoformate. We also describe new Co(HL)₂X₂ · nH₂O complexes in which for X₂ = ClBr, ClI and BrI, n = 2; for X₂ = I₂, n = 1 and for X₂ = (SCN)₂, n = 0. Structural characterization of the complex species is made from electronic and vibrational spectra, magnetic susceptibility measurements in the solid state and conductivity measurements in DMF solution. The magnetic and electronic spectral data together with ligand-field parameters suggest a pseudo-octahedral environment for all the Co(II) complexes, with the exception of Co(HL)₂SO₄ · 0.5H₂O in which the Co(II) ion appears to be pentacoordinated. The IR spectra are consistent with a coordination involving N,S-chelation of the ligand through the non-protonated ring nitrogen atom and the exocyclic sulphur atom.