Reaction of the potassium salts of N-thiophosphorylthioureas RC(S)NHP(S)(OiPr)2 (R = Me2N, HLI; 2-MeC6H4NH, HLII; 2,6-Me2C6H3NH, HLIII; 2,4,6-Me3C6H2NH, HLIV) with Co(II) cations in aqueous EtOH leads to the complexes [Co(LI-IV-S,S')2] ([CoLI-IV2]). The structures of the complexes were studied by IR, UV-Vis spectroscopy and microanalysis. The crystal and molecular structure of [CoLI2] was elucidated by single crystal X-ray diffraction. The metal center is found in a tetrahedral S4 environment formed by the C=S and P=S sulfur atoms of two deprotonated ligands LI. Magnetic properties of [CoLI2] were also investigated.