A series of novel transition and rare-earth metal complexes of (Z)-4-((1-(benzo[d]thiazol-2-yl)-3-methyl-5-oxo-4,5-dihydro-1H-pyrazol-4-yl)diazenyl)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one (HL) were isolated and identified by FT IR, EPR, 1H NMR, and UV–VIS spectroscopy. The crystallographic data for [Cu2Cl3(L)(H2O)]2·1.5H2O·CH2Cl2 were obtained. The compound exists in the form of a tetranuclear species with two different metal coordination modes. The coordination polyhedra of two cations can be described as somewhat distorted tetragonal pyramids as well as two other Cu atoms of the tetrameric molecule adopt the trigonal bipyramidal coordination. The bridging chloride ligands link differently coordinated metal cations. The quantum chemical calculations indicate the existence of a ferromagnetic exchange interaction in pairs. That is in agreement with the EPR spectrum of the substance. The complex formation constants in water-ethanol solutions were determined. © 2017 Elsevier B.V.