The synthesis and characterization of the first paramagnetic diruthenium(III) complex containing two unpaired electrons is described. The investigated compound, represented as Ru-2(hpp)(4)Cl-2, where hpp is 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinate ion, was obtained from the reaction of Ru-2(CH3-COO)(4)Cl with excess molten Hhpp under Ar (150 degrees C, 10 h). It was characterized by X-ray single-crystal diffraction, electrochemistry, ESR, and UV-visible spectroscopy and the data compared to that for other Ru-2(6+) derivatives containing either four unpaired electrons (in the case of a bis-H2O complex) or zero unpaired electrons (in the case of a bis-C=CC6H5 derivative).