Complexes containing a Ru(2)(n+) core (n = 4, 5 or 6) have been of great interest because of their variety of electronic configurations and magnetic properties. Herein, we report a novel homovalent Ru(2)(6+)-based complex, (H(2)pip)(2)[Ru(2)(hedp)(2)Cl(2)]·6H(2)O (pip = piperazine) (1), isolated by the direct reaction of the mixed-valent Ru(2)(5+)-based anion Ru(2)(hedp)(2)(3-) [hedp = 1-hydroxyethylidenediphosphonate, CH(3)C(OH)(PO(3))(2)] with oxidant peracetic acid under room temperature conditions. Magnetic measurements unambiguously confirm that this complex contains four unpaired electrons with a spin ground state of S = 2.