The reflux of mononuclear ruthenium precursor [Ru-II(acac)(2)(CH3CN)(2)] (acac = acetylacetonate) in 2-methyl-2-propanol formed the novel diamagnetic beta-diketonato ruthenium tetranuclear complex [Ru(mu-acac)(2)(mu(3)-O)(2)Ru-3(acac)(6)] (1), in which was contained the deltoid core, [RU4(mu(3)-O)(2)](8)+, consisting of four ruthenium and two oxygen atoms. The complex 1 has been characterized on the basis of elemental analysis, (HNMR)-H-1, structural and cyclic voltammetric analyses. The molecular structure of 1 showed that each ruthenium ion was bridged by two oxygen atoms and two ruthenium ions link to gamma-carbon on acetylacetonate coordinated to another ruthenium. The cyclic voltammogram of 1 showed two reversible one-electron oxidation peaks and an one-electron reduction peak corresponding to the redox of [Ru-4(mu(3)-O)(2)](8)+ core.