The reflux of mononuclear ruthenium precursor [RuII(acac)2(CH3CN)2] (acac = acetylacetonate) in 2-methyl-2-propanol formed the novel diamagnetic β-diketonato ruthenium tetranuclear complex [Ru(μ-acac)2(μ3-O)2Ru3(acac)6] (1), in which was contained the deltoid core, [Ru4(μ3-O)2]8+, consisting of four ruthenium and two oxygen atoms. The complex 1 has been characterized on the basis of elemental analysis, 1H NMR, 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 γ-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 [Ru4(μ3-O)2]8+ core.