A K[Ni(NH3)6]2.5[Re12CS14(μ-O)2(μ-SO2)(CN)6]·8H2O compound (1) with a new [Re12CS14(μ-O)2(μ-SO2)(CN)6]6– cluster anion is prepared by the interaction of [Ni(NH3)6] (aq) 2+ with the products of incomplete substitution of μ-SO 2 2− ligands in the [Re12CS14(μ-SO2)3(CN)6]6– cluster anion and structurally characterized. New data on the effect of the ionic radius of the bridging μ-Q ligands on the geometric characteristics of the prismatic central {Re3C(μ-Q)3Re3} unit of the bioctahedral cluster anions are obtained. The synthesis of compound 1 experimentally confirms the existence of stable intermediates in the μ-O2– substitution reaction for the μ-SO 2 2− ligands of the [Re12CS14(μ-SO2)3(CN)6]6– anion and evidences that the reaction proceeds in steps.