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The self-assembly of Ru2(CO3)43- paddle-wheel precursors and Mn2+ ions in aqueous solution yields various carbonate complexes. With appropriate selection of the synthetic conditions, we are able to intentionally tune the composition and structure of Mn-Ru2-carbonate assemblies to form infinite chain structural complexes, e.g., K[{Mn(H2O)4}2Ru2(CO3)4Br2]·H2O (1) and H[{Mn(H2O)4}2Ru2(CO3)4Br2]·6H2O (2). Complexes 1 and 2 are obtained at different temperatures (25°C for 1 and 5°C for 2, respectively), and their crystal structures consist of brick-wall stacked chains, in which neighboring Ru2(CO3)4Br2 5- units are linked by two disubstituted octahedral Mn(H2O)4 2+ in a cis manner, resulting in two isomeric (twisted and zigzag) negative double-chain α- and β-{[Mn(H2O)4]2Ru2(CO3)4Br2}nn-. The magnetic properties of complexes 1 and 2 were highly characterized. The alternating current (AC) susceptibility analysis of complex 1 reveals a two-step magnetism transition at T1 = 5.0 K and T2 = 2.6 K, respectively. Complex 2 exhibits metamagnetism behavior, with a transition field HC = ~1.2 kOe at 2.0 K. [ABSTRACT FROM AUTHOR]