Isomeric chain structures of {[Mn(H2O)4]2Ru2(CO3)4Br2}nn−: syntheses, structural diversity and magnetic properties

Abstract

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)₄Br₂⁵⁻ units are linked by two disubstituted octahedral Mn(H₂O)₄²⁺ 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 H_C = ∼1.2 kOe at 2.0 K.