Synthesis, Crystal Structure, and Magnetic Properties of a Chiral Cyanide-Bridged Bimetallic Framework K₃[Mn^II(l‑asp)]₆[Cr^III(CN)₆]·2H₂O

All five coordinating atoms of the amino-acid dianion l-aspartate (l-asp = NH2CH­(COO)­CH2COO2–) are found to be involved in coordination with MnII in the presence of [CrIII(CN)6]3– to self-assemble into a chiral three-dimensional cyanide-bridged K3[Mn­(l-asp)]6[Cr­(CN)6]·2H2O containing the highest ratio of Mn:Cr of 6:1. It adopts the chiral P3 (no. 143) space group consisting of zigzag Mn–OCO–Mn chains sharing edges of hexagonal channels with central [Cr­(CN)6]3–, while K+ and H2O occupy another parallel star-shaped channel. Its magnetic susceptibility above 100 K is dominated by the nearest neighbor (Mn–Cr at 5.08 and 5.31 Å) antiferromagnetic (AF) exchange interactions (θ = −15(1) K) and below 40 K by further AF interaction between Mn and Mn at 5.32 Å. It finally reaches a steady value at 4.5 K, where a bifurcation of the zero-field-cooled and field-cooled magnetizations is observed in small fields (<1 kOe). The isothermal magnetization is linear in field and deviating toward saturation above 60 kOe at 2 K. No imaginary component of the ac susceptibilities is observed. This behavior is associated with long-range antiferromagnetic order of a helical or conic nature where the magnetic sublattices are numerous [2n × (6Mn + 1Cr)], leading to a domain of sufficient size to allow for the presence of the bifurcation. A model is proposed based on the local anisotropy and symmetry multiplicity of the space group.