Insights into the structural chemistry, topology, and complexity of organically templated polychromates(VI) with the linear [CrnO3n+1]2– groups: Synthesis and crystal structures of 1-methylpiperazinium polychromates, (C5H14N2)Cr2O7 and (C5H14N2)Cr3O10

Single crystals of two new compounds, (C₅H₁₄N₂)Cr₂O₇ (1) and (C₅H₁₄N₂)Cr₃O₁₀ (2), were isolated from the reaction products of 1-methylpiperazine and chromium trioxide in aqueous media. The crystal structures have been studied by the means of single-crystal X-ray analysis. The unit cell parameters are: a = 7.8459(1) Å, b = 8.8295(1) Å, c = 15.8951(2) Å, β = 96.634(1)°, space group P2₁/n for 1 and a = 8.0620(2) Å, b = 11.6652(4) Å, c = 14.5690(5) Å, β = 100.285(3)°, space group P2₁/c for 2. In contrast to chromate compounds templated by structurally related ethylenediammonium and piperazinediium cations, no monochromate was found in the 1-methylpiperazine – water – chromic oxide system. Both structures can be represented as nets of hydrogen bonds between the organic ammonium cations and polychromate anions. We discuss the structural features of various polychromate species (Cr₂O₇²⁻, Cr₃O₁₀²⁻, and Cr₄O₁₃²⁻) among structures comprising organic and inorganic cations.