pH-Dependent formation of (6,3) and (10,3) hydrogen-bonded networks based on [Ru(H2biim)3]SO4: polymorphs and topological isomers

Abstract

Two polymorphs formulated as [Ru(H2biim)3]SO4 (H2biim = 2,2′-biimidazole) have been solvothermally synthesized through changing the pH value of the reaction solution in an identical solvent at 120 °C. The α-[Ru(H2biim)3]SO4 (1) crystallizes in the monoclinic space groupP21/c with a = 8.1802(9) Å, b = 21.293(2) Å, c = 15.2116(14) Å, β = 121.357(4)°, Z = 4. The β-[Ru(H2biim)3]SO4 (2) crystallizes in a chiral space groupI41 with a = 12.6267(10) Å, c = 14.244(2) Å, Z = 4. Complex 1 assembles into homochiral (Δ and Λ), (6,3) honeycomb two-dimensional layers, which further alternately stack in racemic, hydrogen-bonded networks, whereas 2 is a chiral, (10,3)-b 3-D network. Thus 1 and 2 are topological isomers. Importantly, their formations are much dependent on the pH value of the reaction solution. The data observed in this study seem to suggest that the diverse hydrogen bonding modes between the sulfate and H2biim ligand identified here play a crucial role in the formation of the polymorphs and topological isomers. The powder XRD patterns and infrared spectra also provide valuable information in the diagnosis of the polymorphs.