Driving the Assembling of Zirconium Tetraoxalate Metallotectons and Benzimidazolium Cations: From Three Dimensional Hydrogen-Bonded Compact Architectures to Open-Frameworks

Charge-assisted H-bond associations between [Zr(C₂O₄)₄]⁴⁻ preformed anionic complexes and several ditopic monocations based on the benzimidazolium motif ([H₂-Bim]⁺ cations) have been envisioned for the tentative elaboration of 3D H-bonded and open-framework architectures. Reactions involving [Zr(C₂O₄)₄]⁴⁻ units and [H₂-Bim]⁺ cations in (a) a charge stoichiometric amount, (b) a defect, and (c) an excess of cation afforded three different compounds of formula {(H₂-Bim)₄[Zr(C₂O₄)₄]}·H₂O (1), {K(H₂O)(H₂-Bim)₃[Zr(C₂O₄)₄]}·2H₂O (2), and {(H₂-Bim)₄[Zr(C₂O₄)₄]} (3), respectively. Structural analyses revealed marked differences in their formulations and in their supramolecular connectivities. These results traduce the importance of cation concentration on the association schemes. Among them, compound 3 exhibits a chiral structure analyzed as resulting from the interpenetration of two 3D H-bonded homochiral and independent networks. To avoid this interpenetration and to study the influence of the cation substitution for fixed experimental parameters, 2-amino and 2-methyl substituted [H₂-Bim]⁺ cations ([H₂-2-NH₂Bim]⁺ and [H₂-2-MeBim]⁺, respectively) have been envisioned as cationic building-blocks. Structure analysis for the corresponding materials ({(H₂-2-NH₂Bim)₄[Zr(C₂O₄)₄]} (4) and {(H₂-2-MeBim)₄[Zr(C₂O₄)₄]}·7H₂O (5), respectively) revealed that the amino group contributes in the H-bonded framework, whereas the methyl impairs the formation of H-bonds between the cations and the anions. These observations contribute to explain the marked structural differences between 3 and these two networks. With 5-methyl- and 5-chlorobenzimidazolium cations ([H₂-5-MeBim]⁺ and [H₂-5-ClBim]⁺, respectively), [Zr(C₂O₄)₄]⁴⁻ is converted into its binuclear version, [Zr₂(C₂O₄)₇]⁶⁻, yielding {(H₂-5-MeBim)₆[Zr₂(C₂O₄)₇]}·3H₂O (6) with a close-packed 3D-network and {(H₂-5-ClBim)₆[Zr₂(C₂O₄)₇]}·13.5H₂O (7) with an open-framework architecture (potential solvent accessible void volume of 23%). For 7, Cl···π interactions contribute to the cohesion of the 3D supramolecular architecture.