Self-Assembly of Zr(C₂O₄)₄^4– Metallotectons and Bisimidazolium Cations: Influence of the Dication on H-Bonded Framework Dimensionality and Material Potential Porosity

Abstract

Assemblies involving [Zr(C₂O₄)₄]^4– metallotectons (C₂O₄^2– = oxalate) and linear, flexible, or V-shaped organic cations (H₂-Lx)²⁺ derived from the 1,4-bisimidazol-1-ylbenzene molecule have been envisioned to elaborate porous frameworks based on ionic H-bonds. Five architectures of formula [{(H₂-L1)₂Zr(C₂O₄)₄}·2H₂O] (<b>1</b>), [{(H₂-L2)₂Zr(C₂O₄)₄}·6H₂O] (<b>2</b>), [{(H₂-L3)₂Zr(C₂O₄)₄}·6H₂O] (<b>3</b>), [{(H₂-L4)₂Zr(C₂O₄)₄}·H₂O] (<b>4</b>), and [{(H₂-L5)₂Zr(C₂O₄)₄}·6H₂O] (<b>5</b>) (with L1 = <i>p</i>-bis(imidazol-1-yl)benzene, L2 = <i>p</i>-bis(2-methylimidazol-1-yl)benzene, L3 = <i>p</i>-bis(imidazol-1-yl)-2,5-dimethylbenzene, L4 = <i>p</i>-bis(imidazol-1-ylmethyl)benzene, L5 = <i>m</i>-bis(imidazol-1-yl)benzene) have been obtained; <b>1</b>–<b>3</b>, and <b>5</b> show an open-framework. For all, the bisimidazolium cations (H₂-Lx)²⁺ act as bridges between anionic complexes. Depending on the chemical features of the cation, various assembling patterns have been observed, yielding one-dimensional (1D) (<b>2</b>, <b>5</b>) two-dimensional (2D) (<b>1</b>), or three-dimensional (3D) (<b>3</b>, <b>4</b>) H-bonded networks. While interconnection of anionic metallotectons and organic cations generally affords grids with large apertures, 2D and 3D H-bonded frameworks show the lowest potential porosities (and even compact architectures) because of interpenetration. Highest potential solvent accessible voids (up to 20%) are found for the 1D H-bonded assemblages because interpenetration does not occur for these materials. Crystal structures for all five architectures as well as their thermal stabilities are reported. Actual porosity has been evidenced for one of them by solving the structure of the guest free architecture