Construction of hydrogen-bonded networks of 1′,1‴-diboronic acids of biferrocene and biferrocenium cation

Abstract

The solid-state structures of 1′,1‴-biferrocenediboronic acid (1) were elucidated by X-ray crystallography, to obtain insight into controlling the structures of hydrogen-bonded (H-bonded) assemblies from a functional organobimetallic building block. Four solvated crystal forms of 1 were newly obtained by recrystallization under different solvent conditions. The dioxane-, pyridine-, and pyrimidine-solvated crystals (Forms III to V) involved chain-like 1D H-bonded networks of 1. The 1D chains of 1 were capped with solvent molecules with lateral H-bonds. The pyrazine-solvated crystals (Form VI) involved 1D chains of 1, which were connected by pyrazine molecules with lateral H-bonds to afford sheet-like 2D networks. The suitable bidentate H-bond acceptor was found to transform 1D chains into 2D networks. Two crystal forms of 1′,1‴-biferroceniumdiboronic acid (1+) were also prepared and investigated the geometry of the H-bonded assemblies and the valence states of 1+. The mixed-valence (MV) cation 1+ forms 1D chains (Form VII) and discrete dimers (Form VIII) with triiodide anions in the valence-detrapped and trapped states, respectively. This study demonstrates the usefulness of the boronic acid-based method to obtain MV supramolecular structures in the solid state.