Organometallic chemistry meets crystal engineering to give responsive crystalline materials

Abstract

Dynamically porous crystalline materials have been obtained by engineering organometallic molecules. This feature article deals with organometallic wheel-and-axle compounds, molecules with two relatively bulky groups (wheels) connected by a linear spacer. The wheels are represented by half-sandwich Ru(II) moieties, while the spacer can be covalent or supramolecular in character. Covalent spacers are obtained using divergent bidentate ligands connecting two [(arene)RuX₂] groups. Supramolecular spacers are instead obtained by exploiting the dimerization of COOH or C(O)NH₂ groups appended to N-based ligands. A careful choice of ligand functional groups and X ligands leads to the isolation of crystalline materials with remarkable host–guest properties, evidenced by the possibility of reversibly capturing/releasing volatile guests through heterogenous solid–gas reactions. Structural correlations between the crystalline arrangement of the apohost and the host–guest compounds allow us to envisage the structural path followed by the system during the exchange processes.