From an antiferromagnetic insulator to a strongly correlated metal in square-lattice MCl₂(pyrazine)₂ coordination...

Electronic synergy between metal ions and organic linkers is a key to engineering molecule-based materials with a high electrical conductivity and, ultimately, metallicity. To enhance conductivity in metal-organic solids, chemists aim to bring the electrochemical potentials of the constituent metal ions and bridging organic ligands closer in a quest to obtain metal-d and ligand-π admixed frontier bands. Herein, we demonstrate the critical role of the metal ion in tuning the electronic ground state of such materials. While VCl₂(pyrazine)₂ is an electrical insulator, TiCl₂(pyrazine)₂ displays the highest room-temperature electronic conductivity (5.3 S cm^-1) for any metal-organic solid involving octahedrally coordinated metal ions. Notably, TiCl₂(pyrazine)₂ exhibits Pauli paramagnetism consistent with the specific heat, supporting the existence of a Fermi liquid state (i.e., a correlated metal). This result widens perspectives for designing molecule-based systems with strong metal-ligand covalency and electronic correlations.