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.
Achieving high conductivity in metal-organic solids can be challenging, due to the difficulty of obtaining a good overlap between the d-orbitals of the metal and the π-orbitals of the organic molecule. Here, the authors present two coordination solids, VCl2(pyrazine)2 and TiCl2(pyrazine)2, with remarkably different electrical conductivity. While the former is an insulator, the latter displays the highest conductivity of any octahedrally coordinated metal ions based metal-organic solid.