From an antiferromagnetic insulator to a strongly correlated metal in square-lattice MCl<sub>2</sub>(pyrazine)<sub>2</sub> coordination solids.

Perlepe, Panagiota; Oyarzabal, Itziar; Voigt, Laura; Kubus, Mariusz; Woodruff, Daniel N; Reyes-Lillo, Sebastian E; Aubrey, Michael L; Négrier, Philippe et al. · Nat Commun · 2022

basic_science · Level V

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Abstract

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 VCl<sub>2</sub>(pyrazine)<sub>2</sub> is an electrical insulator, TiCl<sub>2</sub>(pyrazine)<sub>2</sub> displays the highest room-temperature electronic conductivity (5.3 S cm<sup>-1</sup>) for any metal-organic solid involving octahedrally coordinated metal ions. Notably, TiCl<sub>2</sub>(pyrazine)<sub>2</sub> 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.