Interplay of Redox Non-Innocence and Symmetry Breaking in a 4d Coordination Framework

Incorporating 4d and 5d metal ions into coordination frameworks offers a powerful route to quantum materials where orbital delocalization and spin–orbit coupling reshape magnetic and electronic ground states. Yet, such systems remain largely unexplored. We introduce Mo(pyz)2I2, a pyrazine-linked square-lattice material that uniquely couples a paramagnetic heavy transition metal center with ligand-radical character, opening access to spin–orbit-entangled ground states in molecular frameworks. Structural and spectroscopic analyses establish a MoIII({pyz2}⦁−)I2 formulation, revealing pronounced ligand redox non-innocence and local symmetry breaking arising from a disordered distribution of neutral and reduced pyrazine linkers. Magnetization measurements reveal dominant antiferromagnetic interactions, while the electrical transport follows semiconducting Arrhenius behavior. Density functional calculations confirm strong Mo–pyz exchange and weak interlayer coupling. These results demonstrate how extending pyrazine frameworks to the 4d block profoundly modifies their redox and magnetic landscapes, establishing Mo(pyz)2I2 as a prototype for designing correlated and spin–orbit-entangled states in molecule-based quantum materials.