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. However, such systems remain difficult to access synthetically. Here we report Mo(pyz)I, the first pyrazine-bridged square-lattice framework featuring a paramagnetic 4d metal center, obtained using a new organometallic precursor route that enables Mo incorporation. Structural and spectroscopic data establish a Mo({pyz})I formulation and reveal pronounced ligand redox non-innocence accompanied by local symmetry breaking arising from a disordered distribution of neutral and reduced pyrazine linkers─the first experimental observation of local symmetry lowering in a pyrazine-based coordination solid. Magnetic measurements show strong antiferromagnetic interactions without clear evidence of long-range order, and electrical transport indicates narrow-gap semiconducting behavior. Extending pyrazine framework chemistry to the 4d block thus requires new synthetic strategies and reveals new local structural and magnetic degrees of freedom, positioning Mo(pyz)I as a prototype for designing correlated and spin-orbit-entangled states in molecule-based quantum materials based on heavier transition metals.