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

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Abstract
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)2I2, 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 MoIII({pyz2}•-)I2 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)2I2 as a prototype for designing correlated and spin-orbit-entangled states in molecule-based quantum materials based on heavier transition metals.
Funding Information
  • Danmarks Grundforskningsfond (DNRF189)
  • Ministerio de Ciencia, Innovaci?n y Universidades (CEX2023-001286-S)
  • Ministerio de Ciencia, Innovaci?n y Universidades (PID2024-159457OB-C21)
  • Universidad Andr?s Bello (DI-02-25/ATP)
  • European Regional Development Fund (CEX2023-001286-S)
  • European Regional Development Fund (PID2024-159457OB-C21)
  • Danmarks Frie Forskningsfond (0165-00073B)
  • Novo Nordisk Fonden (0085640)
  • Villum Fonden (42094)
  • Carlsbergfondet (CF17-0637)
  • Agencia Nacional de Investigaci?n y Desarrollo (1220986)

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