Noninnocent Ligands as a Design Strategy for Fully Compensated Ferrimagnetism in Two-Dimensional Metal-Organic...

Fully compensated ferrimagnets (fFiMs), which combine vanishing macroscopic magnetization with spin-split electronic states, are attractive for stray-field-free spintronics. However, achieving exact moment cancellation typically requires fine control over inequivalent magnetic sublattices, making the rational design of fFiMs a fundamental challenge. Here, we propose a general design strategy for two-dimensional (2D) fFiMs by integrating redox-active noninnocent ligands (NILs) into metal-organic frameworks (MOFs). First-principles calculations demonstrate that fractional metal-to-ligand charge transfer converts NILs from closed-shell linkers into a spin-bearing ligand sublattice that aligns antiparallel to the metal centers, enabling stoichiometric moment compensation. We validated this concept in a family of trigonal 2D chromium MOFs. While the prototype Cr(BTT)2 confirms fully compensated ferrimagnetism, it exhibits intrinsic thermal instability. The modular nature of the NIL strategy allows for chemical refinement, and ligand fluorination (Cr(F-BTT)2) or heavy-chalcogen substitution (Cr(BSeT)2) stabilizes the 2D lattice without disrupting the fFiM ground state. The chemically optimized Cr(F-BTT)2 retains fully compensated ferrimagnetism and exhibits a near-Fermi quasi-Dirac-like band feature with an estimated magnetic transition temperature of 132 K. Extended studies of nitrogen- and phosphorus-based ligands further support the generality and boundary of this approach. These findings establish NIL-directed charge transfer as a chemically programmable handle for engineering 2D-compensated magnets.