Tuning of Jahn-Teller distortions via sterically enforced lattice enlargement of Cu(ta)2-type coordination polymers

The control of Jahn-Teller distortions in copper-based coordination polymers is crucial for tuning their magnetic and structural properties. Here, we report the synthesis and characterization of two novel Cu(II)-based metal-organic frameworks (MOFs), Cu(mta) 2 and Cu(cta) 2 , derived from modified triazole ligands. By introducing steric bulk through methyl and cyclopentyl substituents, we systematically investigate the effect of lattice enlargement on local coordination environments and magnetic behaviour. Single-crystal and powder X-ray diffraction analyses reveal that Cu(mta) 2 exhibits static Jahn-Teller distortions similar to those observed in Cu(ta) 2 , whereas Cu(cta) 2 crystallizes in an undistorted, near-ideal cubic structure. Magnetic susceptibility and electron spin resonance measurements show strong antiferromagnetic interactions and temperature-dependent g-factor anisotropy for Cu(ta) 2 and Cu(mta) 2 , while Cu(cta) 2 displays nearly isotropic magnetic behavior and only dynamically JT distortions without a cooperative phase transition. These results demonstrate that steric ligand design offers a powerful strategy to modulate the interplay between lattice structure and magnetic anisotropy. Our findings provide fundamental insights into the suppression of cooperative static Jahn-Teller distortions and open pathways for the targeted design of multifunctional MOFs with tailored structural and magnetic properties. • Synthesis and characterization of the two novel metal-organic frameworks Cu(mta) 2 and Cu(cta) 2 , featuring Cu(II) condensed Kuratowski SBUs. • Increasing the steric volume of the ligands controls Jahn-Teller distortions by stiffening the lattice. • Cu(mta) 2 exhibits a static distortion without a clear phase transition. • Cu(cta) 2 exhibits a dynamic Jahn-Teller distortions which starts to slow down upon cooling, but no cooperative structural transition was observed via PXRD. • Simultaneous fitting of magnetic susceptibility and magnetization data agree with the data from ESR spectroscopy • Thermal and structural stability verified by VT-PXRD, TGA