Magnetic Property Modulation Tuned by Ligand Diversity in Tetranuclear {Ni ₄ O ₄ } Cubane Complexes

The rigid {Ni4O4} cubane framework serves as a key structural motif for modulating magnetic exchange through μ3-oxo bridges, enabling precise correlations between the Ni–O–Ni geometry and magnetic behavior. In this report, a series of five tetranuclear nickel(II) cubane complexes 1–5, supported by structurally diverse Schiff base and o-vanillinate ligands, have been synthesized and fully characterized by single-crystal X-ray diffraction, spectroscopy, and magnetic measurements. All complexes exhibit a common {Ni4O4} cubane core but display distinct coordination environments arising from subtle variations in ligand donor sets and solvent/anion binding, leading to significant modulation of Ni–O–Ni angles and Ni···Ni separations. All investigated complexes exhibit a pronounced easy-plane anisotropy of NiII ions (positive D-parameter). Although ferromagnetic exchange interactions dominate within the cubane core, the magnetic moment at low temperatures is diminished due to the competing effects of antiferromagnetic exchange interactions and easy-plane anisotropy. In complex 4, one of the NiII ions coordinated by a nitrate ligand possesses a small negative anisotropy parameter (predicted as D = −2.96 cm–1). In complex 1, a low temperature, long-range magnetic order emerges, driven by intermolecular hydrogen bonding through coordinated water molecules. Collectively, the results show that minor ligand modifications allow controlled tuning of magnetic exchange and anisotropy in NiII cubane clusters, providing useful design guidelines for 3d-metal molecular magnetic materials.