Magneto-Structural Models Construction of Isostructural Co(II) and Ni(II) Complexes via DFT Guidance and Different Magnetic Properties Based on Ab Initio Calculations

Establishment of magneto-structural model remains a critical challenge in estimating various spin Hamiltonian parameters and magnetic exchange mechanisms in molecular magnets. Here we successfully synthesized two isostructural coordination polymers (CPs), namely, {[Co3(L)2(4,4′-bpy)2(H2O)2]·(H2O)4}n (1) and [Ni3(L)2(4,4′-bpy)2(H2O)2]n (2), by using 3-(2,4-dicarboxyphenyl)-4-carboxylpyridine (H3L) under solvothermal conditions. Meanwhile, the reasonable magneto-structural model has been determined via density functional theory (DFT) calculations, complex 1 exhibits antiferromagnetic (AFM) interactions based on the contribution of mononuclear Co(II), while complex 2 shows ferromagnetic (FM) coupling mainly from binuclear Ni(II). Moreover, ab initio CASSCF/RASSI-SO with the OpenMolcas unambiguously reveals large positive zero-field split (ZFS) parameters D value (87.4 cm–1) and gx,y > gz, which exhibit easy-plane anisotropy for 1. Conversely, complex 2 is characterized as isolated easy-axis anisotropy, evidenced by their negative D value (−25.5 cm–1) and gz > gx,y, showing ferromagnetic (FM) coupling. Overall, this work offers a kind of thinking of designing isostructural CPs with different magnetic properties.