Theoretical calculations using density functional methods have been performed on two dinuclear {Ni^II–Gd^III} and two trinuclear {Ni^II–Gd^III–Ni^II} complexes having two and three μ-OR (R = alkyl or aromatic groups) bridging groups. The different magnetic behaviour, having moderately strong ferromagnetic coupling for complexes having two μ-OR groups and weak ferromagnetic coupling for complexes having three μ-OR groups, observed experimentally is very well reproduced by the calculations. Additionally, computation of overlap integrals MO and NBO analysis reveals a clear increase in antiferromagnetic contribution to the net exchange for three μ-OR bridged {Ni–Gd} dimers and also provides several important clues regarding the mechanism of magnetic coupling. Besides, MO and NBO analysis discloses the role of the empty 5d orbitals of the Gd^III ion on the mechanism of magnetic coupling. Magneto-structural correlations for Ni–O–Gd bond angles, Ni–O and Gd–O bond distances, and the Ni–O–Gd–O dihedral angle have been developed and compared with the published experimental {Ni–Gd} structures and their J values indicate that the Ni–O–Gd bond angles play a prominent role in these types of complexes. The computation has then been extended to two trinuclear {Ni^II–Gd^III–Ni^II} complexes and here both the {Ni–Gd} and the {Ni–Ni} interactions have been computed. Our calculations reveal that, for both structures studied, the two {NiGd} interactions are ferromagnetic and are similar in strength. The {Ni–Ni} interaction is antiferromagnetic in nature and our study reveals that its inclusion in fitting the magnetic data is necessary to obtain a reliable set of spin Hamiltonian parameters. Extensive magneto-structural correlations have been developed for the trinuclear complexes and the observed J trend for the trinuclear complex is similar to that of the dinuclear {Ni–Gd} complex. In addition to the structural parameters discussed above, for trinuclear complexes the twist angle between the two Ni–O–Gd planes is also an important parameter which influences the J values.

We report the design and synthesis of a 1D Dy(III) coordination polymer, comprised of sulfonate functionalised ligand 8-hydroxyquinoline-5-sulfonic acid (H₂SQ) and Dy³⁺ ions, with a hydrogen-bonded supramolecular 3D structure. Interestingly, the coordination compound can exhibit reversible structural transformation from a trihydrate (1·3H₂O) to a monohydrate (1·H₂O) phase during partial desorption/adsorption processes of water molecules in a single-crystal-to-single-crystal (SC–SC) fashion. Importantly, the field-induced slow magnetic relaxation behaviour and proton conduction performance were both switched during the dynamic structural transformation, giving rise to a proton conductive SIM of 1·3H₂O and a SIM-insulator of 1·H₂O. Variable temperature single-crystal structural analyses reveal that the non-coordinated water molecules play a vital role in the changes in primary coordination environments around the Dy³⁺ ions, and the global hydrogen-bonding networks, resulting in the modification of magnetic properties and proton transport pathways in 1·3H₂O and 1·H₂O, respectively. The previous results not only provide the first example of a Dy(III) sulfonate showing switched single-ion magnetism and proton conduction behaviour but also highlight a promising way to use water for dynamic control of magnetic and electrical properties.

Herein we report the tunable structures, magnetic interactions, magnetic anisotropy, and SMM behavior via selective pyridine derivatives in two Co(ii) coordination polymers.