Field-induced single ion magnet behaviour of discrete and one-dimensional complexes containing [bis(1-methylimidazol-2-yl)ketone]-cobalt(II) building units

The crystal structure of diaqua-bis(pyrazolo[1,5-a]pyrimidine-3-carboxylato-κ2 N,O)-cobalt(II) dihydrate, C14H16N6O8Co

C14H16N6O8Co, monoclinic, P21/n (no. 14), a = 6.3520 (6) Å, b = 11.7438 (8) Å, c = 11.7880 (9) Å, β = 96.562 (9)°, V = 873.58 (12) Å3, Z = 2, R gt(F) = 0.0508, wR ref(F 2) = 0.0982, T = 290 K.

A porous cobalt(II)-organic framework exhibiting high room temperature proton conductivity and field-induced slow magnetic relaxation

A two-dimensional (2D) cobalt(II) metal-organic framework (MOF) constructed by a ditopic organic ligand, formulated as {[Co(Hbic)(H₂O)]·4H₂O}_n (1) (H₂bic = 1H-benzimidazole-5-carboxylic acid), was hydrothermally synthesized and structurally characterized. Single-crystal X-ray diffraction shows that the distorted octahedral Co²⁺ ions, as coordination nodes, are bridged to form 2D honeycomb networks, which are further organized into a 3D supramolecular porous framework through multiple hydrogen bonds and interlayer π-π interactions. Dynamic crystallography experiments reveal the anisotropic thermal expansion behavior of the lattice, suggesting a flexible hydrogen-bonded 3D framework. Interestingly, hydrogen-bonded (H₂O)₄ tetramers were found to be located in porous channels, yielding 1D proton transport pathways. As a result, the compound exhibited a high room-temperature proton conductivity of 1.6 × 10^-4 S cm^-1 under a relative humidity of 95% through a Grotthuss mechanism. Magnetic investigations combined with theoretical calculations reveal giant easy-plane magnetic anisotropy of the distorted octahedral Co²⁺ ions with the experimental and computed D values being 87.1 and 109.3 cm^-1, respectively. In addition, the compound exhibits field-induced slow magnetic relaxation behavior at low temperatures with an effective energy barrier of U_eff = 45.2 cm^-1. Thus, the observed electrical and magnetic properties indicate a rare proton conducting SIM-MOF. The foregoing results provide a unique bifunctional cobalt(II) framework material and suggest a promising way to achieve magnetic and electrical properties using a supramolecular framework platform.

The Role of the Bridge in Single-Ion Magnet Behaviour: Reinvestigation of Cobalt(II) Succinate and Fumarate Coordination Polymers with Nicotinamide

Two previously synthesized cobalt(II) coordination polymers; {[Co(μ2-suc)(nia)2(H2O)2]·2H2O}n (suc = succinate(2−), nia = nicotinamide) and [Co(μ2-fum)(nia)2(H2O)2]n (fum = fumarate(2−)) were prepared and thoroughly characterized. Both complexes form 1D coordination chains by bonding of Co(nia)2(H2O)2 units through succinate or fumarate ligands while these chains are further linked through hydrogen bonds to 3D supramolecular networks. The intermolecular interactions of both complexes are quantified using Hirshfeld surface analysis and their infrared spectra, electronic spectra and static magnetic properties are confronted with DFT and state-of-the-art ab-initio calculations. Dynamic magnetic measurements show that both complexes exhibit single-ion magnet behaviour induced by a magnetic field. Since they possess very similar chemical structure, differing only in the rigidity of the bridge between the magnetic centres, this chemical feature is put into context with changes in their magnetic relaxation.