A Dicobalt(II) Single-Molecule Magnet via a Well-Designed Dual-Capping Tetrazine Radical Ligand

Abstract

The recent years have witnessed the glory development for the construction of high-performance mononuclear single molecule magnets (SMMs) within a specific coordination geometry, which, however, is not well applied in cluster-based SMMs due to the synthetic challenges. Given that the monocobalt-(II) complexes within a trigonal-prismatic (TPR) coordination geometry have been classified as excellent SMMs with huge axial anisotropy (D ≈ −100 cm −1 ), here we designed and synthesized a new dual-capping tetrazine ligand, 3,6-bis(6-(di(1Hpyrazol-1-yl)methyl)pyridin-2-yl)-1,2,4,5-tetrazine (bpptz), and prepared a novelIn the structure of 1, the bpptz •− radical ligand enwraps two Co(II) centers within quasi-TPR geometries, which are further bridged by the tetrazine radical in the trans mode. The magnetic study revealed that the interaction between the Co centers and the tetrazine radical is strongly antiferromagnetic with a coupling constant (J) of −65.8 cm −1 (in the −2J formalism). Remarkably, 1 exhibited the typical SMM behavior with an effective energy barrier of 69 cm −1 under a 1.5 kOe dc field, among the largest for polynuclear transition metal SMMs. In addition, DFT and ab initio calculations suggested that the presence of a strong Co(II)−radical magnetic interaction effectively quenches the QTM effect and enhances the barrier height for the magnetization reversal.

Three isostructural MOFs based on different metal cations: proton conductivities and SC–SC transformation leading to magnetic changes

“…[58][59][60] The unsaturated and non-superimposed curves suggest the presence of significant magnetic anisotropy in these two compounds. [61][62][63][64] Obviously, the M versus H/kOe curve of 1 at 2.0 K shows a clear inflection at around 1.5 kOe, and reaches a maximum value of 4.69μ B at about 70 kOe. By comparison, the rapidly rising M curve can be detected in 1•CH 3 OH.…”

Spirobifluorene Mediating the Spin–Spin Coupling of Nitronyl Nitroxide Diradicals

“…Therefore, it is widely used as a spin carrier in the design of molecular magnetic materials, 1,11,12 with the expected AF or ferromagnetic (FM) spin-exchange interaction. 13,14 In previous works, the primary strategy was to obtain higher spin organic magnetic materials based on molecular topology, 15,16 like π-conjugated rigid molecules, 17−19 metal ion coordination molecules, 20,21 and self-assembled molecules. 22−24 Since 1967, when Simmons and Fukunaga first proposed spiro conjugation, it has been confirmed by theoretical and experimental chemistry in many cases.…”

“…Nitronyl nitroxides are thermodynamically stable due to their electron-delocalized structure. Therefore, it is widely used as a spin carrier in the design of molecular magnetic materials, ,, with the expected AF or ferromagnetic (FM) spin-exchange interaction. , In previous works, the primary strategy was to obtain higher spin organic magnetic materials based on molecular topology, , like π-conjugated rigid molecules, − metal ion coordination molecules, , and self-assembled molecules. − …”

Synthesis, structure, magnetic properties of one‐dimensional Cu‐Ln chains linked by a nitronyl nitroxide radical with two pyridyl groups

“…It is, however, still a great challenge to improve the magnetic behaviors of 4f-3d based SMMs. Recently, an appealing strategy is to use paramagnetic radical ligands for constructing 4f-3d based complexes, i. e. 2p-3d-4f system, [29][30][31][32][33][34][35][36][37][38] in which three kinds of different spins may work in a synergistic way resulting in interesting magnetic behavior. Andruh et al have reported a 2p-3d-4f SMM [Co II Dy III Rad] involving the end-off bicompartmental ligand combined with a nitronyl nitroxide unit.…”