Synthesis, crystal structures and properties of the novel mononuclear copper(II) and tetranuclear cobalt(II) complexes with 3,6-bis-(3,5-dimethylpyrazolyl)-pyridazine

Strong Coupling and Slow Relaxation of the Magnetization for an Air-Stable [Co4] Square with Both Tetrazine Radicals and Azido Bridges

Introducing both tetrazine radical and azido bridges afforded two air-stable square complexes [M^II₄(bpztz^•-)₄(N₃)₄] (M^II = Zn²⁺, 1; Co²⁺, 2; bpztz = 3,6-bis(3,5-dimethylpyrazolyl)-1,2,4,5-tetrazine), where the metal ions are cobridged by μ_1,1-azido bridges and tetrazine radicals. Magnetic studies revealed strong antiferromagnetic metal-radical interaction with a coupling constant of -64.7 cm^-1 in the 2J formalism in 2. Remarkably, 2 exhibits slow relaxation of magnetization with an effective barrier for spin reverse of 96 K at zero applied field.

Heteroleptic ruthenium(II) 2,2′-bipyridine complexes incorporating substituted pyrazol-1-yl-pyridazine ancillaries

Condensation of 3,6-dichloropyridazine or 3,6-dichloro-4,5-dimethyl- pyridazine with 3-methyl-1H-pyrazole or 4-methyl-1H-pyrazole with the assistance of sodium metal in tetrahydrofuran at reflux afforded three 3,6-bis(pyrazolyl)- pyridazine-type ligands: 3,6-bis(3-methylpyrazolyl)pyridazine (L1), 3,6-bis(4-methyl- pyrazolyl)pyridazine (L2) and 4,5-dimethyl-3,6-bis(4-methylpyrazolyl)pyridazine (L3). Reactions of cis-[RuCl2(bpy)2] · 2H2O (bpy = 2,2′-bipyridine) and L1, L2 or L3 in the presence of NH4PF6 produced the heteroleptic cationic ruthenium(II) complexes [Ru(L1)(bpy)2](PF6)2 (1), [Ru(L2)(bpy)2](PF6)2 (2) and [Ru(L3)(bpy)2](PF6)2 (3), respectively. The three complexes have been characterized by UV/Vis and luminescence spectroscopy. The crystal structures of 1 · EtOH, 2 · EtOH and 3 have been determined by single-crystal X-ray diffraction.

Two azido-bridged [2×2] cobalt(ii) grids featuring single-molecule magnet behaviour

Two Co(ii) [2 × 2] grid-like clusters containing both pyridazine and azido bridges were reported to exhibit overall intramolecular ferromagnetic coupling and field-induced single-molecule magnet behavior with the effective energy barriers up to 56 K.