Synthesis, structures, and magnetic properties of crystals of dinuclear copper(II) and cobalt(II) complexes with 3-(3,5-dimethylpyrazol-1-yl)-6-R-1,2,4,5-tetrazines

摘要

Dinuclear complexes of Cu~(II) with 3-(3,5-dimethylpyrazol-1-yl)-6-(2-hydroxyethylami-no)-1,2,4,5-tetrazine (1) and Co~(II) with 3-(3,5-dimethylpyrazol-1-yl)-6-(piperidin-1-yl)-1,2,4,5- tetrazine (2) were synthesized and structurally characterized, and the magnetic (SQUID) and resonance (EPR) properties of van der Waals crystals based on these complexes were studied. Unusual behavior of the effective magnetic moment μ_(eff) (T) is observed at T< 60 K. A nonmonotonic increase in μ_(eff) (T) for 1 (~6 %) and a 20% reduction of μ_(eff) (T) for 2 have a common origin and are due to the influence of spin-orbital coupling on the character of the splitting between the t_(2g) and e_g levels of the central ion. Distortions of the coordination site "switch on" a positive (1) or negative (2) contribution of the orbital magnetic moment near 6 K. Irreversible temperature behavior of μ_(eff) (T) in the heating and cooling regimes in the vicinity of 60 K suggests that the character of structural distortions and the magnetic properties are related to ligand geometry. This factor plays a significant role in crystal engineering of magnetoactive structures with polynitrogen ligands.