A photomagnetic study of three iron(II) compounds containing ligands from the 2,6-di(pyrazol-1-yl)pyridine series

A comprehensive study of the photomagnetic behaviour of [Fe(L1)2](BF4)2, [Fe(L2)2](BF4)2 and [Fe(L2)2](ClO4)2 where L1=2,6-di(pyrazol-1-yl)pyridine and L2=2,6-di(pyrazol-1-yl)pyrazine has been carried out. The critical Light Induced Excited Spin State Trapping (LIESST) temperatures (T(LIESST)) of all three compounds are presented. The kinetics of the transition from the metastable high spin state to the low spin state have been investigated and examination of the photomagnetic behaviour under constant irradiation has shown the Light Induced Thermal Hysteresis (LITH) behaviour of the compounds. This work completes the crystallographic data previously published and proves the quantitative photoconversion at low temperature of all these derivatives.