X-RAY-ABSORPTION STUDIES ON ELECTRONIC SPIN-STATE TRANSITIONS OF FE(II) COMPLEXES IN DIFFERENT MEDIA

The molecular structures for thermal activated and photoinduced electronic spin state of [Fe(pic)(3)]Cl-2 . EtOH (pic = alpha-picolylamine) in ethanol solution are studied using EXAFS and optical absorption spectroscopies. Structural studies of the thermally activated spin state in this compound were also conducted on the crystalline solid. The experimental results show that the Fe-N bond length change in [Fe(pic)(3)]Cl-2 . EtOH solution is similar to that observed in the crystalline solid for the thermally activated spin state where the Fe-N bond distances are 2.00 +/- 0.02 and 2.20 +/- 0.02 Angstrom for the low spin and the high spin states respectively. However, photoexcitation of the low spin state [Fe(pic)(3)]Cl-2 . EtOH in solution at 10 K generated a metastable intermediate with a structure different from either the high spin or the low spin state. The analysis of the experimental data indicates that the Fe-N bond distances in this intermediate are divided into two sets with average bond distances of 1.94 +/- 0.04 and 2.11 +/- 0.04 Angstrom. This phenomenon is attributed to a Jahn-Teller distortion of the octahedral structure probably due to electron transfer between the solvent and the solute molecules or to an intermediate state with tripler character stabilized by a pseudo D-4h field.