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

The molecular structures for thermal activated and photoinduced electr onic spin state of [Fe(pic)(3)]Cl-2 . EtOH (pic = alpha-picolylamine) in ethanol solution are studied using EXAFS and optical absorption spe ctroscopies. Structural studies of the thermally activated spin state in this compound were also conducted on the crystalline solid. The exp erimental 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 s olid for the thermally activated spin state where the Fe-N bond distan ces 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 me tastable intermediate with a structure different from either the high spin or the low spin state. The analysis of the experimental data indi cates that the Fe-N bond distances in this intermediate are divided in to 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 distorti on of the octahedral structure probably due to electron transfer betwe en the solvent and the solute molecules or to an intermediate state wi th tripler character stabilized by a pseudo D-4h field.