Formation of acetylacetonato iron complexes in acetonitrile and their resonance Raman spectra

Abstract

Formation of acetylacetonato from complexes in acetonitrile, Fe(acac) 2+, Fe(acac) 2 + and Fe(acac) 3, (the expression represents the solvated species: acac - is the 2, 4-pentanedionate ion), were spectrophotometrically studied. On addition of Hacac to an acetonitrile solution of Fe(ClO 4) 3, Fe(acac) 2+ was quantitatively formed. When excess Hacac was added, only Fe(acac) 2 + was obtained without forming Fe(acac) 3. On the other hand, Fe(acac) 2 + was quantitatively obtained by adding HClO 4 to an acetonitrile solution of Fe(acac) 3, and Fe(acac) 2+ was also formed by adding an excess of HClO 4. All the species of acetylacetonato complexes: Fe(acac) 2+, Fe(acac) 2 + and Fe(acac) 3 were formed in the system of Fe(ClO 4) 3 with an addition of tetraethylammonium acetylacetonate. The resonance Raman spectra of the obtained solutions of Fe(acac) 2+ and Fe(acac) 2 + and of the solution of Fe(acac) 3 were measured. The peaks mainly associated with v(FeO) and v(CO) are observed near 450 and 1600 cm -1, respectively. The order of v(FeO) is Fe(acac) 2+ (474 cm -1) > Fe(acac) 2 + (462 cm -1) > Fe(acac) 3 (451 cm -1) and that of v(CO) is Fe(acac) 2+ (1554 cm -1) < Fe(acac) 2 + (1578 cm -1) < Fe(acac) 3 (1603 cm -1). These results indicate that the coordination strength of acac - to Fe becomes weaker, because the Lewis acidity of the metal decreases as the number of coordinated acac - increases.