The effect of ammine,ethanoate, trichloro- and trifluoroethanoate ligands on tris(2,4-pentanedionato) chromium(III) formation in high pH aqueous solution

The yields of tris(2,4-pentanedionato)chrvmium(III) (Cr(acac)₃) formed in the presence of either the ammonia (Am), ethanoate (ET), trichloroethanoate (TCE), or trifluoroethanoate (TFE) ligand in high pH aqueous solution, were compared with those from a medium containing only hydroxyl and water as the principal ligands besides the acac. The presence of Am, ET, and TCE drastically reduced the yields at pH’s 9.5–10.5, 7.5–9.0/9.5–11.0, and 9.0–12.0, respectively in increasing order ET > Am < TCE. The role of Am is attributed mainly to the oxo-bridged species ((OH)_m(H₂O)_nAm_5-(m+n)Cr(O)(OH)CrAm_5-(m+n)(H₂O)_n(OH)_m)^3-2m (1), ((OH)_m(H₂O)_nAm_5-(m+n)Cr(O)₂CrAm_5-(m+n)(H₂O)_n(OH)_m)^2-2m (2), and ((OH)_m(H₂O)_nAm_5-(m+n)Cr(O)(OH)CrAm_4(m+n)(H₂O)_n(OH)_m+1)^2-2m (3). 2 is the most deactivating species mainly on the basis that the Cr-O bond of the oxo-bridge is suggested as being stronger than the Cr-O bond of the hydroxo-bridge. As for ET and TCE, oxo-bridged polymeric ethanoato- and trichloroethanoatochromium(III) species are also proposed as the main origin of the drastic deactivation of the reaction not observed for TFE due possibly, to the insignificance of oxo-bridges in tnfluoroethanoatochromium(III) species.