In: Chemistry
The molecular structures of Cr(acac)3 and Fe(acac)3 are quite different from that of Mn(acac)3. What are these structures? What is the true structure of the so-called manganic acetate? Please explain thoroughly.
Metal acetylacetonates are coordination
complexes derived from the acetylacetonate anion (CH
3COCHCOCH−3) and metal ions, usually transition metals. The
bidentate ligand acetylacetonate is often abbreviated acac.
Typically both oxygen atoms bind to the metal to form a
six-membered chelate ring.
Chromium(III) acetylacetonate, Cr(acac)3, with the formula Cr(C5H7O2)3, is a typical octahedral complex containing three acac− ligands. Like most such compounds, it is highly soluble in nonpolar organic solvents. This particular complex, which has a three unpaired electrons, is used as a spin relaxation agent to improve the sensitivity in quantitative carbon-13 NMR spectroscopy. The compound is prepared by the reaction of chromium(III) oxide with acetylacetone (Hacac):
Cr2O3 + 6 Hacac → 2 Cr(acac)3 + 3 H2O
Iron(III) acetylacetonate, Fe(acac)3, is a red high-spin complex that is highly soluble in organic solvents. It is a configurationally labile, high-spin complex with five unpaired electrons. It is occasionally used as a catalyst precursor. Fe(acac)3 is prepared by treating freshly precipitated Fe(OH)3 with acetylacetone.
Fe(OH)3 + 3 HC5H7O2 → Fe(C5H7O2)3 + 3 H2O
manganese(II) acetylacetonate, Mn(acac)2, has been prepared by the comproportionation of the manganese(II) compound Mn(acac)2 with potassium permanganate in the presence of additional acetylacetone.
The true Structure of Mn(acac)3 is in the Image...................................