Ferric acetate is the acetate salt of the
coordination complex [Fe3O(OAc)6(H2O)3+ (OAc− is CH3CO2−). Commonly the salt is known as "basic iron acetate".[3] The formation of the red-brown complex was once used as a test for
ferric ions.[4]
Structure and synthesis
Basic iron acetate forms on treating aqueous solutions of iron(III) sources with acetate salts.[5] A typical precursor is freshly precipitated iron oxide/hydroxide, which is halide-free.[6]
Early work showed that the cation is trinuclear.[7] The Fe centres are equivalent, each being
octahedral, being bound to six oxygen ligands, including a triply bridging oxide at the center of the equilateral triangle.[8] The compound was an early example of a molecular complex of iron that features an oxide ligand. The cation has idealized D3hsymmetry.
Reactions
The terminal aqua ligands on the trimetallic framework can be substituted with other ligands, such as
pyridine and
dimethylformamide. Many different salts are known by exchanging the anion, e.g. [Fe3(μ3-O)(OAc)6(H2O)3]Cl. Reduction of the cation affords the neutral mixed-valence derivative that contains one ferrous and two ferric centers.[3] Mixed metal species are known such as [Fe2CoO(OAc)6(H2O)3].[9]
Related compounds
Chromium(III), ruthenium(III), vanadium(III), manganese(III) and rhodium(III) form analogous compounds.[10] Iron(III) acetate (lacking the oxo ligand) has been claimed as a red coloured compound from the reaction of
silver acetate and
iron(III) chloride.[11]
Uses
Materials prepared by heating iron, acetic acid, and air, loosely described as basic iron acetates, are used as
dyes and
mordants.[3]
Iron acetate is often brushed upon untreated wood to give it an aged appearance.
^Figgis, B. N.; Robertson, G. B. (13 February 1965). "Crystal-Molecular Structure and Magnetic Properties of Cr3(CH3.COO)6OCl.5H2O". Nature. 205 (4972): 694–695.
Bibcode:
1965Natur.205..694F.
doi:
10.1038/205694a0.
S2CID4283321. This paper describes the isostructure chromium and iron compounds.
^Blake, Antony B.; Yavari, Ahmad; Hatfield, William E.; Sethulekshmi, C. N. (1985). "Magnetic and spectroscopic properties of some heterotrinuclear basic acetates of chromium(III), iron(III), and divalent metal ions". Journal of the Chemical Society, Dalton Transactions (12): 2509.
doi:
10.1039/DT9850002509.
^Holleman, Arnold Frederik; Wiberg, Egon (2001), Wiberg, Nils (ed.), Inorganic Chemistry, translated by Eagleson, Mary; Brewer, William, San Diego/Berlin: Academic Press/De Gruyter,
ISBN0-12-352651-5