Ferric EDTA#Synthesis and structure

Solutions of Fe(III)-EDTA are produced by combining ferrous salts and aqueous solutions of EDTA and aerating them:{{cite journal|author=Jacobson, L.|title=Maintenance of Iron Supply in Nutrient Solutions by a Single Addition of Ferric Potassium Ethylenediamine Tetra-Acetate|journal=Plant Physiology|year=1951|volume=26|issue=2|pages=411–413|pmc=437509|doi=10.1104/pp.26.2.411|pmid=16654380}}

:FeSO₄∙7H₂O + K₂H₂Y + 1/4 O₂ → K[FeY(H₂O)]^.H₂O + KHSO₄ + 5.5 H₂O

Near neutral pH, the principal complex is [Fe(EDTA)(H₂O)]⁻, although most sources ignore the aquo ligand. The tetraanion EDTA⁴⁻ wraps around the metal ion, binding through four carboxylates and two amines. The [Fe(EDTA)(H₂O)]⁻ anion has been crystallized with many cations, e.g., the trihydrate Na[Fe(EDTA)(H₂O)]^.2H₂O.{{cite journal|author1=Solans, X.|author2=Font Altaba, M.|author3=Garcia-Oricain, J.|title=Crystal Structures of Ethylenediaminetetraacetato Metal Complexes. V. Structures Containing the [Fe(C₁₀H₁₂N₂O₈)(H₂O)]⁻ Anion|journal=Acta Crystallographica Section C|year=1984|volume=40|issue=4|pages=635–638|doi=10.1107/S0108270184005151}} The salts as well as the solutions are yellow-brown. Provided the standard nutrient solution in which the [Fe(EDTA)(H₂O)]⁻ complex will be used has a pH of at least 5.5, all the uncomplexed iron, as a result of incomplete synthesis reaction, will still change into the chelated ferric form.{{cite journal|author1=Steiner, A.A.|author2=van Winden, H.|title=Recipe for Ferric Salts of Ethylenediaminetetraacetic Acid|journal=Plant Physiology|year=1970|volume=46|issue=6|pages=862–863|pmc=396702|doi=10.1104/pp.46.6.862|pmid=16657561}}

EDTA is used to solubilize iron(III) in water. In the absence of EDTA or similar chelating agents, ferric ions form insoluble solids and are thus not bioavailable.

Together with pentetic acid (DTPA), EDTA is widely used for sequestering metal ions. Otherwise these metal ions catalyze the decomposition of hydrogen peroxide, which is used to bleach pulp in papermaking. Several million kilograms EDTA are produced for this purpose annually.J. Roger Hart "Ethylenediaminetetraacetic Acid and Related Chelating Agents" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005.{{doi|10.1002/14356007.a10_095}}

Iron chelate is commonly used for agricultural purposes to treat chlorosis, a condition in which leaves produce insufficient chlorophyll. Iron and ligand are absorbed separately by the plant roots whereby the highly stable ferric chelate is first reduced to the less stable ferrous chelate.{{cite journal|author=Van Driel, W.|title=The effect of iron ethylenediaminetetraacetic acid on the growth and metabolism of tomato plants in water culture|journal=Plant and Soil|year=1964|volume=20|pages=85–104|doi=10.1007/BF01378101|s2cid=28252630 }} In horticulture, iron chelate is often referred to as 'sequestered iron' and is used as a plant tonic, often mixed with other nutrients and plant foods (e.g., seaweed). It is recommended in ornamental horticulture for feeding ericaceous plants like Rhododendrons if they are growing in calcareous soils. The sequestered iron is available to the ericaceous plants, without adjusting the soil's pH, and thus, lime-induced chlorosis is prevented.

Ferric EDTA can be used, for example, as an essential component of the Hoagland solution or the Long Ashton Nutrient Solution.Hewitt E. J. (1966). Sand and Water Culture Methods Used in the Study of Plant Nutrition. Farnham Royal, England: Commonwealth Agricultural Bureaux, pp. 547. Technical Communication No. 22 (Revised 2nd Edition) of the Commonwealth Bureau of Horticulture and Plantation Crops. According to Jacobson (1951), the stability of ferric EDTA was tested by adding 5 ppm iron, as the complex, to Hoagland's solution at various pH values. No loss of iron occurred below pH 6. In addition to Jacobson's original recipe and a modified protocol by Steiner and van Winden (1970), an updated version for producing the ferric EDTA complex is available by Nagel et al. (2020).{{cite journal|author1=Nagel, K.A.|author2=Lenz, H.|author3=Kastenholz, B.|author4=Gilmer, F.|author5=Averesch, A.|author6=Putz, A.|author7=Heinz, K.|author8=Fischbach, A.|author9=Scharr, H.|author10=Fiorani, F.|author11=Walter, A.|author12=Schurr, U.|title=The platform GrowScreen-Agar enables identification of phenotypic diversity in root and shoot growth traits of agar grown plants |journal=Plant Methods |volume=16 |issue=89 |pages=1–17|doi=10.1186/s13007-020-00631-3|pmc=7310412|year=2020|pmid=32582364 |doi-access=free}}

Iron chelate has also been used as a bait in the chemical control of slugs, snails and slaters in agriculture in Australia and New Zealand. They have advantages over other more generally poisonous substances used as their toxicity is more specific to molluscs.{{cite web|url=http://www.regional.org.au/au/asa/2001/6/c/young.htm|title=Slugs, Snails and Iron based Baits: An Increasing Problem and a Low Toxic Specific Action Solution|last=Young CL, Armstrong GD|year=2001|work=Australian Society of Agronomy|publisher=The Regional Institute |access-date=2009-10-18}}

Ferric EDTA is used as a photographic bleach to convert silver metal into silver salts, that can later be removed.

{{main|Aminopolycarboxylic acid}}

Aside from EDTA, the chelating agents EDDHA and pentetic acid (DTPA), used to solubilize iron in water. It also can be used for the purposes of agriculture as it is bioavailable to plants.{{cite journal|author1=Batra, P.P.|author2=Maier, R.H.|title=Isolation and determination of the ferric iron chelate of ethylenediamine di(o-hydroxyphenylacetic acid) in plant tissues|journal=Plant and Soil|year=1964|volume=20|pages=105–115|doi=10.1007/BF01378102|s2cid=9873911 }}

In iron chelation therapy, deferoxamine, has been used to treat excess iron stores, i.e. haemochromatosis.{{cite web|url=https://www.cdc.gov/ncbddd/hemochromatosis/training/treatment/monitoring_treatment.htm |title=Hemochromatosis: Monitoring and Treatment |access-date=2009-10-18 |date=2007-11-01 |publisher=National Center on Birth Defects and Developmental Disabilities (NCBDDD) |url-status=dead |archive-url=https://web.archive.org/web/20090518203600/http://www.cdc.gov/ncbddd/hemochromatosis/training/treatment/monitoring_treatment.htm |archive-date=May 18, 2009 }}

• DTPA
• EDDHA
• Tartrate
• Citrate

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Category:Iron(III) compounds

Category:Coordination complexes