Ferric oxalate, also known as iron(III) oxalate, is a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one elemen ...

composed of

ferric In chemistry, iron(III) refers to the element iron in its +3 oxidation state. In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe3+. The adjective ferric or the prefix ferri- is often used to sp ...

ions and

oxalate Oxalate (IUPAC: ethanedioate) is an anion with the formula C2O42−. This dianion is colorless. It occurs naturally, including in some foods. It forms a variety of salts, for example sodium oxalate (Na2C2O4), and several esters such as dimethyl o ...

ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electro ...

s; it may also be regarded as the ferric salt of

oxalic acid Oxalic acid is an organic acid with the systematic name ethanedioic acid and formula . It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name comes from the fact that early investi ...

. The anhydrous material is pale yellow; however, it may be hydrated to form several

hydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was underst ...

s, such as

potassium ferrioxalate Potassium ferrioxalate, also called potassium trisoxalatoferrate or potassium tris(oxalato)ferrate(III) is a chemical compound with the formula []. It often occurs as the trihydrate . Both are crystalline compounds, lime green in colour.A. Sarith ...

, or , which is bright green in colour.

Structure

Tetrahydrate

The crystal structure of the tetrahydrate was determined in 2015. It has a triclinic unit cell containing two iron atoms. Each iron atom has octahedral coordination bonds to the oxygen atoms of three oxalate molecules and one water molecule. Two of those three oxalates, lying in approximately perpendicular planes, are tetradentate, and connect the iron atoms into zigzag chains. The third oxalate molecule is bidentate, and connects iron atoms of adjacent chains, creating an open-layered structure. Half of the water molecules lie, unbound, between those chains. Mössbauer spectrum of indicates that iron is present in a unique environment with an isomer shift of 0.38 mm/s and a quadrupole splitting of 0.40 mm/s, suggesting a high spin in octahedral coordination.

Uses

Dentistry

Like many oxalates, ferric oxalate has been investigated as a short-term treatment for

dentin hypersensitivity Dentin hypersensitivity (DH, DHS) is dental pain which is sharp in character and of short duration, arising from exposed dentin surfaces in response to stimuli, typically thermal, evaporative, tactile, osmotic, chemical or electrical; and which ca ...

. It is used in certain toothpaste formulations; however, its effectiveness has been questioned.

Photography

Ferric oxalate is used as the light-sensitive element in the

Kallitype Kallitype is a process for making photographic prints. Patented in 1889 by W. W. J. Nicol (1855-1929), the Kallitype print is an iron-silver process. A chemical process similar to the Van Dyke brown based on the use of a combination of ferric and ...

photographic printing process; and the platinotype process Platinum/Palladium Printing.

Batteries

Ferric oxalate tetrahydrate has been investigated as a possible cheap material for the positive electrode of lithium-iron batteries. It can intercalate

lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid e ...

ions at an average potential of 3.35 V, and has shown a sustainable capacity of 98 mAh/g.

Organic synthesis

Ferric oxalate hexahydrate is used with

sodium borohydride Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound with the formula Na BH4. This white solid, usually encountered as an aqueous basic solution, is a reducing agent that finds applica ...

for radical

Markovnikov Markovnikov (russian: Марковников) is a Russian masculine surname, which originates from ''морковь'' (''carrot''); its feminine counterpart is Markovnikova. It may refer to *Vladimir Markovnikov (1837–1904), Russian chemist * Nik ...

hydrofunctionalization A hydrofunctionalization reaction is the addition of hydrogen and another univalent fragment (X) across a carbon-carbon or carbon-heteroatom multiple bond. Often, the term ''hydrofunctionalization'' without modifier refers specifically to the use o ...

reactions of alkenes.

References

{{Oxalates [ ategory:Iron(III) compounds Oxalates Inorganic compounds