Technetium(IV) oxide, also known as technetium dioxide, is a chemical compound with the formula TcO₂ which forms the dihydrate, TcO₂·2H₂O, which is also known as technetium(IV) hydroxide. It is a radioactive black solid which slowly oxidizes in air.

Preparation

Technetium dioxide was first produced in 1949 by electrolyzing a solution of

ammonium pertechnetate Ammonium pertechnetate is a chemical compound with the formula NH4TcO4. It is the ammonium salt of pertechnetic acid. The most common form uses 99Tc. The compound is readily soluble in aqueous solutions forming ammonium and pertechnetate ions. ...

under

ammonium hydroxide Ammonia solution, also known as ammonia water, ammonium hydroxide, ammoniacal liquor, ammonia liquor, aqua ammonia, aqueous ammonia, or (inaccurately) ammonia, is a solution of ammonia in water. It can be denoted by the symbols NH3(aq). Although ...

and this method is used for separating technetium from

molybdenum Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lea ...

and

rhenium Rhenium is a chemical element with the symbol Re and atomic number 75. It is a silvery-gray, heavy, third-row transition metal in group 7 of the periodic table. With an estimated average concentration of 1 part per billion (ppb), rhenium is one ...

. There are now more efficient ways of producing the compound, such as the reduction of ammonium pertechnetate by

zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...

metal and

hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid Acid strength is the tendency of an acid, symbol ...

stannous chloride Tin(II) chloride, also known as stannous chloride, is a white crystalline solid with the formula . It forms a stable dihydrate, but aqueous solutions tend to undergo hydrolysis, particularly if hot. SnCl2 is widely used as a reducing agent (in acid ...

hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...

hydroxylamine Hydroxylamine is an inorganic compound with the formula . The material is a white crystalline, hygroscopic compound.Greenwood and Earnshaw. ''Chemistry of the Elements.'' 2nd Edition. Reed Educational and Professional Publishing Ltd. pp. 431–43 ...

ascorbic acid Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) an ...

, by the hydrolysis of potassium hexachlorotechnate or by the decomposition of ammonium pertechnetate at 700 °C under an inert atmosphere: :2 NH₄TcO₄ → 2 TcO₂ + 4 H₂O + N₂ All of these methods except the last lead to the formation of the dihydrate. The most modern method of producing this compound is by the reaction of ammonium pertechnetate with

sodium dithionite Sodium dithionite (also known as sodium hydrosulfite) is a white crystalline powder with a sulfurous odor. Although it is stable in dry air, it decomposes in hot water and in acid solutions. Structure The structure has been examined by Raman s ...

Properties

The dihydrate dehydrates to anhydrous technetium dioxide at 300 °C, and if further heated sublime at 1100 °C under an inert atmosphere, however, if oxygen is present, it will react with the oxygen to produce

technetium(VII) oxide Technetium(VII) oxide is the chemical compound with the formula Tc2O7. This yellow volatile solid is a rare example of a molecular binary metal oxide, the other examples being RuO4, OsO4, and the unstable Mn2O7. It adopts a centrosymmetric c ...

at 450 °C. If water is present,

pertechnetic acid Pertechnetic acid (HTcO4) is a compound of technetium that is produced by reacting technetium(VII) oxide (Tc2O7) with water or strong oxidizing acids, such as nitric acid, concentrated sulfuric acid or aqua regia. The dark red hygroscopic sub ...

is produced by the reaction of technetium(VII) oxide with water. If technetium dioxide is treated with a base, such as

sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and alkali ...

, it forms the hydroxotechnetate(IV) ion, which is easily oxidized to

in numerous ways, such as the reaction with alkaline

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%� ...

, concentrated

nitric acid Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...

bromine Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table (halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simila ...

, or tetravalent

cerium Cerium is a chemical element with the symbol Ce and atomic number 58. Cerium is a soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it often shows the +3 o ...

. The solubility of technetium(IV) oxide is very low and is reported to be 0.0000039 g/L. The main species when technetium dioxide is dissolved in water is TcO²⁺ at pH below 1.5, TcO(OH)⁺ pH between 1.5 and 2.5, TcO(OH)₂ pH between 2.5 and 10.9, and TcO(OH)₃^– above pH 10.9. The solubility can be affected by adding various organic ligands such as

humic acid Humic substances (HS) are organic compounds that are important components of humus, the major organic fraction of soil, peat, and coal (and also a constituent of many upland streams, dystrophic lakes, and ocean water). For a long era in the 19th ...

and

EDTA Ethylenediaminetetraacetic acid (EDTA) is an aminopolycarboxylic acid with the formula H2N(CH2CO2H)2sub>2. This white, water-soluble solid is widely used to bind to iron (Fe2+/Fe3+) and calcium ions (Ca2+), forming water-soluble complexes eve ...

, or by the addition of

. This can be a problem if technetium(IV) oxide is released into the soil, as it will increase the solubility. If technetium dioxide is electrolyzed in acidic conditions, the following reaction occurs: :TcO₂·2H₂O → TcO₄^– + 4 H⁺ + 3 e^– The

electrode potential In electrochemistry, electrode potential is the electromotive force of a galvanic cell built from a standard reference electrode and another electrode to be characterized. By convention, the reference electrode is the standard hydrogen electrode (S ...

measured for this reaction is -837.2 ± 10.0 kJ/mol. The molar

magnetic susceptibility In electromagnetism, the magnetic susceptibility (Latin: , "receptive"; denoted ) is a measure of how much a material will become magnetized in an applied magnetic field. It is the ratio of magnetization (magnetic moment per unit volume) to the ap ...

of TcO₂·2H₂O was found to be χ_m = 244 × 10⁶.

References

{{Oxides Technetium compounds Oxides