Promethium compounds are compounds containing the element

promethium Promethium is a chemical element with the symbol Pm and atomic number 61. All of its isotopes are radioactive; it is extremely rare, with only about 500–600 grams naturally occurring in Earth's crust at any given time. Promethium is one of onl ...

, which normally take the +3 oxidation state. Promethium belongs to the

cerium group The rare-earth elements (REE), also called the rare-earth metals or (in context) rare-earth oxides or sometimes the lanthanides (yttrium and scandium are usually included as rare earths), are a set of 17 nearly-indistinguishable lustrous silv ...

of lanthanides and is chemically very similar to the neighboring elements. Because of its instability, chemical studies of promethium are incomplete. Even though a few compounds have been synthesized, they are not fully studied; in general, they tend to be pink or red in color.promethium
Encyclopædia Britannica Online Treatment of acidic solutions containing Pm³⁺ ions with ammonia results in a gelatinous light-brown sediment of hydroxide, Pm(OH)₃, which is insoluble in water. When dissolved in hydrochloric acid, a water-soluble yellow salt, PmCl₃, is produced; similarly, when dissolved in nitric acid, a nitrate results, Pm(NO₃)₃. The latter is also well-soluble; when dried, it forms pink crystals, similar to Nd(NO₃)₃. The electron configuration for Pm³⁺ is e4f⁴, and the color of the ion is pink. The ground state term symbol is ⁵I₄. The sulfate is slightly soluble, like the other cerium group sulfates. Cell parameters have been calculated for its octahydrate; they lead to conclusion that the density of Pm₂(SO₄)₃·8 H₂O is 2.86 g/cm³. The oxalate, Pm₂(C₂O₄)₃·10 H₂O, has the lowest solubility of all lanthanide oxalates. Unlike the nitrate, the

oxide An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...

is similar to the corresponding samarium salt and not the neodymium salt. As-synthesized, e.g. by heating the oxalate, it is a white or lavender-colored powder with disordered structure. This powder crystallizes in a cubic lattice upon heating to 600 °C. Further annealing at 800 °C and then at 1750 °C irreversibly transforms it to monoclinic and hexagonal phases, respectively, and the last two phases can be interconverted by adjusting the annealing time and temperature. Promethium forms only one stable oxidation state, +3, in the form of ions; this is in line with other lanthanides. According to its position in the

periodic table The periodic table, also known as the periodic table of the (chemical) elements, is a rows and columns arrangement of the chemical elements. It is widely used in chemistry, physics, and other sciences, and is generally seen as an icon of ch ...

, the element cannot be expected to form stable +4 or +2 oxidation states; treating chemical compounds containing Pm³⁺ ions with strong oxidizing or reducing agents showed that the ion is not easily oxidized or reduced.

References

{{Chemical compounds by element Promethium Promethium compounds Chemical compounds by element