Samarium is a silver-white lanthanide metal used in high-strength permanent magnets (e.g., Sm–Co alloys), specialty optics, and as a neutron absorber in nuclear applications.
The ground-state configuration of samarium is [Xe] 4f6 6s2. When it forms the common +3 oxidation state (Sm3+), it loses two 6s electrons and one 4f electron, giving a 4f5 configuration. This arrangement contributes to its magnetic and optical properties.
Samarium most commonly shows the +3 oxidation state, forming compounds such as SmCl3 and Sm2O3. It can also exhibit a stable +2 oxidation state in compounds like SmI2 and SmO, where Sm2+ acts as a strong reducing agent.
Major applications of samarium include:
Samarium–cobalt (Sm–Co) magnets are rare-earth permanent magnets known for high magnetic strength, corrosion resistance, and temperature stability. They retain magnetization up to 350–550 °C, making them suitable for motors, turbines, and defense systems.
Samarium slowly oxidizes in air to form Sm2O3 and reacts slowly with water to form hydroxide and hydrogen gas:
\(\mathrm{4\,Sm(s) + 3\,O_2(g) \rightarrow 2\,Sm_2O_3(s)}\)
\(\mathrm{2\,Sm(s) + 6\,H_2O(l) \rightarrow 2\,Sm(OH)_3(s) + 3\,H_2(g)}\)
It must be stored under mineral oil or inert gas to prevent surface oxidation.
Samarium(II) iodide (SmI2) is a powerful one-electron reducing agent used in organic synthesis. It is applied in reactions such as dehalogenation, pinacol coupling, and reduction of carbonyl compounds. Its mild reactivity and selectivity make it valuable in complex molecule construction.
Samarium is paramagnetic due to unpaired 4f electrons. In Sm–Co alloys, it contributes to strong magnetic anisotropy and high coercivity. Its 4f electrons are shielded from the environment, giving stable magnetic moments even at high temperatures.
Samarium, especially isotope 149Sm, is a potent neutron absorber. It forms as a fission product in reactors and acts as a burnable poison, helping control reactivity during fuel cycles. Its stable oxide form (Sm2O3) is also used in reactor shielding materials.
Samarium(III) compounds typically appear yellow to pale brown, while Sm(II) compounds are deep red. These colors arise from 4f–4f electronic transitions, which are sharp and characteristic of rare-earth ions.
Natural samarium consists of mainly stable isotopes, with 147Sm and 149Sm being weakly radioactive (long half-lives). It poses low toxicity but fine powders may be flammable and irritating. Standard precautions (gloves, mask, fume hood) are recommended when handling Sm compounds.
Sm(II) compounds like SmI2 readily reduce halides or carbonyls. A general example is:
\(\mathrm{R{-}X + SmI_2 \rightarrow R{-}H + SmI_3}\)
This illustrates the strong reducing power of Sm(II), converting organic halides (R–X) to hydrocarbons (R–H).