Gadolinium is a silvery-white, malleable lanthanide. It is strongly paramagnetic near room temperature (ferromagnetic below its Curie point ~293 K), has a very high neutron-capture cross-section, and is used in MRI contrast agents (as chelates), control rods, and specialty alloys.
The ground-state configuration is [Xe] 4f7 5d1 6s2. The half-filled 4f7 subshell gives gadolinium extra stability and accounts for its strong magnetic properties. The additional 5d electron distinguishes it from europium, which has a pure 4f7 configuration.
Gadolinium has seven unpaired 4f electrons, leading to a large magnetic moment. It is ferromagnetic below 293 K (20 °C) and paramagnetic above that. Its magnetic susceptibility changes sharply near this Curie point, making it useful for magnetic refrigeration and temperature sensors.
The most common oxidation state is +3 (Gd3+), found in compounds such as Gd2O3 and GdCl3. The +2 oxidation state is rare but has been observed in compounds like GdI2 under reducing conditions. Gd3+ has a stable half-filled 4f7 configuration.
Gadolinium is used in several applications:
Gadolinium’s seven unpaired electrons cause strong local magnetic fields, which shorten the relaxation times of nearby hydrogen nuclei in water molecules. This enhances contrast in MRI images. However, free Gd3+ is toxic, so it is used as a chelated complex such as Gd–DTPA or Gd–DOTA for safe medical use.
Gadolinium is moderately reactive:
\(\mathrm{4\,Gd(s) + 3\,O_2(g) \rightarrow 2\,Gd_2O_3(s)}\)
\(\mathrm{2\,Gd(s) + 6\,H_2O(l) \rightarrow 2\,Gd(OH)_3(s) + 3\,H_2(g)}\)
It tarnishes slowly in dry air and more rapidly in moist air, forming a protective oxide layer.
Gadolinium has an exceptionally high neutron-capture cross-section (especially isotope 157Gd), making it useful for control rods in nuclear reactors and neutron shielding. This property helps regulate chain reactions effectively.
Important Gd compounds include:
Free gadolinium ions (Gd3+) are toxic to biological systems because they interfere with calcium ion channels. However, in medical imaging, gadolinium is administered in chelated forms (e.g., with DTPA or DOTA ligands), which bind the ion tightly and minimize toxicity. Proper elimination through the kidneys is essential for safety.
Gadolinium is the most magnetic lanthanide due to its half-filled 4f shell (seven unpaired electrons). While other lanthanides like Dy and Tb show high magnetic moments, Gd’s simple electron configuration gives it the highest magnetic ordering temperature among them.
Like most lanthanides, gadolinium forms Gd3+ ions through oxidation:
\(\mathrm{Gd(s) \rightarrow Gd^{3+}(aq) + 3e^-}\)
This redox behavior is central to the formation of gadolinium compounds and complexes used in various technologies.