chemistry

Gadolinium(III) chloride

Gadolinium(III) chloride is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Gadolinium(III) chloride rather than just read about it. In short: Gadolinium(III) chloride, also known as gadolinium trichloride, is GdCl3. It is a colorless, hygroscopic, water-soluble salt.

Key takeaways

Gadolinium(III) chloride belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Gadolinium(III) chloride to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Gadolinium(III) chloride from memory before moving on to harder problems.

Reference excerpt

Gadolinium(III) chloride, also known as gadolinium trichloride, is GdCl3. It is a colorless, hygroscopic, water-soluble salt. The hexahydrate GdCl3∙6H2O is commonly encountered and is sometimes also called gadolinium trichloride. Gd3+ species are of special interest because the ion has the maximum number of unpaired spins possible, at least for known elements. With seven valence electrons and seven available f-orbitals, all seven electrons are unpaired and symmetrically arranged around the metal. The high magnetism and high symmetry combine to make Gd3+ a useful component in NMR spectroscopy and MRI.

Preparation GdCl3 is usually prepared by the "ammonium chloride" route, which involves the initial synthesis of (NH4)2[GdCl5]. This material can be prepared from the common starting materials at reaction temperatures of 230 °C from gadolinium oxide:

10 NH4Cl + Gd2O3 → 2 (NH4)2[GdCl5] + 6 NH3 + 3 H2O from hydrated gadolinium chloride:

4 NH4Cl + 2 GdCl3∙6H2O → 2 (NH4)2[GdCl5] + 12 H2O from gadolinium metal:

10 NH4Cl + 2 Gd → 2 (NH4)2[GdCl5] + 6 NH3 + 3 H2 In the second step the pentachloride is decomposed at 300 °C:

(NH4)2[GdCl5] → GdCl3 + 2 NH4Cl This pyrolysis reaction proceeds via the intermediacy of NH4[Gd2Cl7]. The ammonium chloride route is more popular and less expensive than other methods. GdCl3 can, however, also be synthesized by the reaction of solid Gd at 600 °C in a flowing stream of HCl.

Gd + 3 HCl → GdCl3 + 3/2 H2 Gadolinium(III) chloride also forms a hexahydrate, GdCl3∙6H2O. The hexahydrate is prepared by gadolinium(III) oxide (or chloride) in concentrated HCl followed by evaporation.

Structure GdCl3 crystallizes with a hexagonal UCl3 structure, as seen for other 4f trichlorides including those of La, Ce, Pr, Nd, Pm, Sm, Eu. The following crystallize in theYCl3 motif: DyCl3, HoCl3, ErCl3, TmCl3, YdCl3, LuCl3, YCl3). The UCl3 motif features 9-coordinate metal with a tricapped trigonal prismatic coordination sphere. In the hexahydrate of gadolinium(III) chloride and other smaller 4f trichlorides and tribromides, six H2O molecules and 2 Cl− ions coordinate to the cations resulting in a coordination group of 8.

Properties, with applications to MRI Gadolinium salts are of primary interest for relaxation agents in magnetic resonance imaging (MRI). This technique exploits the fact that Gd3+ has an electronic configuration of f7. Seven is the largest number of unpaired electron spins possible for an atom, so Gd3+ is a key component in the design of highly paramagnetic complexes. To generate the relaxation agents, Gd3+ sources such as GdCl3∙6H2O are converted to coordination complexes. GdCl3∙6H2O can not be used as an MRI contrasting agent due to its low solubility in water at the body's near neutral pH. "Free" gadolinium(III), e.g. [GdCl2(H2O)6]+, is toxic, so chelating agents are essential for biomedical applications. Simple monodentate or even bidentate ligands will not suffice because they do not remain bound to Gd3+ in solution. Ligands with higher coordination numbers therefore are required. The obvious candidate is EDTA4−, ethylenediaminetetraacetate, which is a commonly employed hexadentate ligand used to complex to transition metals. In lanthanides, however, exhibit coordination numbers greater than six, so still larger aminocarboxylates are employed. One representative chelating agent is H5DTPA, diethylenetriaminepentaacetic acid. Chelation to the conjugate base of this ligand increases the solubility of the Gd3+ at the body's neutral pH and still allows for the paramagnetic effect required for an MRI contrast agent. The DTPA5− ligand binds to Gd through five oxygen atoms of the carboxylates and three nitrogen atoms of the amines. A 9th binding site remains, which is occupied by a water molecule. The rapid exchange of this water ligand with bulk water is a major reason for the signal enhancing properties of the chelate. The structure of [Gd(DTPA)(H2O)]2− is a distorted tricapped trigonal prism. The following is the reaction for the formation of Gd-DTPA:

References

"Gadolinium". Magnetic Resonance TIP-MRI Database. Retrieved February 22, 2006. "Gadolinium". Webelements. Retrieved February 22, 2006.

Illustrations

Worked examples

Example 1 — a first encounter with Gadolinium(III) chloride

Start with the simplest possible case. Write down what Gadolinium(III) chloride claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Gadolinium(III) chloride before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Gadolinium(III) chloride ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Gadolinium(III) chloride

In research: Gadolinium(III) chloride appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Gadolinium(III) chloride in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Gadolinium(III) chloride is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chlorides, Coordination complexes, Gadolinium compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Gadolinium(III) chloride outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Gadolinium(III) chloride in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Gadolinium(III) chloride means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
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Frequently asked questions

What is Gadolinium(III) chloride in simple terms?

Gadolinium(III) chloride, also known as gadolinium trichloride, is GdCl3. It is a colorless, hygroscopic, water-soluble salt.

Why does Gadolinium(III) chloride matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Gadolinium(III) chloride?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Gadolinium(III) chloride.