Gadolinium(III) chloride
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2008-06-23T20:31:00Z
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| ImageFile =
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| IUPACName =
| OtherNames = Gadolinium trichloride
| Section1 = {{Chembox Identifiers
| CASNo = 10138-52-0
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| SMILES =
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| Section2 = {{Chembox Properties
| Formula = GdCl<sub>3</sub>
| MolarMass = 263.61 g/mol
| Appearance =
| Density = 4.52 g/cm<sup>3</sup>
| MeltingPt = 609 °C
| BoilingPt = 1580 °C
| Solubility = soluble
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| Section3 = {{Chembox Hazards
| MainHazards =
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'''Gadolinium(III) chloride''', also known as '''gadolinium trichloride''', is '''GdCl<sub>3</sub>'''. It is a colorless, hygroscopic, water-soluble solid. The [[hexahydrate]] GdCl<sub>3</sub>∙6H<sub>2</sub>O is commonly encountered and is sometimes also called gadolinium trichloride. Gd<sup>3+</sup> 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 Gd<sup>3+</sub> a useful component in NMR spectroscopy and MRI.
==Preparation==
GdCl<sub>3</sub> is usually prepared by the "[[ammonium chloride]]" route, which involves the initial synthesis of (NH<sub>4</sub>)<sub>2</sub>[GdCl<sub>5</sub>]. This material can be prepared from the common starting materials at reaction temperatures of 230 °C from [[gadolinium oxide]]:
::10 NH<sub>4</sub>Cl + Gd<sub>2</sub>O<sub>3</sub> → 2 (NH<sub>4</sub>)<sub>2</sub>[GdCl<sub>5</sub>] + 6 NH<sub>3</sub> + 3 H<sub>2</sub>O <br>
from hydrated gadolinium chloride:
::4 NH<sub>4</sub>Cl + 2 GdCl<sub>3</sub>∙6H<sub>2</sub>O → 2 (NH<sub>4</sub>)<sub>2</sub>[GdCl<sub>5</sub>] + 12 H<sub>2</sub>O
<!--what are (NH<sub>4</sub>)<sub>2</sub>[GdCl<sub>5</sub>] and NH<sub>4</sub>[Gd<sub>2</sub>Cl<sub>7</sub>]?-The Corbett reference refers to them as complex chlorides.-->
from [[gadolinium]] metal:
::10 NH<sub>4</sub>Cl + 2 Gd → 2 (NH<sub>4</sub>)<sub>2</sub>[GdCl<sub>5</sub>] + 6 NH<sub>3</sub> + 3 H<sub>2</sub>
In the second step the pentachloride is decomposed at 300 °C:
::2 (NH<sub>4</sub>)<sub>2</sub>[GdCl<sub>5</sub>] → {NH<sub>4</sub>[Gd<sub>2</sub>Cl<sub>7</sub>] + 3NH<sub>4</sub>Cl}
::{NH<sub>4</sub>[Gd<sub>2</sub>Cl<sub>7</sub>] + 3 NH<sub>4</sub>Cl} → 2 GdCl<sub>3</sub> + 4 NH<sub>4</sub>Cl
The [[ammonium chloride]] route is more popular and less expensive than other methods. GdCl<sub>3</sub> can, however, also be synthesized by the reaction of solid Gd at 600 °C in a flowing stream of [[HCl]].
::Gd + 3 HCl → GdCl<sub>3</sub> + 3/2 H<sub>2</sub>
Gadolinium(III) chloride also forms a [[hexahydrate]], GdCl<sub>3</sub>∙6H<sub>2</sub>O. The hexahydrate is prepared by gadolinium(III) oxide (or chloride) in concentrated [[hydrochloric acid|HCl]] followed by evaporation.
==Structure==
GdCl<sub>3</sub> is [[monoclinic]] with a hexagonal [[uranium(III) chloride|UCl<sub>3</sub>]] structure, as seen for other 4f trichlorides including those of [[Lanthanum|La]], [[Cerium|Ce]], [[Praseodymium|Pr]], [[Neodymium|Nd]], [[Promethium|Pm]], [[Samarium|Sm]], [[Europium|Eu]] (in contrast [[Gadolinium(III) chloride|GdCl<sub>3</sub>]] crystallizes in the [[Plutonium(III) bromide|PuBr<sub>3</sub>]] motif and the following crystallize in theYCl<sub>3</sub> motif: [[Dysprosium(III) chloride|DyCl<sub>3</sub>]], HoCl<sub>3</sub>, [[Erbium(III) chloride|ErCl<sub>3</sub>]], TmCl<sub>3</sub>, YdCl<sub>3</sub>, LuCl<sub>3</sub>, YCl<sub>3</sub>). The UCl<sub>3</sub> 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 H<sub>2</sub>O [[molecules]] and 2 Cl<sup>-</sup> [[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 Gd<sup>3+</sup> has an electronic configuration of f<sup>7</sup>. Seven is the largest number of unpaired electron spins possible for an atom, so Gd<sup>3+</sup> is a key component in the design of highly paramagnetic complexes.
<br>
To generate the relaxation agents, Gd<sup>3+</sup> sources such as GdCl<sub>3</sub>∙6H<sub>2</sub>O are converted to [[coordination complex]]es. GdCl<sub>3</sub>∙6H<sub>2</sub>O 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. GdCl<sub>2</sub>(H<sub>2</sub>O)<sub>6</sub>]<sup>+</sup>, 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 Gd<sup>3+</sup> in solution. Ligands with higher coordination numbers therefore are required. The obvious candidate is [[EDTA]]<sup>4-</sup>, 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 H<sub>5</sub>DTPA, diethylenetriaminepentaacetic acid. Chelation to the conjugate base of this ligand increases the [[solubility]] of the Gd<sup>3+</sup> at the body's neutral pH ''and'' still allows for the [[paramagnetic]] effect required for an [[MRI]] contrast agent. The DTPA<sup>5-</sup> 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)(H<sub>2</sub>O)]<sup>2-</sup> is a distorted tricapped trigonal prism.
The following is the reaction for the formation of Gd-DTPA: <br>
[[image:Gd_DTPA_rxn_(2).PNG|500px|Preparation of Gd-DTPA]]
==References==
*{{cite journal
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| pages=2068–2071
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*{{cite journal
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| title=Trichlorides of the Rare Earth Elements, Yttrium, and Scandium
| journal=Inorganic Syntheses
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| pages=39–42
| doi=10.1002/9780470132531.ch8
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*{{cite journal
| last=Meyer
| first=G.
| title=The Ammonium Chloride Route to Anhydrous Rare Earth Chlorides-The Example of YCl<sub>3</sub>
| journal=Inorganic Syntheses
| volume=25
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| doi=10.1002/9780470132562.ch35
}}<br>
*{{cite journal
| last=Raduchel
| first=B.
| coauthors=Weinmann, H. & Muhler, A.
| title=Gadolinium Chelates: Chemistry, Safety, & Behavior
| journal=Encyclopedia of Nuclear Magnetic Resonance
| volume=4
| year=1996
| month=
| pages=2166–2172
}}<br>
*{{cite journal
| last=Quill
| first=L. L.
| title=Preparation of Lanthanide Chloride Methanolates Using 2,2-Dimethoxypropane
| journal=Inorganic Chemistry
| volume=7
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| pages=1433–1435
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}}
*{{cite book
| first = P.
| last = Patnaik
| year = 2003
| title = Handbook of Inorganic Chemicals
| publisher = McGraw Hill
| location = New York
}}<br>
*{{cite book
| first = A.F.
| last = Wells
| year = 1984
| title = Structural Inorganic Chemistry
| publisher = Clarendon Press
| location = Oxford
}}<br>
*{{cite web | title=Gadolinium| work=Magnetic Resonance TIP-MRI Database| url=http://www.mr-tip.com/serv1.php?type=db1&dbs=Gadolinium| accessdate=February 22| accessyear=2006}}
*{{cite web | title=Gadolinium| work=Webelements| url=http://www.webelements.com/webelements/compounds/text/Gd/Cl3Gd1-10138520.html| accessdate=February 22 | accessyear=2006}}
==External links==
[[Category:Gadolinium compounds]]
[[Category:Chlorides]]
[[Category:Metal halides]]
[[Category:Coordination compounds]]
[[th:แกโดลิเนียม(III) คลอไรด์]]