Gadolinium(III) chloride 2694405 221275166 2008-06-23T20:31:00Z DOI bot 6652755 Citation maintenance. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]]. {{Chembox new | ImageFile = | ImageSize = | IUPACName = | OtherNames = Gadolinium trichloride | Section1 = {{Chembox Identifiers | CASNo = 10138-52-0 | PubChem = | SMILES = }} | 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 }} | Section3 = {{Chembox Hazards | MainHazards = | FlashPt = | Autoignition = }} }} '''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 | last=Aime | first=S. | title=Synthesis and Characterization of a Novel DPTA-like Gadolinium(III) Complex: A Potential Reagent for the Determination of Glycated Proteins by Water Proton NMR Relaxation Measurements | journal=Inorganic Chemistry | volume=32 | year=1993 | month= | pages=2068–2071 | doi=10.1021/ic00062a031 }}<br> *{{cite journal | last=Corbett | first=John D. | title=Trichlorides of the Rare Earth Elements, Yttrium, and Scandium | journal=Inorganic Syntheses | volume=22 | year=1983 | month= | pages=39–42 | doi=10.1002/9780470132531.ch8 }}<br> *{{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 | year=1989 | month= | pages=146–150 | 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 | year=1967 | month= | pages=1433–1435 | doi=10.1021/ic50053a032 }} *{{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]]