View source for Palladium(II) chloride

{{chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 431915305
| Name = Palladium(II) chloride
| ImageFile = Palladium chloride.jpg
| ImageName = Palladium(II) chloride<br/>Palladium dichloride
| ImageFile2 = Palladium(II)-chloride-3D-vdW.png
| ImageFile3 = Palladium(II)-chloride-3D-balls.png
| OtherNames = Palladium dichloride, Palladous chloride
|Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 7647-10-1
| UNII_Ref = {{fdacite|changed|FDA}}
| UNII = N9214IR8N7
| EINECS = 231-596-2
| RTECS = RT3500000
| PubChem = 24290
| SMILES = Cl[Pd]Cl
| SMILES_Comment = monomer
| SMILES1 = [Cl+]0[Pd-2]12[Cl+][Pd-2]34[Cl+][Pd-2]05[Cl+][Pd-2]6([Cl+]1)[Cl+][Pd-2]([Cl+]2)([Cl+]3)[Cl+][Pd-2]([Cl+]4)([Cl+]5)[Cl+]6
| SMILES1_Comment = hexamer
| InChI = 1S/2ClH.Pd/h2*1H;/q;;+2/p-2
| InChIKey = PIBWKRNGBLPSSY-UHFFFAOYSA-L
|  ChemSpiderID = 22710

  }}
|Section2={{Chembox Properties
| Formula = PdCl<sub>2</sub>
| MolarMass = 177.326 g/mol (anhydrous) <br> 213.357 g/mol (dihydrate)
| Appearance = dark red solid <br> [[hygroscopic]] (anhydrous) <br> dark brown crystals (dihydrate)
| Density = 4.0 g/cm<sup>3</sup>
| Solubility = soluble in trace amounts, better solubility in cold water
| SolubleOther = soluble in [[organic solvents]] <br> dissolves rapidly in [[hydrochloric acid|HCl]]
| MeltingPtC = 679
| MeltingPt_notes = (decomposes)
| MagSus = {{val|-38.0e-6}} cm<sup>3</sup>/mol
  }}
|Section3={{Chembox Structure
| Coordination = square planar
| CrystalStruct = rhombohedral
  }}
|Section4={{Chembox Thermochemistry
| DeltaHf = 
| Entropy = 
  }}
|Section7={{Chembox Hazards
| ExternalSDS = 
| MainHazards = 
| NFPA-H = 
| NFPA-F = 
| NFPA-R = 
| NFPA-S =
| HPhrases = {{HPhrases|}}
| PPhrases = {{PPhrases|}}
| GHS_ref = 
| FlashPt = Non-flammable
| PEL = 
| LD50 = 2704 mg/kg (rat, oral)
  }}
|Section8={{Chembox Related
| OtherAnions = [[Palladium(II) fluoride]]<br/>[[Palladium(II) bromide]]<br/>[[Palladium(II) iodide]]
| OtherCations = [[Nickel(II) chloride]]<br/>[[Platinum(II) chloride]]<br/>[[Platinum(II,IV) chloride]]<br/>[[Platinum(IV) chloride]]
  }}
}}

'''Palladium(II) chloride''', also known as '''palladium dichloride''' and '''palladous chloride''', are the [[chemical compound]]s with the [[chemical formula|formula]] PdCl<sub>2</sub>. PdCl<sub>2</sub> is a common starting material in [[palladium]] chemistry – palladium-based catalysts are of particular value in [[organic synthesis]]. It is prepared by the reaction of [[chlorine]] with palladium metal  at high temperatures.

==Structure==
Two forms of PdCl<sub>2</sub> are known, denoted α and β. In both forms, the palladium centres adopt a square-planar coordination geometry that is characteristic of Pd(II). Furthermore, in both forms, the Pd(II) centers are linked by μ<sub>2</sub>-chloride [[bridging ligand|bridge]]s.  The α-form of PdCl<sub>2</sub> is a [[polymer]], consisting of "infinite" slabs or chains. The β-form of PdCl<sub>2</sub> is [[molecular]], consisting of an [[octahedral cluster]] of six Pd atoms. Each of the twelve edges of this octahedron is spanned by Cl<sup>−</sup>.  [[Platinum(II) chloride|PtCl<sub>2</sub>]] adopts similar structures, whereas [[Nickel(II) chloride|NiCl<sub>2</sub>]] adopts the [[Cadmium chloride|CdCl<sub>2</sub>]] motif, featuring hexacoordinated Ni(II).<ref>Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. {{ISBN|0-12-352651-5}}.</ref>

[[Image:Beta-PdCl2.png|thumb|left|400px|Evolution of β-PdCl<sub>2</sub> structure: Start with cubic lattice, remove corner and centered lattice points, inscribe octahedron (red lines), label corners as X (twelve Cl<sup>−</sup> centers) and face-centered atoms as M (six Pd(II) centers).]]

{| class="wikitable" style="margin:1em auto; text-align:center;"
|[[File:Alpha-palladium(II)-chloride-xtal-3D-balls.png|250px]]||[[File:Pd6Cl12-from-xtal-1996-CM-3D-ellipsoids.png|150px]]
|-
|<small>[[ball-and-stick model]] of the<br />crystal structure of α-PdCl<sub>2</sub></small>||<small>[[thermal ellipsoid]] model of the Pd<sub>6</sub>Cl<sub>12</sub> molecule<br />found in the crystal structure of β-PdCl<sub>2</sub></small>
|}

Two further [[Polymorphism (materials science)|polymorphs]], γ-PdCl<sub>2</sub> and δ-PdCl<sub>2</sub>, have been reported and show [[negative thermal expansion]]. The high-temperature δ form contains planar ribbons of edge-connected PdCl<sub>4</sub> squares, like α-PdCl<sub>2</sub>. The low-temperature γ form has corrugated layers of corner-connected PdCl<sub>4</sub> squares.<ref>{{cite journal | author = J. Evers, W. Beck, M. Göbel, S. Jakob, P. Mayer, G. Oehlinger, M. Rotter, [[Thomas M. Klapötke|T. M. Klapötke]] | title = The Structures of δ-PdCl<sub>2</sub> and γ-PdCl<sub>2</sub>: Phases with Negative Thermal Expansion in One Direction | doi = 10.1002/anie.201000680 | journal = [[Angewandte Chemie|Angew. Chem. Int. Ed.]] | year = 2010 | volume = 49 | pages = 5677–5682 | issue = 33 | pmid = 20602377 }}</ref>

==Preparation==
Palladium(II) chloride is prepared by dissolving palladium metal in [[aqua regia]] or [[hydrochloric acid]] in the presence of [[chlorine]]. Alternatively, it may be prepared by heating palladium [[sponge metal]] with chlorine gas at 500&nbsp;°C.<ref>{{cite book |last1=Patnaik |first1=Pradyot |title=Handbook of inorganic chemicals |date=2003 |publisher=McGraw-Hill |location=New York |isbn=978-0-07-049439-8 |page=687 |edition=1 |chapter=Palladium}}</ref><ref>{{cite book |last1=Patnaik |first1=Pradyot |title=Handbook of inorganic chemicals |date=2003 |publisher=McGraw-Hill |location=New York |isbn=978-0-07-049439-8 |pages=688–689 |edition=1 |chapter=Palladium Dichloride}}</ref><ref>{{cite book |last1=Armarego |first1=W. L. F. |title=Purification of laboratory chemicals |date=2017 |publisher=Elsevier |location=Amsterdam |isbn=978-0-12-805457-4 |page=687 |edition=Eighth |chapter=4. Purification of Inorganic and Metal-Organic Chemicals}}</ref><ref>{{cite journal |last1=Kharasch |first1=Morris S. |last2=Seyler |first2=Ralph C. |last3=Mayo |first3=Frank R. |title=Coördination Compounds of Palladous Chloride |journal=J. Am. Chem. Soc. |date=1938 |volume=60 |issue=4 |pages=882–884 |doi=10.1021/ja01271a035 |publisher=American Chemical Society}}</ref>

==Reactions==
Palladium(II) chloride is a common starting point in the synthesis of other palladium compounds. It is not particularly soluble in water or non-coordinating solvents, so the first step in its utilization is often the preparation of labile but soluble Lewis base [[adduct]]s, such as [[bis(benzonitrile)palladium dichloride]] and [[bis(acetonitrile)palladium dichloride]].<ref>{{cite book | chapter = Bis(Benzonitrile)Dichloro Complexes of Palladium and Platinum | pages =60–63 | journal = [[Inorg. Synth.]] | volume = 28 | author = Gordon K. Anderson, Minren Lin | title =Inorganic Syntheses | doi = 10.1002/9780470132593.ch13 | date =2007 | isbn =9780470132593 }}</ref> These complexes are prepared by treating PdCl<sub>2</sub> with hot solutions of the nitriles:
:PdCl<sub>2</sub> + 2 RCN  → PdCl<sub>2</sub>(RCN)<sub>2</sub>

Although occasionally recommended, [[air-free technique|inert-gas techniques]] are not necessary if the complex is to be used ''in situ''. As an example, [[bis(triphenylphosphine)palladium(II) dichloride]] may be prepared from palladium(II) chloride by reacting it with [[triphenylphosphine]] in benzonitrile:<ref>{{OrgSynth | title = Palladium-catalyzed reaction of 1-alkenylboronates with vinylic halides: (1''Z'',3''E'')-1-Phenyl-1,3-octadiene | collvol = 8 | collvolpages = 532|author1-link=Norio Miyaura | author1 = Norio Miyaura|author2-link=Akira Suzuki (chemist)| author2= Akira Suzuki | year = 1993 | prep = cv8p0532}}</ref>

:PdCl<sub>2</sub> + 2 PPh<sub>3</sub> → PdCl<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>

Further reduction in the presence of more triphenylphosphine gives [[tetrakis(triphenylphosphine)palladium(0)]]; the second reaction may be carried out without purifying the intermediate dichloride:<ref>{{cite book | journal = [[Inorg. Synth.]] | volume = 13 | pages = 121–124 | author = D. R. Coulson | doi = 10.1002/9780470132449.ch23 | year = 1972 | last2 = Satek | first2 = L. C. | last3 = Grim | first3 = S. O.| title = Inorganic Syntheses | chapter = Tetrakis(triphenylphosphine)palladium(0) | isbn = 9780470132449 }}</ref>

:PdCl<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>  +  2 PPh<sub>3</sub>  +  {{sfrac|5|2}} [[Hydrazine|N<sub>2</sub>H<sub>4</sub>]]  →  Pd(PPh<sub>3</sub>)<sub>4</sub>  +  {{sfrac|1|2}} N<sub>2</sub>  +  2 [[Hydrazinium chloride|{{chem|N|2|H|5|+|Cl|-}}]]

Alternatively, palladium(II) chloride may be solubilized in the form of the [[tetrachloropalladate|tetrachloropalladate(II)]] anion, such as in [[sodium tetrachloropalladate]], by reacting with the appropriate alkali metal chloride in water:<ref name = choueiry>{{cite book | title = Handbook of Organopalladium Chemistry for Organic Synthesis | editor = Ei-ichi Negishi | isbn = 0-471-31506-0 | year = 2002 | publisher = [[John Wiley & Sons, Inc.]] | chapter = II.2.3 Pd(0) and Pd(II) Complexes Containing Phosphorus and Other Group 15 Atom Ligands | author = Daniele Choueiry and Ei-ichi Negishi | chapter-url = https://books.google.com/books?id=mTMA2hExAaIC&pg=PA47 | chapter-format = [[Google Books]] excerpt}}</ref> Palladium(II) chloride is insoluble in water, whereas the product dissolves:

: PdCl<sub>2</sub> + 2 MCl → M<sub>2</sub>PdCl<sub>4</sub>

This compound may also further react with phosphines to give phosphine complexes of palladium.<ref name = choueiry/>

Palladium chloride may also be used to give heterogeneous palladium catalysts: palladium on [[barium sulfate]], [[palladium on carbon]], and palladium chloride on carbon.<ref>{{OrgSynth | title = Palladium Catalysts | author = Ralph Mozingo | collvol = 3 | collvolpages = 685 | year = 1955 | prep = cv3p0685}}</ref>

[[File:Tetrachloropalladate ions in aqueous solution.jpg|thumb|250px|left|A solution of [PdCl<sub>4</sub>]<sup>2−</sup>(aq)]]

==Uses==
Even when dry, palladium(II) chloride is able to rapidly stain [[stainless steel]]. Thus, palladium(II) chloride solutions are sometimes used to test for the [[corrosion]]-resistance of stainless steel.<ref>For example, http://www.marinecare.nl/assets/Uploads/Downloads/Leaflet-Passivation-Test-Kit.pdf{{dead link|date=March 2018 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

Palladium(II) chloride is sometimes used in [[carbon monoxide]] detectors. Carbon monoxide reduces palladium(II) chloride to palladium:

: PdCl<sub>2</sub> + CO + H<sub>2</sub>O → Pd + CO<sub>2</sub> + 2HCl

Residual PdCl<sub>2</sub> is converted to red [[palladium iodide|PdI<sub>2</sub>]], the concentration of which may be determined colorimetrically:<ref>{{cite journal | author = T. H. Allen, W. S. Root | title = Colorimetric Determination of Carbon Monoxide in Air by an improved Palladium Chloride Method | url = http://www.jbc.org/content/216/1/309 | journal = [[J. Biol. Chem.]] | year = 1955 | volume = 216 | pages = 309–317 | pmid = 13252030 | issue = 1| doi = 10.1016/S0021-9258(19)52307-9 | doi-access = free }}</ref>

: PdCl<sub>2</sub> + 2 KI → PdI<sub>2</sub> + 2 KCl

Palladium(II) chloride is used in the [[Wacker process]] for production of [[aldehyde]]s and [[ketone]]s from [[alkene]]s.

Palladium(II) chloride can also be used for the cosmetic tattooing of [[Cornea#Function|leukomas]] in the [[cornea]].

==References==
{{reflist}}

{{Palladium compounds}}
{{Chlorides}}

[[Category:Palladium compounds]]
[[Category:Chlorides]]
[[Category:Platinum group halides]]