Tantalum(V) chloride: Difference between revisions

| verifiedrevid = 411541570

| Name = Tantalum(V) chloride

| IUPACName = Tantalum(V) chloride<br/>Tantalum pentachloride

| ImageFile=TaCl5structure.jpg

| Section1 = {{Chembox Identifiers

| CASNo = 7721-01-9

| CASNo_Ref = {{cascite}}

| EINECS =

| RTECS =

| Section2 = {{Chembox Properties

| Formula = TaCl₅

| Appearance = white [[monoclinic]] crystals<ref>{{RubberBible87th}}</ref>

| MolarMass = 358.21 g/mol

| Solubility = reacts

| Solvent =

| SolubleOther = soluble in [[ethanol]], [[ether]], [[carbon tetrachloride|CCl₄]]

| MeltingPt = 216 °C

| BoilingPt = 239.4 °C (decomp)

| Section3 = {{Chembox Structure

| CrystalStruct = [[Monoclinic]], [[Pearson symbol|mS72]]

| SpaceGroup = C2/m, No. 12

| Section4 = {{Chembox Thermochemistry

| DeltaHf = -858.98 kJ/mol

| Entropy = 221.75 J&thinsp;K⁻¹&thinsp;mol⁻¹

| Section7 = {{Chembox Hazards

| ExternalMSDS =

| EUIndex = Not listed

| NFPA-H =

| NFPA-F =

| NFPA-R =

| NFPA-O =

| FlashPt = Non-flammable

| Section8 = {{Chembox Related

| OtherAnions = [[Tantalum(V) fluoride]]<br/>[[Tantalum(V) bromide]]<br/>[[Tantalum(V) iodide]]

| OtherCations = [[Vanadium(IV) chloride]]<br/>[[Niobium(V) chloride]]

'''Tantalum(V) chloride''', also known as '''tantalum pentachloride''', is the [[inorganic compound]] with the formula TaCl₅. This white powder is a starting material in [[tantalum]] chemistry. It hydrolyzes readily, releasing HCl. TaCl₅ is prepared by heating tantalum metal in [[chlorine]]. Samples are often contaminated with tantalum(V) oxychloride (TaOCl₃), formed by hydrolysis.

TaCl₅ crystallizes in the monoclinic space group ''C''2/''m''.<ref>{{cite journal | author = S. Rabe, U. Müller | title = Crystal structure of tantalum pentachloride, (TaCl₅)₂ | journal = [[Z. Kristallogr. – New Cryst. Struct.]] | year = 2000 | volume = 215 | pages = 1–2}}</ref> The ten chlorine atoms define a pair of octahedra that share a common edge. The tantalum atoms occupy the centres of the octahedra and are joined by two chlorine-[[bridging ligand]]s. The dimeric structure is retained in non-complexing solvents and to a large extent in the molten state. In the vapour state, however, TaCl₅ is monomeric. This monomer adopts trigonal bipyramidal structure, like that of [[Phosphorus pentachloride|PCl₅]].<ref>{{cite book | author = F. Fairbrother | title = The Chemistry of Niobium and Tantalum | publisher = Elsevier | year = 1967}}</ref>

==Physical properties==

The solubility of tantalum pentachloride increases to a slightly for the following series of aromatic hydrocarbons: benzene< toluene< m-xylene< mesitylene, as reflected in the deepening of colour of the solutions from pale yellow to orange. Tantalum pentachloride is less soluble in cyclohexane and carbon tetrachloride than in the aromatic hydrocarbons. Such solutions of tantalum pentachloride is also known to be a poor conductor of electricity, indicating little ionization. TaCl₅ is purified by [[Sublimation (physics)|sublimation]] to give white needles.

TaCl₅ is electrophillic and it behaves like a Friedel-Crafts type catalyst, similar to AlCl₃. It forms [[adduct]]s with a variety of [[Lewis base]]s.<ref>F. A. Cotton, G. Wilkinson, ''Advanced Inorganic Chemistry'' (4th ed.), Wiley, New York, '''1980'''.</ref>

TaCl₅ forms stable complexes with ethers:

::TaCl₅ + R₂O → TaCl₅(OR₂) (R = Me, Et)

TaCl₅ also reacts with phosphorus pentachloride and phosphorus oxychloride, the former is a chloride donor and the latter serves as a ligand, binding through oxygen:

::TaCl₅ + PCl₅ → [PCl₄⁺][TaCl₆]

::TaCl₅ + OPCl₃ → [TaCl₅(OPCl₃)]

Tantalum pentachloride reacts with tertiary amines to give crystalline adducts.

::TaCl₅ + 2 R₃N → [TaCl₅(NMe₃)

Tantalum pentachloride reacts at room temperature with an excess of triphenyl phosphine oxide to give oxychlorides:

::TaCl₅ + 3 OPPh₃ → [TaOCl₃(OP(C₆H₅)₃]_x ...

The presumed initial formation of adducts between TaCl₅ and hydroxyl compounds such as alcohols, phenols and carboxylic acids is followed immediately by the elimination of hydrogen chloride and the formation of Ta-O bonds:

::TaCl₅ + 3 HOEt → TaCl₂(OEt)₃ + 3 HCl

In the presence of ammonia as an HCl acceptor, all five chloride ligands are displaced with formation of Ta(OEt)₅. Similarly TaCl₅ reacts with lithium methoxide in anhydrous methanol to form related methoxy derivatives:

::TaCl₅ + 5LiOMe → Ta(OMe)₄Cl + 4LiCl

===Ammonolysis and amide-forming reactions===

Ammonia will displace most of the chloride ligands from TaCl₅ to give a cluster. Chloride is displaced more slowly by primary or secondary amines but the replacement of all five chloride centers by amido groups has been achieved by the use of lithium dialkyamides:

::TaCl₅ + 5LiNR₂ → Ta(NR₂)₅

Tantalum pentachloride is reduced by nitrogen heterocycles such as pyridine.

* {{cite journal | author = G. A. Ozin, R. A. Walton | journal = [[J. Chem. Soc. A.]] | year = 1970 | pages = 2236–2239 | doi = 10.1039/j19700002236 | title = Vibrational spectra and structures of the 1:1 complexes of niobium and tantalum, pentachlorides and tantalum pentabromide with aceto-, perdeuterioaceto-, and propio-nitriles in the solid and solution states and a vibrational analysis of the species MX5,NC�CY3(Y = H or D)}}

* {{cite journal | author = J. I. Bullock, F. W. Parrett, N. J. Taylor | journal = [[Dalton Trans.]] | year = 1973 | pages = 522–524}}

* {{cite journal | author = C. Djordjević, V. Katović | journal = [[J. Chem. Soc. A]] | year = 1970 | pages = 3382–3386 | doi = 10.1039/j19700003382 | title = Co-ordination complexes of niobium and tantalum. Part VIII. Complexes of niobium(IV), niobium(V), and tantalum(V) with mixed oxo, halogeno, alkoxy, and 2,2?-bipyridyl ligands}}

* {{cite journal | author = A. Cowley, F. Fairbrother, N. Scott | journal = [[J. Chem. Soc. A]] | year = 1958 | pages = 3133–3137}}

[[Category:Tantalum compounds]]

[[de:Tantal(V)-chlorid]]