Noble Compounds and Their Compounds

Noble Gases

First Noble Gas Compound

In 1962,Neil Bartlett reported that the first real compound of Noble gases.Bartlett and Lahman had previously used the highly oxidizing compound platinum hexafluoride to oxidize dioxygen.

$$PtF_6+O_2 \rightarrow O_2^+[PtF_6]^−$$

The PtF₆is very strong oxidizing agent and could even attract electron from molecular oxygen.The first ionization energy for $$O_2 \rightarrow O_2^+$$ is 1165 KJmol^-1,which is almost the same as the value of 1170 KJmol^-1,For $$Xe \rightarrow Xe^+$$.As the first ionization energy and the size of the cation to be formed(O₂⁺) is similar with Xe⁺,it was predicted that xenon should mix with PtF₆.Experiments showed that when PtF₆ vapour was mixed with equal volume of Xe,the gases combined immediately at room temperature to produce yellow crystalline solid.He incorrectly thought that the product obtained was Xenon hexa fluoroplatinate(V),Xe⁺[PtF₆]^-.

$$Xe+PtF_6 \rightarrow Xe^+[PtF_6]^-$$

As it is thought that the product is xenonhexafluoroplatinate(V),it was not really so.The product is little bit complicated.This reaction has since been shown to be more complicated,and the product is really [XeF]⁺[Pt₂F₁₁]^-.

$$Xe[PtF_6]+PtF_6 \xrightarrow[]{25°C}[XeF]^+[PtF_6]^++PtF_5 \xrightarrow[]{60°C} [XeF]^+[Pt_2F_11]^-$$

Xenon Difluorides,XeF₂

Preparation

i)It is prepared by heating Xenon and Fluorine in the ratio of 2:1 in a sealed nickel vessel at 400°C.On cooling the vapours,it is obtained as colourless solid.

$$Xe+F_2 \xrightarrow[]{400°C} XeF_2$$

ii)It is prepared by irradiating mixture of Xe and F₂ with light from high pressure mercury lamp.

$$Xe+F_2 \xrightarrow[mercury lamp]{light from a} XeF_2$$

iii)It is prepared by the reaction of di oxygen di fluorides on xenon at -118°C.

$$Xe+O_2F_2 \xrightarrow[]{-118°C}XeF_2+O_2$$

Properties

i)XeF₂ is a white crystalline solid at room temperature and can be sublimed.it can be stored indefinitely in a nickel or Monel metal container.

ii)Oxidizing Properties

XeF₂ can oxidise a number of compounds and is itself reduced to Xe.For example XeF₂ oxidise H₂ to HF,Cl^- to Cl₂,Ce³⁺ to Ce⁴⁺,etc.

$$XeF_2+H_2 \rightarrow 2HF+Xe$$

$$XeF_2+2HCl \rightarrow Cl_2+2HF+Xe$$

$$SO_4^2-+XeF_2+Ce_2^III(SO_4)_3 \rightarrow 2Ce^IV(SO_4)_2+Xe+F_2$$

iii)Fluorinating properties

XeF₂ is a fluorinating agent.

$$2XeF_2+2CH_2=CH_2 \rightarrow FH_2C–CH_2F+CH_3–CHF_2+2Xe$$

$$C_6H_6+XeF_2 \rightarrow C_6F_6F+Xe+HF$$

$$2NO+XeF_2 \rightarrow 2NOF+Xe$$

$$2SO_3+XeF_2 \rightarrow S_2O_6F_2+Xe$$

iv)Substitution Reaction

XeF₂ undergoes substitution reactions when treated with strong protonic acids like HSO₃F,HClO₄,CF₃COOH,etc.

$$XeF_2+2HB \rightarrow Xeβ_2+2HF$$

Here β is SO₃F^-,ClO₄^-,CH₃COO^-,etc.

v)Hydrolysis reaction(reaction with water)

XeF₂ is soluble in water but undergoes slow hydrolysis.

$$2XeF_2+2H_2O \rightarrow 2Xe+4HF+O_2$$

It is rapidly hydrolysed in an aqueous solution of alkali.

$$2XeF_2+4OH^- \rightarrow 2Xe+4F^-+2H_2O+O_2$$

vi)Formation of addition compounds

XeF₂ acts as a fluoride ion donor(lewis base) and forms complexes with covalent pentafluoride including PF₅,AsF₅,SbF₅ and the transition metal fluorides NbF₅,TaF₅,PtF₅,RuF₅,etc.These complexes(adducts) are ionic compounds.These complexes are thought to have the structure.

$$XeF_2.MF_5 or [XeF]^+[MF_6]^-$$

$$XeF_2.2MF_5 or [XeF]^+[M_2F_11]^-$$

$$2XeF_2.MF_5 or [Xe_2F_3]^+[MF_6]^-$$

vii)Action of HF

XeF₂ dissolves in HF.If XeF₂ is mixed with anhydrous HF its reactivity is greatly increased,possibly due to the formation of XeF⁺.

$$Pt+3XeF_2/HF \rightarrow PtF_6+3Xe$$

$$S_8+24XeF_2lHF \rightarrow 8SF_6+24Xe$$

Xenon Tetrafluoride(XeF₄)

Preparation

XeF₂ is prepared by heating a mixture of xenon and fluorine in the ratio of 1:5 in a nickel vessel at 400°C and 6 atmospheric pressure.[

$$Xe+f_2 /xright arrow 400°C,680ms]{NickelVessel}XeF_4$$$$Xe+f_2 /xright arrow 400°C,680ms]{NickelVessel}XeF_4$$

Properties

i) XeF₄ is a white cyrstaline and solid at room temperature and can be sublimed readily.It is less volatile than Xef₆.It disssolve in CF₃COOH.It can be stored for and indifinite period in a nickel or monel metal container,but since XeF₄ is very susceptible to hydrolysis,even tracis of water must be excluded.

ii)Fluorinating properties

XeF₄is a strong fluorinating agent since it can fluorinate a number of compound.

$$XeF_4+2SF_4 \rightarrow Xe+2SF_6$$

$$XeF_4+Pt \rightarrow Xe+PtF_4$$

$$C_6H_6+XeF_4 \rightarrow 2C_6H_5F+2HF+Xe$$

iii)Oxidizing Properties

XeF₄ can oxidise a number of compounds and itself is reduced to Xe.For example:XeF₄ oxidises H₂ to HF,I^- to I₂,Cl^- to Cl₂,Hg to HgF₂,etc.

$$XeF_4+2H_2 \rightarrow 4HF+Xe$$

$$XeF_4+4KI \rightarrow 4KF+Xe+2I_2$$

$$XeF_4+2Hg \rightarrow 2HgF_2+Xe$$

iv)Hydrolysis Reaction(reaction with water)

XeF₄ reacts violently with water to form a highly explosive solid compound,XeO₃.

$$6XeF_4+12H_2O \rightarrow 4Xe+2XeO_3+24HF+3O_2$$

Hydrolysis of XeF₄ at -80°C given Xenon oxydifluoride XeOF₂.

$$XeF_4+H_2O \xrightarrow[]{-80°C}XeOF_2+2HF$$

v)Formation of complex compound

XeF₄ forms complex compounds with covalent pentafluorides like PF₅,AsF₅,SbF₅.

$$XeF_4+SbF_5 \rightarrow XeF_4.SbF_5 or [XeF_3]^+[SbF_6]^-$$

Xenon Hexafluoride(XeF₆)

Preparation

i)XeF₆ is prepared by heating a mixture of Xenon and fluorine in the ratio 1:20 in a sealed nickel vessel.

$$Xe+F_2 \rightarrow XeF_6$$

ii)XeF₆ is also prepared by the reaction of XeF₄ with O₂F₂ at -130°C.

$$XeF_4+O_2F_2 \rightarrow O_2+XeF_6$$

Properties

i)XeF₆ is white solid and can be sublimed at room temperature.It can be stored undefinitely in nickel or monel metal comtainers,but since XeF₆ is more susceptible to hydrolysis even traces of water must be excluded.It is best stored in nickel container,since it attacks glass and silica(SiO₂).

$$2XeF_6+SiO_2 \rightarrow 2XeOF_4+SiF_4$$

ii)Fluorinating Agent

Out og the three xenon fluorides,XeF₆ is the best fluorinating agent.

iii)Oxidizing properties

XeF₆ can oxidise a number of compounds and is itself reduce to Xe.

$$XeF_6+3H_2 \rightarrow 6HF+Xe$$

$$XeF_6+6HCl \rightarrow 3Cl_2+6HF+Xe$$

iv)Hydrolysis Reaction

XeF₆ reacts violently with water,but slow hydrolysis of XeF₆ by atmospheric moisture gives the highly explosive solid XeO₃.

$$XeF_6+3H_2O \rightarrow XeO_3+6HF$$

Small quantities of water bring about partial hydrolysis of XeF₆ to give colourless liquid xenon oxyfluoride(XeOF₄).

$$XeF_6+H_2O \rightarrow XeOF_4+2HF$$

v)Formation of complexes

XeF₄ can act as a fluoride ion donor forming complexes such as.

$$XeF_6.BF_3 or [XeF_5]^+[BF_4]^-$$

$$XeF_6.GeF_4 or [XeF_5]^+[GeF_5]^-$$

$$XeF_6.SbF_5$$

$$XeF_6.AsF_5$$

However,there are many reaction in which XeF₆ acts as F^- ion acceptor.with RbF and CsF it reacts as follows.

$$XeF_6+RbF \rightarrow Rb^+[XeF_4]^-$$

On heating,the [XeF₇^-] ion decompose to octafluoroxenate(VI)

$$2Cs+[XeF_7]^- \xrightarrow[]{50°C} XeF_6+CS_2^+[XeF_8]^-$$

vi)Action of heat

On strong heating,XeF₆ decomposes to give XeF₂ and XeF₄.

$$2XeF_6 \xrightarrow[]{Δ} XeF_2+XeF_4$$

vii)Reaction with HF

XeF₆ reacts with HF and forms [XeF₅]⁺[HF₂]^- which is ionic compound.

$$HF+XeF_6 \rightarrow [XeF_5]^-[HF_2]^-$$

Xenon Trioxide,XeO₃

Preparation

i)It can be obtained in small quantity by the hydrolysis of XeF₂ or XeF₄.

$$6XeF_4+12H_2O \rightarrow 4Xe+2XeO_3+12HF+3O_2$$

$$XeF_6+3H_2O \rightarrow XeO_3+6HF$$

ii)It can also be prepared by hydrolysing XeOF₄.

$$XeOF_4+2H_2O \rightarrow 4HF+XeO_3$$

iii)It can be prepared by allowing the reaction between XeF₆ and Quartz(SiO₂) to run for a prolonged period.

$$XeF_6+SiO_2 \rightarrow 2XeOF_4+SiF_4$$

$$XeOF_4+SiO_2 \rightarrow SiF_4+XeO_3]×2$$

$$\overline{XeF_6+3SiO_2 \rightarrow 3SiF_4+2XeO_3}$$

Properties

i)XeO₃ is a white non-volatile hygroscopic solid and soluble in water.It explodes,when dry,on gentle heating,rubbbing pressing,it produces the same effect at T.N.T.

ii)Its aqueous solution is weakly acidic,since it gives xenic acid in water.

$$XeO_3+H_2O \rightarrow H_2XeO_4 \rightarrow H^++HXeO^−_4$$₆

iii)Reaction with NaOH

In alkaline solution above pH 10.5,XeO₃ forms the xenate ion [HXeO₄]^-.XeO₃ reacts with NaOH to give sodiumxenate.

$$XeO_3+NaOH \rightarrow Na^+[HXeO_4]^-$$

Xenates contain Xe(+IV) and they slow disproportionate in alkaline solution to perxenates,which contain Xe(+VIII) and Xe.

$$2Na^+[HXeO_4]^-+2NaOH \rightarrow Na^+[XeO_6]^4-+Xe+O_2+2H_2O$$

iv)XeO₃ reacts with XeF₆ and XeF₄.

$$XeO_3+2XeF_6 \rightarrow 2XeOF_4$$

$$XeO_3+XeOF_4 \rightarrow 2XeO_2F_2$$

Xenon oxytetra Fluoride,XeOF₄

Preparation

i)It is prepared by the controlled hydrolysis of XeF₆ with equimolar quantity of water.

$$XeF_6+H_2O \rightarrow XeOF_4+2HF$$

ii)It can be prepared by heating XeF₆ in a silica tube at 50°C.When yellow colour of XeF₆ disappears,the bulb is immediately cooled with CO₂.The vapours of SiF₄ are pumped out and XeOF₄ is collected.

$$2XeO_6+SiO_2 \rightarrow 2XeOF_4+SiF_4$$

Properties

i)It is clear,colourless liquid which can be stored in nickel containers for long period of time.It reacts with silica to form XeO₃.

$$XeOF_4+SiO_2 \rightarrow SiF_4+XeO_3$$

ii)Hydrolysis

XeOF₄ undergoes hydrolysis to form XeO₃.

$$XeOF_4+2H_2O \rightarrow 4HF+XeO_3$$

iii)With XeO₃,XeOF₄ gives XeO₂F₂.

$$XeO_3+XeOF_4 \rightarrow 2XeO_2F_2$$

References

Poudel, Bhoj Raj Poudel and Dr.Megh Raj. A Text Book Of Inorganic Chemistry. Kathmandu: National Book Centre, 2012.

Sons, John Wiley and. J.D Lee Concise Inorganic Chemistry. 2007.