nn = 5= 5 nn = 6= 6 nn =7=7 nn = 8= 8TrigonalTrigonal bipyramidbipyramid octahedronoctahedron pentagonal pentagonal bipyramidbipyramid dodecahedrondodecahedron

nn = 9= 9 nn = 10= 10 nn =11=11 nn = 12= 12TricappedTricapped trigonaltrigonal prism prism bicappedbicapped square square antiprismantiprism octadecahedronoctadecahedron icosahedronicosahedron

TheThe deltahedraldeltahedral cagescages withwith 55--1212 verticesvertices whichwhich areare thethe parentparent cagescages usedused inin conjunctionconjunction withwith Wade’sWade’srulesrules toto rationalizerationalize boraneborane clustercluster structuresstructures.. AsAs aa generalgeneral (but(but notnot foolproof)foolproof) scheme,scheme, whenwhen removingremovingthethe verticesvertices fromfrom thesethese cagescages toto generategenerate nidonido--frameworks,frameworks, removeremove aa vertexvertex connectivityconnectivity threethree fromfrom thethetrigonaltrigonal bipyramidmbipyramidm anyany vertexvertex fromfrom thethe octahedronoctahedron oror icosahedronicosahedron,, aa ‘cap’‘cap’ fromfrom thethe tricappedtricapped trigonaltrigonalprismprism oror bicappedbicapped squaresquare--antiprismantiprism,, andand aa vertexvertex ofof highesthighest connectivityconnectivity fromfrom thethe remainingremaining deltahedradeltahedra..

AA deltahedrondeltahedron (plural(plural deltahedradeltahedra)) isis aa polyhedronpolyhedron whosewhose facesfaces areare allallequilateralequilateral trianglestriangles..

BB22HH66 + Na[BH+ Na[BH44] ] �������� Na[BNa[B33HH88] + H] + H22

4Na[B4Na[B33HH88] + 4HCl ] + 4HCl �������� 3B3B44HH1010 + 3H+ 3H22 + 4NaCl+ 4NaCl

5[B5[B33HH88]]-- + 5HBr + 5HBr �������� 5[B5[B33HH77Br]Br]-- + H+ H22

363 K in 363 K in diglymediglyme

�������� 3B3B55HH99 + 4H+ 4H22 + 5Br+ 5Br--

2Na[B2Na[B33HH88] Na] Na22[B[B66HH66] + 5H] + 5H22435 K in 435 K in diglymediglyme

373 K 373 K

1-methoxy-2-(2-methoxyethoxy)ethane2-Methoxyethyl ether Di(2-methoxyethyl) ether Diethylene glycol dimethyl ether

OO

O

O

triglyme

More boron chemistry will be discussed while learning Inorganic Rings, Cages and Clusters.More boron chemistry will be discussed while learning Inorganic Rings, Cages and Clusters.

The Group 14 Elements [The Group 14 Elements [nsns22npnp22]]

FeaturesFeatures

••The periodic changes among the chemistry of these elementsThe periodic changes among the chemistry of these elements

••The stability and abundance of CThe stability and abundance of C--C bonded compoundsC bonded compounds

••The importance of The importance of ππ--bonding in carbon compoundsbonding in carbon compounds

•• Lie in the centre of the main group elementsLie in the centre of the main group elements..

•• They show major differences from the lightest element carbon (a typical nonThey show major differences from the lightest element carbon (a typical non--•• They show major differences from the lightest element carbon (a typical nonThey show major differences from the lightest element carbon (a typical non--metal) to the heaviest element lead (a typical main group metal).metal) to the heaviest element lead (a typical main group metal).

•• The group oxidation state is +4 (important for C and Si).The group oxidation state is +4 (important for C and Si).

•• In hydrocarbons the oxidation is formally In hydrocarbons the oxidation is formally --4; these compounds are 4; these compounds are thermodynamically unstable, but an extremely important class of compounds thermodynamically unstable, but an extremely important class of compounds which have constituted the branch of organic chemistrywhich have constituted the branch of organic chemistry..

• Ge shows some stable +2 compounds; GeI2, although the +4 state is predominant.

•• Tin (Tin (SnSn) shows both +2 and +4; +2 is reducing agent, whereas Pb) shows both +2 and +4; +2 is reducing agent, whereas Pb4+4+ is is oxidizing and Pboxidizing and Pb2+2+ is stable. PbOis stable. PbO22 is a powerful oxidizing agent.is a powerful oxidizing agent.

•These elements in principle should show stable 2+ oxidation state using two p-electrons. Promotion of an electron from ns2 to np requires energy, but the atom can now form four bonds. More energy produced by bond formation for C and Si offsets the cost of promoting an ns electron. Tetravalent state is very stable for C and si.

•Bond strength decreases down the group.

•Important feature of Group 14 elements is catenation which is less important down the group.

Important sources of carbon are coal and crude oil, natural gas

CatenationCatenation isis thethe formationformation ofof ringsringsandand chainschains byby atomsatoms ofof thethe samesameelementelement.. AfterAfter carbon,carbon, sulfursulfur formsformsthethe nextnext largestlargest numbernumber ofofcatenatedcatenated compoundscompounds

What factors contribute to the stability of strong CWhat factors contribute to the stability of strong C--C bonds?C bonds?

Important sources of carbon are coal and crude oil, natural gas (mainly as CH4)

Carbon shows allotropy: Graphite, diamond (crystalline forms); soot (amorphous)

a) Diamond a) Diamond b) Graphite b) Graphite c) Lonsdaleite c) Lonsdaleite d) C60 d) C60 (Buckminsterfullerene)(Buckminsterfullerene)

e) C540 Fullerene e) C540 Fullerene f) C70 Fullerene f) C70 Fullerene f) C70 Fullerene f) C70 Fullerene g) Amorphous carbon g) Amorphous carbon h) Singleh) Single--walled carbon walled carbon

nanotubenanotube

Lonsdaleite is ahexagonal allotrope ofthe carbon allotropediamond, believed toform when meteoricgraphite falls to Earth.

InIn graphite,graphite, thethe carboncarbon atomsatoms formform planarplanar sheetssheets ofof usedused sixsix--memberedmembered ringsrings (sp(sp22))..

TheThe remainingremaining ppzz orbitalsorbitals formform extensiveextensive delocalizeddelocalized ππππππππ--systemsystemoverover thethe sheetsheet..

AttractionAttraction betweenbetween adjacentadjacent sheetssheets isis weak,weak, soso thethe graphitegraphitelayerslayers slideslide overover eacheach otherother veryvery easilyeasily..

GraphiteGraphite structurestructure isis uniqueunique forfor carboncarbon amongamong GroupGroup 1414elements,elements, becausebecause thethe smallsmall ppzz orbitalsorbitals onon carboncarbon cancan overlapoverlapeffectivelyeffectively toto formform thethe delocalizeddelocalized ππππππππ--systemsystem..

InIn contrast,contrast, diamonddiamond hashas 33DD--networknetwork structurestructure builtbuilt upup fromfromInIn contrast,contrast, diamonddiamond hashas 33DD--networknetwork structurestructure builtbuilt upup fromfromtetrahedraltetrahedral carboncarbon atomsatoms formingforming strongstrong covalentcovalent bondsbonds withwitheacheach otherother.. DiamondDiamond isis thethe oneone ofof thethe hardesthardest substancessubstancesknownknown..

AnotherAnother molecularmolecular allotropesallotropes ofof carboncarbon isis calledcalled fullerenesfullerenes;;firstfirst oneone toto bebe discovereddiscovered isis CC6060 consistsconsists ofof fivefive–– andand sixsix--memberedmembered ringsrings alsoalso calledcalled asas buckyballsbuckyballs afterafter thethe architectarchitectRR.. BuckminsterBuckminster FullerFuller whowho designeddesigned geodesicgeodesic domesdomes..

The melting points of diamond and graphite are greater than 3550 The melting points of diamond and graphite are greater than 3550 ooCC, but C, but C6060 sublimes sublimes between 450 between 450 ooCC and 500 and 500 ooC.C. Explain observation.Explain observation.

Silicon, Germanium. Tin and LeadSilicon, Germanium. Tin and Lead

Silicon is the most abundant element (after oxygen) in the Earth’s crust.Silicon is the most abundant element (after oxygen) in the Earth’s crust.

Occurs as silica (SiOOccurs as silica (SiO22) and silicate minerals.) and silicate minerals.

Germanium is least common and occurs in some zinc and silver ores Germanium is least common and occurs in some zinc and silver ores and also in flue dust and the ashes of certain types of coal. and also in flue dust and the ashes of certain types of coal.

Si and Si and GeGe adopt diamondadopt diamond--like structures.like structures.

Tin mainly occurs as Tin mainly occurs as cassiteritecassiterite, SnO, SnO22 from which metallic tin is from which metallic tin is obtained by reductionobtained by reduction

The main ore of lead is galena, The main ore of lead is galena, PbSPbS, which is roasted in air to form lead , which is roasted in air to form lead oxide, which is then reduced to the metal using CO in a blast furnace. oxide, which is then reduced to the metal using CO in a blast furnace. Lead is a typical heavy metal.Lead is a typical heavy metal.

ChemistryChemistry

All Group 14 members are fairly All Group 14 members are fairly unreactiveunreactive..

Tin and lead dissolve in a number of oxidizing and nonTin and lead dissolve in a number of oxidizing and non--oxidizing acids.oxidizing acids.

Si and Si and GeGe are only attacked by HF but all are reactive towards halogens.are only attacked by HF but all are reactive towards halogens.

Graphite can form two types of products with either buckled or planar Graphite can form two types of products with either buckled or planar sheets, depending on whether the sheets, depending on whether the ππ--system is disrupted or not.system is disrupted or not.

The reaction of graphite with fluorine at 400 The reaction of graphite with fluorine at 400 ooCC gives graphite fluoride, gives graphite fluoride, The reaction of graphite with fluorine at 400 The reaction of graphite with fluorine at 400 CC gives graphite fluoride, gives graphite fluoride, ((CFCFxx))nn which is colorless when x=1. One of the possible structures which is colorless when x=1. One of the possible structures consists of fused consists of fused cyclohexanecyclohexane rings.rings.

Except for the edges of sheets (which will be CFExcept for the edges of sheets (which will be CF22 units) each carbon units) each carbon bears single F. Fluorinated graphite is nonbears single F. Fluorinated graphite is non--conducting as conducting as ππππππππ--electrons electrons are consumed. are consumed.

When graphite is reacted with a reducing agent such as an alkali metal, When graphite is reacted with a reducing agent such as an alkali metal, inclusion compounds are formed, inclusion compounds are formed, e.ge.g KCKC88 is an inclusion compound.is an inclusion compound.

8C (graphite) + K(g) 8C (graphite) + K(g) �������� KCKC88(s)(s)

660 pm

Structure of graphite fluorideStructure of graphite fluoride

Used as solid lubricators

Graphite, inter layer separation Graphite, inter layer separation 3.35 Å3.35 Å

K vaporK vapor

KCKC88

inter layer separation inter layer separation 55.40 Å.40 Å

CaCCaC66The graphite interlayer distance increases upon Ca The graphite interlayer distance increases upon Ca intercalation from 3.35 to 4.524intercalation from 3.35 to 4.524 Å, and the carbonÅ, and the carbon--carbon distance increases from 1.42 to 1.444 Å.carbon distance increases from 1.42 to 1.444 Å.

Hydrides and Organometallic CompoundsHydrides and Organometallic Compounds

Methane,Methane, CHCH44,, isis thethe simplestsimplest hydridehydride ofof carboncarbon;; thethe hydrides,hydrides, MHMH44

ofof otherother GroupGroup 1414 elementselements areare lessless stablestable owingowing toto thethe sizesizemismatchmismatch betweenbetween GroupGroup 1414 atomatom andand thethe veryvery smallsmall HH atomatom..

SilaneSilane,, germanegermane andand stannanestannane areare allall known,known, butbut plumbaneplumbane isis veryveryunstableunstable andand nono chemistrychemistry hashas beenbeen determineddetermined..

GeneralGeneral methodsmethods ofof preparationpreparation

SiClSiCl + LiAlH+ LiAlH �������� SiHSiH + LiAlCl+ LiAlCl

w

SiClSiCl44 + LiAlH+ LiAlH44 �������� SiHSiH44 + LiAlCl+ LiAlCl44

GeOGeO22 + LiAlH+ LiAlH44 �������� GeHGeH44 + LiAlO+ LiAlO33

4PhSiCl4PhSiCl33 + 3LiAlH+ 3LiAlH44 �������� 4PhSiH4PhSiH33 + 3LiAlCl+ 3LiAlCl44

Hydrocarbons are thermodynamically unstable in air; suitable activation (suchas a spark) readily ignites hydrocarbon-air mixture (octane is a fuel)

2C2C88HH1818 + 25O+ 25O22 ��������16CO16CO22 + 18H+ 18H22O + energyO + energy

Catenation is restricted to SiCatenation is restricted to Si1010HH22 22 for siliconfor silicon

GeGe99HH2020 for germanium and only Snfor germanium and only Sn22HH66 is known for tin.is known for tin.

A wide range of alkyl and aryl compounds of Si, A wide range of alkyl and aryl compounds of Si, GeGe, , SnSn and and PbPb have have been prepared (Mebeen prepared (Me33SnCl, EtSnCl, Et44Pb, an antiPb, an anti--knock additive in petrol).knock additive in petrol).

For carbon, compounds containing double and triple bonds are For carbon, compounds containing double and triple bonds are well known.well known.

(C=C, C=O, C=N, C=P. C=P); (C≡C, C≡N, C≡P)(C=C, C=O, C=N, C=P. C=P); (C≡C, C≡N, C≡P)

Pb Pb

First example of a Pb=Pb compound

Does Does tintin show multiple bonding? If show multiple bonding? If so, is it different from, say C=C??so, is it different from, say C=C??

TetrahalidesTetrahalides

MXMX44 existsexists forfor allall groupgroup members,members, exceptexcept forfor PbIPbI44whichwhich isis aa tootoo strongstrong anan oxidizingoxidizing agentagent toto coco--exitexitwithwith thethe reducingreducing iodideiodide;; samesame thingthing isis truetrue withwithPbBrPbBr44 asas wellwell..

Si +2ClSi +2Cl22 �������� SiClSiCl44

SnSn + 2I+ 2I �������� SnISnI �������� SnISnISnSn + 2I+ 2I22 �������� SnISnI22 �������� SnISnI44

GeOGeO22 + 4HBr + 4HBr �������� GeBrGeBr44 + 2H+ 2H22OO

SiClSiCl44 + excess H+ excess H22O O �������� SiOSiO22..nnHH22O + O + HClHCl

All halides (except CClAll halides (except CCl44) undergo hydrolysis except SiF) undergo hydrolysis except SiF44; kinetic ; kinetic instabilityinstability

CClCCl44 can not increase its coordination number.can not increase its coordination number.

SnSn + 2HX + 2HX �������� SnXSnX22 + H+ H22

GeXGeX44 + + GeGe �������� 2GeX2GeX22, ,

comproportionationcomproportionation reactionreaction

2GeI2GeI2 2 �������� GeIGeI44 + 2Ge, + 2Ge, disproportionationdisproportionation reactionreaction

Adduct formation by addition

of X- to SnX4

SnX4

SnX5-

X-

Cl

Sn

Cl

Gas phase

Cl

Sn

ClCl

Sn

ClCl

Sn

Cl n

Solid State

5

SnX62-

X-

SF6 is similarly stable towards hydrolysis

Propensity of carbon to form extensive stable chains is remarkable. The congeners of Propensity of carbon to form extensive stable chains is remarkable. The congeners of carbon (especially silicon) and other related noncarbon (especially silicon) and other related non--metals exhibit it to a reduced extent.metals exhibit it to a reduced extent.

Despite there is no thermodynamic barrier , formation of longDespite there is no thermodynamic barrier , formation of long--chain chain silanessilanes, Si, SinnHH2n+22n+2, , their synthesis and characterization are formidable tasks.their synthesis and characterization are formidable tasks.

Although SiAlthough Si--Si bonds are weaker than CSi bonds are weaker than C--C bonds, the energy difference do not C bonds, the energy difference do not account for the observed stability differences.account for the observed stability differences.

The reason is the lowThe reason is the low--energy decomposition pathways are available to energy decomposition pathways are available to silanessilanes which which is not available to is not available to alkanesalkanes (cracking (breaking C(cracking (breaking C--C bond) is a tough task). C bond) is a tough task).

In addition to their inherent kinetic instability, In addition to their inherent kinetic instability, silanessilanes are difficult to handle because are difficult to handle because In addition to their inherent kinetic instability, In addition to their inherent kinetic instability, silanessilanes are difficult to handle because are difficult to handle because they are very reactive.they are very reactive.

CCnnHH22nn+2+2 + + 33nn+1+1 OO22 �������� nnCOCO22 + (+ (nn+1)H+1)H22OO

SiSinnHH22nn+2+2 + + 33nn+1+1 OO22 �������� nnSiOSiO22 + (+ (nn+1)H+1)H22OO

In fact both the reactions are thermodynamically favored to proceed to the right. The In fact both the reactions are thermodynamically favored to proceed to the right. The major difference, not apparent in the major difference, not apparent in the stoichiometricstoichiometric reactions, is the energy of reactions, is the energy of activation which causes the activation which causes the paraffinsparaffins to be kinetically inert in contrast to the reactive to be kinetically inert in contrast to the reactive silanessilanes..

22

2

Further complications with Further complications with silanessilanes arise from lack of convenient synthesis and arise from lack of convenient synthesis and difficulties in separation. However, compounds difficulties in separation. However, compounds nn = 1 to = 1 to nn = 8 have been isolated, = 8 have been isolated, including straightincluding straight--chain and branchedchain and branched--chain compounds.chain compounds.

For more information read: For more information read: HeneggeHenegge, E. In Silicon Chemistry; Corey, J. Y.; Corey, E. R.; Gasper, P. P. Eds.: , E. In Silicon Chemistry; Corey, J. Y.; Corey, E. R.; Gasper, P. P. Eds.:

Wiley: New York, 1988.Wiley: New York, 1988.

Why sulfur Why sulfur catenatescatenates::

The great variety of molecular forms that can be achieved by The great variety of molecular forms that can be achieved by ––SS--S catenation .S catenation .

Numerous way in which the molecules so formed can be arranged within the Numerous way in which the molecules so formed can be arranged within the

crystal.crystal.

SS--S bonds are very variable and flexible; bond distances can vary from 180S bonds are very variable and flexible; bond distances can vary from 180--260 pm 260 pm

(single bond to multiple bond character).(single bond to multiple bond character).

Bond angles can vary from 90Bond angles can vary from 90--180180oo and dihedral angles Sand dihedral angles S--SS--SS--S from 0S from 0--180180oo..

Estimated SEstimated S--S bond energy is 430 kJ/mol and the unrestrained S bond energy is 430 kJ/mol and the unrestrained ––SS--S single bond S single bond

energy is 265 kJ/mol.energy is 265 kJ/mol.

Less tendency to stabilize S=S bonds similar to O=O.Less tendency to stabilize S=S bonds similar to O=O.

But they are not as stable as CBut they are not as stable as C--C bonded compounds.C bonded compounds.

Halides with EHalides with E--E bonds: E bonds: CatenatedCatenated HalidesHalides

Similar to extensive range of hydrocarbons, diverse range of halocarbons are Similar to extensive range of hydrocarbons, diverse range of halocarbons are known; best example being poly(known; best example being poly(tetrafluoroethenetetrafluoroethene), PTFE, an extremely ), PTFE, an extremely stable polymer finding numerous applicationsstable polymer finding numerous applications

n

FF FF

F F F F

n

F F FFFF

For silicon, a large number of higher halides are known, containing chains of For silicon, a large number of higher halides are known, containing chains of silicon atoms, analogous to the polysilanes.silicon atoms, analogous to the polysilanes.

Germanium, tin and lead form few analogues of the silicon compounds Germanium, tin and lead form few analogues of the silicon compounds because of the lower stability of the Ebecause of the lower stability of the E--E bonds going down the group, and E bonds going down the group, and the increased stability of the divalent halidesthe increased stability of the divalent halides

When carbon or silicon is heated with many metals, carbides and When carbon or silicon is heated with many metals, carbides and silicidessilicides are are formed.formed.

There are many different types of carbides, which are classified by their reaction There are many different types of carbides, which are classified by their reaction (or lack of it) with water and the products formed.(or lack of it) with water and the products formed.

Transition metals typically form interstitial carbide compounds, in which the Transition metals typically form interstitial carbide compounds, in which the individual carbon atoms occupy holes in closeindividual carbon atoms occupy holes in close--packed metallic lattices.packed metallic lattices.

These materials are also very hard.These materials are also very hard.

Some interstitial carbides Some interstitial carbides hydrolysehydrolyse to give hydrogen and hydrocarbons, but to give hydrogen and hydrocarbons, but others such as tungsten carbide (WC) are very hard, inert materialsothers such as tungsten carbide (WC) are very hard, inert materials

The carbides of reactive metals tend to be ionic in nature; some carbides (e.g. The carbides of reactive metals tend to be ionic in nature; some carbides (e.g. NaNa44C, BeC, Be22C) formally contain CC) formally contain C44-- ions and give methane on hydrolysis.ions and give methane on hydrolysis.

Other contain the Other contain the acetylideacetylide ion (Cion (C2222--) and give ) and give ethyneethyne..

Structure of CaCStructure of CaC22 is similar to is similar to NaClNaCl structure with Cstructure with C2222-- ions arranged in a parallel ions arranged in a parallel

fashion.fashion.

CaCCaC22 + 2H+ 2H22O O �������� CC22HH22 + Ca(OH)+ Ca(OH)22

LiLi44CC33 + 4H+ 4H22O O �������� MeC≡CHMeC≡CH + 4LiOH+ 4LiOH

OxidesOxides

The oxides of carbon, being gases, are quite different from those of the The oxides of carbon, being gases, are quite different from those of the other Group 14 elements.other Group 14 elements.

Structural difference results from the presence of strong pStructural difference results from the presence of strong pππ--ppππ bonding bonding between carbon and oxygen.between carbon and oxygen.

Carbon oxides are discrete species.Carbon oxides are discrete species.

In contrast, for silicon the Si=O bond is unstable with respect to two SiIn contrast, for silicon the Si=O bond is unstable with respect to two Si--O O single bonds, and so silicon oxides and many single bonds, and so silicon oxides and many oxyanionsoxyanions have infinite, have infinite, covalent network structures of Sicovalent network structures of Si--O bonds.O bonds.covalent network structures of Sicovalent network structures of Si--O bonds.O bonds.

Heating the element in oxygen produces the dioxide, EOHeating the element in oxygen produces the dioxide, EO22..

CO, COCO, CO22, C, C33OO22

HCOOH HCOOH �������� CO + HCO + H22O (dehydration of formic acid with conc. HO (dehydration of formic acid with conc. H22SOSO44))

CO is poorly soluble in water and does not react with it.CO is poorly soluble in water and does not react with it.

CO + OH CO + OH �������� HCOHCO22-- ((formateformate anion) (with concentrated hydroxide)anion) (with concentrated hydroxide)

CO is isoelectronic with NCO is isoelectronic with N22 and has similar physical properties.and has similar physical properties.

CO is very poisonous and much more reactive than nitrogen.CO is very poisonous and much more reactive than nitrogen.

It combines with the halogens (except iodine) directly, for example with chlorine to It combines with the halogens (except iodine) directly, for example with chlorine to give the highly poisonous phosgene gas.give the highly poisonous phosgene gas.

CO +ClCO +Cl2 2 �������� COClCOCl22CO is an excellent ligand in coordination chemistry of transition metals.

Ni(CO)Ni(CO)44, Cr(CO), Cr(CO)66, Ru, Ru33(CO)(CO)1212, Ir, Ir44(CO)(CO)1212 etc.

CO compares well with PRCO compares well with PR33 in its donorin its donor--acceptor properties.acceptor properties.

COCO22 is the most stable oxide produced on an enormous scale industrially by is the most stable oxide produced on an enormous scale industrially by COCO22 is the most stable oxide produced on an enormous scale industrially by is the most stable oxide produced on an enormous scale industrially by the combustion of coal, oil and natural gas.the combustion of coal, oil and natural gas.

In laboratory, CaCOCaCO33 �������� CaOCaO + CO+ CO22

COCO22 is soluble in water, mostly as dissolved COis soluble in water, mostly as dissolved CO22 molecules but a small molecules but a small amount of COamount of CO22 is hydrated to give carbonic acid, His hydrated to give carbonic acid, H22COCO33..

This is a weak acid, partly dissociates to This is a weak acid, partly dissociates to hydrogencarbonatehydrogencarbonate (HCO(HCO33--) or CO) or CO33

22--

ions.ions.

2NaO + CO2NaO + CO22 �������� NaNa22COCO33; 2OH2OH-- + CO+ CO22 �������� COCO3322-- + H+ H22OO

CaCO3(s) + CO2(g) + H2O (l) Ca(HCO3)2 (aq)

This equilibrium is very important in geochemistry, for example the This equilibrium is very important in geochemistry, for example the deposition and redissolution of limestone rock during weathering.deposition and redissolution of limestone rock during weathering.

CH2(COOH)2-2H2O

P4O10O C C C O

The structural chemistry of SiOThe structural chemistry of SiO22 is extremely complex; the stable form is extremely complex; the stable form The structural chemistry of SiOThe structural chemistry of SiO22 is extremely complex; the stable form is extremely complex; the stable form

of of SiOSiO under ambient conditions is quartz, and other highunder ambient conditions is quartz, and other high--temperature temperature

((tridymitetridymite and and cristobalitecristobalite) modifications are known.) modifications are known.

The different ways of linkages shown by SiOThe different ways of linkages shown by SiO44 tetrahedratetrahedra results in results in various SiOvarious SiO22 structures.structures.

A vast number of polymeric silicates occur naturally.A vast number of polymeric silicates occur naturally.

More details on polymeric silicates will be given while discussing selected polymeric Main Group compoundsMore details on polymeric silicates will be given while discussing selected polymeric Main Group compounds

GeOGeO22, SnO, SnO22 and PbOand PbO2 2 have considerable ionic character and have considerable ionic character and adopt rutile (TiOadopt rutile (TiO22) structure) structure

Ge, Sn, Pb

O

six coordinated metal and three coordinated oxygensix coordinated metal and three coordinated oxygen

These oxides are amphoteric, and dissolve in both acids and bases.These oxides are amphoteric, and dissolve in both acids and bases.

The hydrated SnThe hydrated Sn2+2+ and Pband Pb2+2+ ions undergo substantial hydrolysisions undergo substantial hydrolysis

CSCS22 is a molecular substance similar to COis a molecular substance similar to CO22..

The species, CS, sulfur analogue of CO is unstable as a free The species, CS, sulfur analogue of CO is unstable as a free moleulemoleule, but can be , but can be stabilized by coordination to a metal.stabilized by coordination to a metal.

Several transition metalSeveral transition metal--CS complexes are known.CS complexes are known.

[[RhClRhCl(CS)(PPh(CS)(PPh33))22

The compounds ME and METhe compounds ME and ME22 (E = S, Se, Te) are known for (E = S, Se, Te) are known for GeGe, , SnSn and and PbPb..

Polyatomic Anions of the Group 14 ElementsPolyatomic Anions of the Group 14 Elements

When alloys of heavy Group 14 elements (When alloys of heavy Group 14 elements (GeGe, , SnSn, , PbPb) and alkali ) and alkali metals are dissolved in liquid ammonia or en, polyatomic anions are metals are dissolved in liquid ammonia or en, polyatomic anions are produced.produced.

These can be crystallized if a donor These can be crystallized if a donor ligandligand, such as a crown ether is , such as a crown ether is

added to the solution to complex the alkali metal added to the solution to complex the alkali metal cationcation..

Known Known polyanionspolyanions are Snare Sn4422--, Ge, Ge44

22--(tetrahedral), Sn(tetrahedral), Sn5522--, Pb, Pb55

22-- (TBP), (TBP), and Snand Sn99

22-- (predict the structure using Wade’s rules).(predict the structure using Wade’s rules).

CS is not stable above CS is not stable above --160 160 ooCC, many MCS compounds can be made, many MCS compounds can be made

M C S

M C S M

C

M

M

MC

M M MM

SC

M

SS

Linear CS is a better Linear CS is a better σσσσσσσσ--donor and donor and ππππππππ--acceptor than CO, but depends on acceptor than CO, but depends on electron richness of the metalelectron richness of the metal

Very few Very few homoleptichomoleptic thiocarbonylthiocarbonyl complexes are known. Ni(CS)complexes are known. Ni(CS)44 is is unstable at room temp.unstable at room temp.Many mixedMany mixed--ligandligand complexes are known with properties similar to complexes are known with properties similar to those of pure carbonyl complexes.those of pure carbonyl complexes.

Cr(CO)Cr(CO)55(CS), ((CS), (ηηηηηηηη66--CC66HH66)Cr(CO))Cr(CO)22(CS), Cr(CO)(CS), Cr(CO)33(CS){P((CS){P(OPhOPh))33}}22, Fe(CO), Fe(CO)44(CS) (CS)

Mn

OC COL

CS2

-LMn

OC

OC

CS

S

PR3

- S=PR3

Mn

OCCS

CO

{Fe(CO)4]2- CSCl2

{Fe(CO)4(CS)]

RhCl(PPh3)3 + CS2 trans-RhCl(CS)(PPh3)2 + S=PPh3RhCl(PPh3)3 + CS2 trans-RhCl(CS)(PPh3)2 + S=PPh3

(Me3P)2(CO)2Fe(ηηηη2-CS2Me)

Na/Hg Fe(CS)(CO)2(Me3P)2

Free CS, Free CS, ννννννννCS , 1273 cmCS , 1273 cm--11

MM33((µµµµµµµµ33--CS), 1040CS), 1040--1080 cm1080 cm--11

MM22((µµµµµµµµ--CS), 1100CS), 1100--1160 cm1160 cm--11

MM--CS, 1160CS, 1160--1410 cm1410 cm--11

Group 15 (Group 15 (PnictogenPnictogen) Elements: N, P, As, ) Elements: N, P, As, SbSb and Biand BiGroup 15 (Group 15 (PnictogenPnictogen) Elements: N, P, As, ) Elements: N, P, As, SbSb and Biand Bi

••OxidationOxidation statesstates ofof ++33 andand ++55 occuroccur forfor allall elementselements

•• ++33 statestate isis mostmost stablestable forfor bismuthbismuth duedue toto inertinert pairpair effecteffect

••++55 isis stablestable forfor phosphorus,phosphorus, butbut actsacts asas anan oxidizingoxidizing agentagentwithwith nitrogen,nitrogen, arsenicarsenic andand antimonyantimony..

••ArsenicArsenic withwith completelycompletely filledfilled 33dd innerinner shellshell whichwhich isisrelativelyrelatively poorlypoorly shielding,shielding, isis ratherrather moremore difficultdifficult toto oxidizeoxidizerelativelyrelatively poorlypoorly shielding,shielding, isis ratherrather moremore difficultdifficult toto oxidizeoxidizetoto thethe ++55 statestate duedue toto addedadded inertinert pairpair effecteffect..

••TheThe --33 oxidationoxidation statestate occursoccurs inin thethe hydrideshydrides suchsuch asas NHNH33,,andand inin anionsanions suchsuch asas PP33-- (Na(Na33P)P)..

N

N

N

N

N N

N

N

N

N

N

N

N

Azidopentazole

N N

NN55++

BecauseBecause NN22 isis aa veryvery stablestable molecule,molecule,bothboth thermodynamicallythermodynamically andand kinetically,kinetically,otherother speciesspecies comprisedcomprised ofof nitrogennitrogenatomsatoms areare rarerare.. **NN55

++ waswas isolatedisolated inin19991999.. TheThe authorsauthors ofof thethe viewview thatthat highhighenergyenergy ionicionic allotropeallotrope ofof nitrogennitrogen NN55

++NN33--

maymay bebe isolatedisolated..AnotherAnother nitrogennitrogen compoundcompound isis NN88..

*K*K..OO.. ChristeChriste,, WW..WW.. Wilson,Wilson, JJ..AA..SheehySheehy andandJJ.. AA.. BoatzBoatz,, AngewAngew.. ChemChem.. IntInt.. EdEd.. EnglEngl..19991999,, 3838,, 20042004..

Azidopentazole

HighHigh energyenergy--densitydensity materialsmaterials.. ScopeScopeofof makingmaking manymany otherother homoatomichomoatomicnitrogennitrogen speciesspecies..

InIn covalentcovalent azidesazides,, thethe NN33 groupgroupbehavesbehaves asas aa pseudohalogenpseudohalogen,, sosothatthat thethe moleculesmolecules (N(N33))22 andandN(NN(N33))33 areare alsoalso potentialpotential nitrogennitrogenallotropes,allotropes, analogousanalogous toto ClCl22 andandNClNCl33,, respectivelyrespectively..

Some important Some important pseudohalidespseudohalides

AzideAzide NN33--

CyanideCyanide CNCN--

CyanateCyanate NCONCO--

ThiocyanateThiocyanate NCSNCS--

Behavior is similar to halide ionsBehavior is similar to halide ions

••The principle source of phosphorus is phosphate rock, a complex The principle source of phosphorus is phosphate rock, a complex calcium phosphate.calcium phosphate.

••Reduction of phosphate rock gives white phosphorus, with a Reduction of phosphate rock gives white phosphorus, with a tetrahedral structure which persists in solid, liquid and gaseous tetrahedral structure which persists in solid, liquid and gaseous state.state.

••When PWhen P44 vapourvapour is heated to 800 is heated to 800 ooCC, appreciable amount of triply , appreciable amount of triply bonded Pbonded P22 molecules are formed. molecules are formed.

••Prolonged heating of white phosphorus in a sealed vessel results Prolonged heating of white phosphorus in a sealed vessel results ••Prolonged heating of white phosphorus in a sealed vessel results Prolonged heating of white phosphorus in a sealed vessel results in the formation of red phosphorus, a relatively inert form of the in the formation of red phosphorus, a relatively inert form of the element, with a poorly defined but complex structure.element, with a poorly defined but complex structure.

••However, the most stable allotrope is black phosphorus, formed by However, the most stable allotrope is black phosphorus, formed by heating phosphorus at high pressure, which has several structures; heating phosphorus at high pressure, which has several structures; the the rhombohedralrhombohedral form has a layer structure. form has a layer structure.

Arsenic, antimony and bismuth occur predominantly as sulfides. These Arsenic, antimony and bismuth occur predominantly as sulfides. These three elements form layered structures related to black phosphorusthree elements form layered structures related to black phosphorus

P

P

P

P

white phosphorus

P

P

P

P

P

P

P

P

P

P

P

P

P

P

P

P

nred phosphorus

P

P

P

P

P

P

P

P

P

P

P

P

P

P

P

P

n

P

P

P

P

2n

sublimation

The structure of rhombohedral black phosphorus

HydridesHydrides

All five Group 15 elements form hydrides EHAll five Group 15 elements form hydrides EH33, but with different trend in their , but with different trend in their physical and the chemical properties.physical and the chemical properties.

Boiling points increase on going town the group, with the exception of the Boiling points increase on going town the group, with the exception of the anomalously high boiling point of NHanomalously high boiling point of NH33, which is due H, which is due H——NN--H hydrogen H hydrogen bonding.bonding.

The HThe H--EE--H bond angles also decrease going down the group, owing to the H bond angles also decrease going down the group, owing to the decreasing Edecreasing E--H bond strengths.H bond strengths.

Thermal stabilities decrease down the group.Thermal stabilities decrease down the group.

Enthalpies of formation parallel the E-H bond energies for these compounds.

∆∆∆∆∆∆∆∆ffHHoo (kJ mol(kJ mol--11)) EE--H bond energy (kJ molH bond energy (kJ mol--11))

NHNH33 --46.246.2 +391+391

PHPH33 +9.3+9.3 +322+322

AsHAsH33 +172.2+172.2 +247+247

SbHSbH33 +142.8+142.8 +255+255

EE--EE single,single, doubledoubleandand tripletriple bondbondenergiesenergies forfor nitrogennitrogenandand phosphorusphosphorusBondBond BondBond energyenergy

(kJ(kJ molmol--11))NN−−−−−−−−NN ++160160PP--PP ++200200NN==NN ++419419P=PP=P ++310310N≡NN≡N ++945945P≡PP≡P ++490490

Single,Single, doubledouble andand tripletriple bondbond strengthsstrengths forfor NN--NN andand PP--PP bondsbondsareare givengiven.. ShowShow thatthat thesethese areare consistentconsistent withwith thethe occurrenceoccurrence ofofnitrogennitrogen asas solelysolely aa tripletriple bondedbonded diatmoicdiatmoic moleculemolecule..

TheThe N≡NN≡N tripletriple bondbond energyenergy isis moremore thanthan threethree timestimes thatthat ofofthethe singlesingle NN--NN bondbond energy,energy, soso NN--NN singlesingle bondedbonded allotropesallotropesareare unstableunstable relativerelative toto NN22.. TheThe N≡NN≡N bondbond energyenergy isis alsoalsogreatergreater thanthan thethe sumsum ofof thethe N=NN=N andand NN--NN energiesenergies (in(in aa ––N=NN=N--

N=NN=N-- form),form), soso thisthis isis alsoalso unfavorableunfavorable relativerelative toto thethe N≡NN≡N..

Rationalize the trend in the HRationalize the trend in the H--EE--H bond angles in H bond angles in the series of hydridesthe series of hydrides

Molecule NHNH33 PHPH33 AsHAsH SbHSbH33

H-E-H bond angle (o) 107 93.5 92 91.5

All have tetrahedral arrangement (3BP +1LP); angles are expected to be <109.5o

Owing to the effect of the lone pair.

Distortions to the basic shape is due to the difference in electronic distribution in the E-H bonds. The N-H bond short (101.5 pm) and the nitrogen is more electronegative than hydrogen, so the bonding pair will reside close to the central N atom, occupying more space in its valence shell. These N-H bonding pairs will repel each other more, widening the bond angle.

N

H H

H

Sb

H H

H

NHNH33 manufacturing:manufacturing:

NN22 + 3H+ 3H22 �������� 2NH2NH33 [ high pressure and temp, catalyst)[ high pressure and temp, catalyst)

Liquid ammonia (B.P. Liquid ammonia (B.P. --33 33 ooCC) has comparisons with water as a solvent; ) has comparisons with water as a solvent; HH33OO

++ and OHand OH-- are respectively an acid and a base (a proton acceptor) in are respectively an acid and a base (a proton acceptor) in water, while in ammonia, NHwater, while in ammonia, NH ++ is an acid and NHis an acid and NH ++ is a base.is a base.water, while in ammonia, NHwater, while in ammonia, NH44

++ is an acid and NHis an acid and NH22++ is a base.is a base.

Phosphine, PHPhosphine, PH33

2P2P44 + 12H+ 12H22O O �������� 5PH5PH33 + 3H+ 3H33POPO44

Ultrapure PHUltrapure PH33: (thermal disproportionation of phosphorus acid (H: (thermal disproportionation of phosphorus acid (H33POPO33))

4H4H33POPO33 �������� PHPH33 + 3H+ 3H33POPO44

4EX4EX33 + 3Li[AlH+ 3Li[AlH44] ] �������� 4EH4EH33 + 3Li[AlX+ 3Li[AlX44]]

Hydrolysis of metal phosphide:Hydrolysis of metal phosphide: CaCa33PP22 + 6H+ 6H22O O �������� 2PH2PH33 + 3Ca(OH)+ 3Ca(OH)22