sign in sign up
<<
Home , Crystal Field Theory, Ligand, Metal carbonyl, Mond process

CHAPTER 11 Metal-II Complexes: •!• Metal Carbonyls: Structure and Bonding

The bonding in coordination compounds is usually visualized as the donation of electron pair to the metal centre only. However, there are some which not only have filled atomic orbitals (donor orbitals) but also have some empty orbitals (acceptor orbitals) of appropriate symmetry and energy to accept electron density from central metal atom or . This interaction is called n:-backbonding or n:-backdonation; and is generally shown by CO, NO, PR3 and - type li gands. Two of the most common examples where n:-backbonding occurs include Ni(C0)4 and Zeise's salt. Furthermore, metal carbonyls are one of the most widely studied type of metal-n: complexes, that can simply be defined as the coordination compounds of transition metals with monoxide as a ligand. Metal carbonyls are very useful in synthetic organic and in , like the process of . In the , carbonyl is used to produce pure nickel. In , metal carbonyls act as precursors for the synthesis of many organometalic compounds. Metal carbonyls are toxic by inhalation, skin contact, or ingestion, in partially due of their ability to attach to of to give , which inhibits the binding of dioxygen. Metal carbonyls can be classified on the basis of number of metal centres; mononuclear carbonyls have only one metal atom or ion such as Fe(CO)s, while polynuclear carbonyls contain more than one metal centre like homonuclear Fe2(C0)9 and heteronuclear MnRe(C0)10. One more categorization basis of metal carbonyls is the bonding profile of carbonyl li gand; non-bridging carbonyls and bridging carbonyls. Non-bridging carbonyls may or may not contain metal-metal bond. For instance, Ru(CO)s and Mn2(C0)10 both have only terminal carbonyl groups but

Mn2(C0)1o has one metal-metal bond also. On the other hand, bridging metal carbonyls like Fe3(C0)12, in addition to terminal CO groups, do have CO groups bridged to more than one metal centres.

~ General Methods ofPreparation

1. By direct reaction: Some of the mononuclear carbonyls can be prepared by the direct reaction of with metal powder.

2s 0 c Ni + 4CO -----+ Ni(C0)4 1 atm 200°c Fe+ SCO ------+ Fe(C0)5 200 atm 1so 0 c 2Co + 8CO ------+ Co 2 (C0)8 35 atm

DALAL D INSTITUTE CHAPTER 11 Metal-n Complexes: 427

2. By reduction: One of the most widely used method to synthesize metal carbonyls is the reduction of corresponding metal salts in the presence of carbon monoxide.

AICl 3 CrCl3 +Al + 6CO ------+ Cr(C0)6 + AICl 3 diglyme, 100°c VCl 3 + 4Na + 6CO ------+ [(diglyme) 2 Na] [V(C0) 6] + 3NaCI high pressure

200°c 2COl 2 + 4Cu + sco-----~ Co 2 (C0)8 + 4Cul 200 atm 120 - 200°c 2CoC0 3 + 2H 2 + SCO ------+ Co2 (C0)8 + 2H 2 0 + 2C02 250 - 300 atm 250°C

350 atm

In the last reaction, carbon monoxide is the on its own. 3. From mononuclear carbonyls: is sensitive to light and air and can be used to synthesize Fe2(C0)9 by direct photolysis.

hv 2Fe(C0)5 Fe2 (C0)9 +CO

Similarly

hv 20s(C0)5 Os 2 (C0)9 +CO hv 2Ru(C0)5 Ru 2 (C0)9 + CO

4. From iron pentacarbonyl: Carbon monoxide ligands in Fe(CO)s are labile and therefore can be used synthesize other metal carbonyls.

110°c MoC1 6 + 3Fe(C0)5 ------+ Mo(C0)6 + 3FeCl2 + 9CO ether 110°c WCl 6 + 3Fe(C0)5 ------+ W(C0)6 + 3FeCl2 + 9CO ether

5. From metathesis reaction: Mixed-metal carbonyls can successfully be prepared via metathesis reaction route as:

KCo(C0) 4 + [Ru(C0)3 Cl2 ]z ------+ 2RuCo2 (C0)11 + 4KCI DALAL D INSTITUTE 428 A Textbook of - Volume I

~ Structures ofMetal Carbonyls

The structure of metal carbonyls can mainly be classified into three categories; first as the mononuclear systems that contain only one metal atom, the second one as binuclear systems that may or may not contain bridging carbonyls, and the last one as the polynuclear systems which contain more than two metal centres with all terminal, all bridging, or a mixture of two types of carbonyl groups. 1. Mononuclear metal carbonyls: The structure of mononuclear metal carbonyls is pretty simple and easy to visualize. This is definitely due to the presence of only one metal centre. The general examples of mononuclear metal carbonyls include tetrahedral Ni(C0)4 and Pd(C0)4; the trigonal bipyramidal case ofFe(CO)s, Ru(CO)s and Os(CO)s; and the octahedral geometries of V(C0)6, Cr(C0)6, Mo(CO)s and W(C0)6.

co co

I \\\\111CO oc ,,,,, I 11\\\CO oc--M·"' '''• .. M ..,, ,\ 1~co ocfll"""' I ""co co co

M(C0)4 M(C0)5 M(C0)6 M - Ni, Pd M - l't:, Ru, Os M - V, Cr, Mo, W

Figure 1. The structures of some mononuclear metal carbonyls.

2. Binuclear metal carbonyls: The structure of the binuclear metal carbonyls comprises of two metal centres and involve either metal-metal bonds or bridging CO groups, or both. For example, the Co2(C0)8 is known to exist in two . The first one of has a D 3d symmetry with one metal-metal bond with zero bridging carbonyl; the second one is of C2v symmetry and has two bridging CO ligands along with one metal-metal bond. The structure of Fe2(C0)9 exist with D Jh symmetry, and contains three bridging CO ligands and six terminal CO groups attached. Furthermore, M2C010 (M =Mn, Tc, Re) exists with D 4d symmehy with one metal-metal bond and four CO ligands attached to each of the metal centre.

c0 ~o ~~ co oc ~ ~ ~o~ I \ ! oc"' .f; c ~.. /co oc--co----c0 --co .Co Co '!<.,,, •••, \'•,,,,, 0 I \ I oc~ co oc t~ o co oc co

Co2(C0)8

Figure 2. continued on next page ... DALAL D INSTITUTE CHAPTER 11 Metal-n Complexes: 429

c0 oc co oc ~~ co lo I co ~:::-o~ / \.:~ ~! ..~ c~.. OC --M -----M--CO .Fe Fe. oc''/ ""c/ \'11co I\ /I oc 0 co oc co oc co

M 2(C0)10 M - Mn, Tc, Re

Figure 2. The structures of some binuclear metal carbonyls.

3. Polynuclear metal carbonyls: The structures of the polynuclear metal carbonyls comprises of three or more metal centres and involve all bridging, all terminal, or a mixture of two types of CO groups. For example, the Ru3(C0)12 cluster has D3h symmetry, comprises of an equilateral triangle of Ru centres, each of which has two axial and two equatorial CO ligands. Os3(C0)12 has the same structure, whereas Fe3(C0)12 is different, with two bridging CO ligands, resulting in C2v symmetry. M4C012 (M =Co, Rh) is consisted of a tetrahedral M4 core, but the is C3v· Three carbonyl ligands are bridging ligands and nine are terminal. However, lr4(C0)12 has perfect Td symmetry with no bridging CO ligands groups. The Rh4 and Jr4 clusters are more thermally robust than that of the Co4 compound, reflecting the usual trend in the strengths of metal-metal bond for second and third row metals vs those for the first row metals. Furthermore, [Re4(C0)16]2- has D2h symmetry with no bridging carbonyl. Furthermore, the structure of Os4(C0)16, Os4(C0)1s and Os4(C0)14 are somewhat more complex because of non-rigidity. The tetranuclear Os4(C0)16 is analogues to the cyclobutane with a puckered structure. The X-ray diffraction analysis of Os4(C0)14 unveiled an irregular tetrahedral Os4 skeleton with four weakly semi-bridging CO groups and four different Os-Os bond lengths. The experimental structure of Os4(C0)1s was determined to have a planar butterfly-like geometry consisting of two triangles sharing an edge. The hexanuclear M6(C0)16 (M = Rh, Co) exists with an octahedral core with alternate faces participating in the bridging; i.e. with four triply bridged and twelve terminal carbonyls.

0 ;::,c~ oc ~tg~/co

oc'''''7 _.. Fe~ l/Fe\'''''''''''co /~e'-. \ oc oc ~ co co co M3(C0)12 M = Os, Ru Fe3(C0)12

Figure 3. continued on next page ...

DALAL D INSTITUTE 430 A Textbook of Inorganic Chemistry - Volume I

co oc, I ,...... co M

oc ' / /';___ __ .-8 .. / co 'r.,1- -• -• -• - ~•.•• M oc /'.~Le\ ,' :"' co OC------M ------CO I\ oc co

M4(C0)12 M - Co,Rh

co oc co oc'%.. / co \r _os ~OC1111,,. I ,,,,,,,co -----=:;;:::='Os ""'CO oc"'j """ ~·os·?--- ~ \ oc I I co Os CO oc,.- I ~co co

co

OC11,,,, I ,,,,,co co ''•·. - ···'' co ,,,,,,,,,,,, 01s ,,,,,,,,,,,,,,, I ~co I ,,,,,,\ ,,,,,,,, ....~ oc -T~ Co r /f--co co ~otl"' co oc,,,, I ' co co

Figure 3. continued on next page ... DALAL D INSTITUTE CHAPTER 11 Metal-n Complexes: 431

oc~ /co

OC' -- ,.M\,'· ·- , , ··~:c;o '" , ' I', ,' I f \. , I ' ' ,. \ I \. , t I '\ -., " 1 OC ··~" , OC- -M- -:..--c ',, ""M :' ~"-:-',/ / ---.....__~·/ '\ \ _..,,..co / .. ~ ". --- ~1 ...... oc ""'·~r-:-,-::-ko ~- - /':' ...... co DALAL INSTITUTI~/.." ...~·/::c~· Main Market, Sector-14, Rohtak, Haryana /M...... ___ www.dalalinstitute.com, +91-9802825820 oc co NET.JRF, Ill-GATE, Ill.JAM & M.Sc Entrance (Chemistry) tvii;(CO) i6 M = Co,Rh

Figure 3. The structures of some polynuclear metal carbonyls.

~ Bonding in Metal Carbonyls

In order to rationalize the nature of the bonding between metal centre and the carbonyl ligand, we must understand the bonding within the carbonyl ligand itself first. It is a quite well known fact that CO group acts as a good sigma donor as well as good n-acceptor ligand. Two popular approach to study the bonding in carbon monoxide as well as metal carbonyls are discussed below. 1. Valence bond theory: According to this model, the bonding within the CO can be best shown as: o=:tc

The carbon and atom in carbon monoxide are sp-hybridized with following electronic configurations.

2 1 0 C (hybridized state)= l s2, (spx) , (spxY , 2py , 2pz

Similarly,

2 2 1 0 (hybridized state) = ls , (spx) , (spx) , 2py1, 2p/

DALAL D INSTITUTE 432 A Textbook of Inorganic Chemistry - Volume I

Now, the one half-filled spx-hybridized orbital of carbon atom overlap with half-filled spx-hybridized orbital of the oxygen atom to form a cr bond, while spx-hybridized lone pairs on both atoms remain non-bonding in nature. Moreover, two 7t bonds are formed as a result of the sidewise overlap; one between half-filled 2py orbitals, and the second one as a dative or coordinative interaction of fully filled 2pz orbital of oxygen with empty 2pz orbital of carbon.

t , " ' -', 2n'r: I , ' ' ,' ' , ' ,'

,,,""' ,' , ' ' ,' '' ' -- ',_, '

Car b on - spx 2 , spx 1, 2120Py , .P= Oxygen = sp_}, sp}, 2p:}, 2p}

t ,-, ,,' , / / ' Main Market, Sector-14, Rohtak, Haryana

, ' www.dalalinstitute.com, +91-9802825820 / ' , ' ' NET.JRF, UT-GATE, Ill.JAM & M.Sc Entrance : , .-.--+--+---+-,,_. (Chemistry)

Carbonyl Group

Figure 4. Bonding behaviour in CO ligand according to valence bond method.

Furthermore, the valence bond theory treats the bonding mode of carbonyl with metal centre in tenns of hybridization and the phenomena. The central metal atom or ion provides the required number of empty hybrid orbitals with proper orientation to accept the electron pair from surrounding ligands. For instance, in Cr( Co )6 the atom undergoes a dsp2 hybridization to generate six empty hybrid orbital equivalent shape and same energy. When one of the carbonyl ligand approaches this metal ion with its internuclear axis along x-axis, the filled hybrid of electron on carbon atom overlap with one of the two empty hybrid orbital orientated oppositely in x-direction. The metal-carbon multiple bond is explained in terms of various resonating structures which consequently reduces the bond strength of carbon-oxygen bond. It should also be noted that, though there are two hybrid lone pairs (one on carbon and the other on the oxygen); the bonding of with metal takes place via donation though carbon end always. This can be explained in terms of higher energy of hybrid lone pair carbon then oxygen.

DALAL D INSTITUTE CHAPTER 11 Metal-n Complexes: 433

M --C--0

Metal-Carbonyl cr bonding Q'' "''""""'''9 -o 0

M--c ---o 1vr==== C---O

Metal-Carbonyl 7t bonding

Figure 5. The valence bond nature of a and n overlap in metal carbonyls.

2. theory: This is the best model to explain the bonding within the CO ligand as well as in complexes. There are total three molecular diagram for carbonyl ligand which were proposed from time to time. Though, all the three molecular orbital (MO) diagrams are able to explain the nature of metal-carbonyl n-bonding; the initial treatment was not so effective to explain the a donation, the second one does also suffer from some minor anomalies. The third molecular orbital diagram is most widely accepted in the scientific community as it gives logical explanation to what had been a mystery in metal carbonyl chemistry. We will study these MO diagrams in the order they were proposed. i) The first molecular orbital diagram of carbon monoxide assume that the atomic orbitals of carbon and oxygen interact with each other to create molecular orbitals. The electronic configurations of C and 0 are:

The number of outer electrons in carbon and oxygen are four and six, respectively. Thus, a total of I 0 electrons are to be filled in the molecular orbitals of carbon monoxide molecule. The higher energy of c01Tesponding atomic orbitals of carbon is due to its lower electronegativity, which makes the bonding and antibonding molecular orbitals to receive different contributions from atomic orbitals of carbon and oxygen. The bonding molecular orbitals will be rich in atomic orbitals of oxygen while antibonding molecular orbitals, that are closer to carbon in energy, would be rich in atomic orbitals of carbon. The bonding molecular orbitals will have more characteristics of atomic orbitals of Oxygen and antibonding Molecular orbitals would have more

DALAL D INSTITUTE 434 A Textbook of Inorganic Chemistry - Volume I

2 2 characteristics of carbon. The electronic configuration of CO molecule will be cr2s , cr*2s , cr2pz2, 1t2pl, 1t2p/ which gives a bond order three i.e. triple bond between carbon and oxygen. The molecular orbital diagram and expected bonding mode of the carbonyl ligand are given below.

, , ' ' , ' ' , . , ' ' ------.. ' ' ----* * ._ .'\ 7t 2px 1t 2py ',, \ ' ' '' ' '' "\

DALAL INST1IT'Ulf£, Main Market, Sector-14, Rohtak, Haryana www.dalalinstitute.com, +91-9802825820 , ' ' ' a *2s ' NET-JRF, Ill-GATE, llT-JAM & M.Sc Entrance ' ' - ' u - ' (Chemistry) ' 2 ' ' 2s ' ' ' ' ' ' ' ' ' ' ' ' ' . ' 2s2 ' ' a2s

c co 0

Figure 6. The first generation molecular orbital diagram of carbonyl ligand.

The formation of molecular orbitals given above is actually an oversimplification of a ticklish problem. This statement is made on the basis of two facts. The first one is that when one electron removed from co to form co+, the bond order actually increases, which is actually opposite of what is expected if electron is lost from a highest occupied molecular orbital (HOMO) of bonding nature. Its bond order should be decreased from the removal of electron from 1t2pl or 7t2p/ , which suggest that the HOMO of carbon monoxide should be of antibonding nature rather bonding. The second anomaly also arises from the MO diagram of CO ligand which clearly shows that in order to donate electron density from 7t-bonding molecular orbital, the carbonyl ligand must approach the metal centre with its carbon-oxygen internuclear axis perpendicular to x, y or z-axis assigned to central atom. This explains how the empty 1t*2px and 1t*2py could be used to accept electron density from filled d-orbitals of central metal atom or ion. However, in actual practice, the carbonyl ligand binds to metal centre in linear fashion via carbon end only.

DALAL D INSTITUTE CHAPTER 11 Metal-n Complexes: 435

M..,..,../0___ , ~c

Metal-Carbonyl cr donation and 7t acceptance

Figure 7. The expected nature of a and n overlap in metal carbonyls from first MO of CO.

ii) The second molecular orbital diagram of carbon monoxide was suggested by Coulson which assumes that the first molecular orbital diagram of CO is not correct. According to Coulson, 2s and 2px atomic orbitals of both carbon and oxygen undergo hybridization before they create molecular orbitals. The carbon and oxygen atom in carbon monoxide are sp-hybridized with following electronic configurations.

2 2 1 0 C (hybridized state) = l s , (spx) , (spx)1, 2py , 2pz

2 2 1 0 (hybridized state) = ls , (spx) , (spx)1, 2py , 2p/

The total number of valence electrons in carbon and oxygen are four and six, respectively; and thus, ten electrons are to be filled in the molecular orbitals of CO molecule. The half-filled spx hybrid orbitals of carbon and oxygen interact to form a and a· molecular orbitals; while the fully-filled spx hybrid lone pair orbitals of carbon and oxygen remains non-bonding. Moreover, doubly degenerate sets of n-bonding and n-antibonding molecular orbitals are also fo1med due to the sidewise overlap of 2py orbitals and 2p, orbitals.

t l .. ,, , .,,' 2p= '

') SP.x - ...._t~·~~'\'-=::::::__!_t_.., er and er* , , ' :,pxl '..' -.. , -- rr2p= and rr*2p=

- 2 1 2 1 ,0 - 2 1 212 2 Cbar on - spx , spx , Py , ~P= 0 xygen - spx , spx , Py , P:

Figure 8. The nature of a and 7t in carbonyl ligand.

The bonding molecular orbitals will be rich in atomic orbitals of oxygen while antibonding molecular orbitals, that are closer to carbon in energy, would be rich in atomic orbitals of carbon. The bonding molecular orbitals DALAL Copyright © Mti.-n~e.e.? Pti.-ltll D INSTITUTE 436 A Textbook of Inorg anic Chemistry - Volume I will have more characteristics of atomic orbitals of oxygen and antibonding molecular orbitals would have more characteristics of carbon. The molecular orbital diagram carbon monoxide proposed by Coulson is given below.

,' cr . . ' . ' . ' ~- - ~ \ t tt t .. .. ., "'/ rr,*?p rr.*2p \ \ ---.i ------.-, ,' - x Y \\ \ .. ~ ' ' . 2 I 2 0, , '• -Px') 1 , 2P y,1 2P: 0 \ '.. J~v ' .JJ: \ ,' \ · \' .. , \ ,' ' ".. ' , :>--t~•---- \; ------__.t...... +_ ',:\ 2 \: (spx) :' \ nb(C) \\ , . ' ' \ :' " t :' '. \\ t t+ t t tt ' H .:> ,_(s-p-x)-1--<\ '\ >,>--2 -1-2 - 2 - - - - ~---: 2 I 2 I 2 2 ---- \ ' \ . , ,- \ Pv , P: ,,-' :' Px , Py, P: 2 \ 2s . ' ' ' - '. ' , f ' ,' ' , .. ' \ \.ti_ JL,·' , I ' . ' rr.2px rr.2py . ' . ' . . .' ' ,' '. ' ..I ' \ .' D:ALAl INSTITUTE " Main Market, Sector-14, Rohtak, Haryana .' (j '•'. www.dalalinstitute.com, +91 -9802825820 ' ' I ' ,' ~ NET.JRF, llT·GATE, llT.JAM & M.Sc Entrance ' . (Chemistry) .' '.

nh(O)

2s2

Carbon co Oxygen

Figure 9. The second molecular orbital diagram of carbonyl ligand.

The MO diagram shown above is very useful in explaining the bonding between metal centre and carbonyl ligand. This diagram eliminates the possibility of sigma donation through bonding molecular orbital and perpendicular orientation CO ligand as the HOMO is now non-bonding hybrid lone pair rather n-bonding. This also explains why the carbonyl group prefers to bond via carbon end in linear manner. This also explains how the lowest unoccupied molecular orbital (LUMO) n*2px and n*2py could be used to accept electron density from filled d-orbitals of central metal atom or ion. Moreover, the reduced CO stretching frequency of metal coordinated carbonyl can be attributed to the reduced bond order due to transfer of d-electron density from metal ton· orbital carbonyl ligand. However, the increase in bond order when one electron is removed from

DALAL D INSTITUTE CHAPTER 11 Metal-n Complexes: 437

CO to form co+i s still a mystery because the electron is lost from a highest occupied molecular orbital (HOMO) ofnonbonding bonding nature, and the bond order should have been decreased.

Figure 10. The nature of a and rc overlap in metal carbonyls.

iii) This molecular orbital diagram of carbon monoxide is most widely accepted to rationalize its a-donor and rc-acceptor strength. The total number of valence electrons in carbon and oxygen are four and six, respectively; and thus, ten electrons are to be filled in the molecular orbitals of CO molecule. A total of four singly degenerate a- molecular orbitals and two doubly degenerate sets of rc- molecular orbitals are formed. One doubly degenerate set ofrc molecular orbitals will be bonding while the other one will be antibonding in nature. The nature of a molecular orbitals is more complex as three out of four are of bonding character. Initially, the as was thought to be of anti bonding to justify the higher bond order of co+. However, the as is slightly bonding in nature because there is some mixing with the p atomic orbitals of the right symmetry. Out of four a­ molecular orbitals, only a6 possesses the antibonding character, while as goes with expected bonding characteristics. The as is essentially non-bonding and almost centred on the oxygen atom. Moreover, doubly degenerate sets of rc-bonding and rc-antibonding molecular orbitals are also formed due to the sidewise overlap of 2py orbitals and 2p~ orbitals. The rc-bonding molecular orbitals set will be rich in atomic orbitals of oxygen while antibonding molecular orbitals, that are closer to carbon in energy, will be rich in atomic orbitals of carbon atom. However, the problem that why does the bond order increases when an electron is removed from CO still persists. Because we are removing the electron from a bonding molecular orbital, its bond order must be decreased. The possible explanation for the shortening of bond after ionization is that the ionization induces a shift of the electron-polarization in CO ligand. In other words, the ionization occurs as the loss of an electron from a a-HOMO orbital which is mostly carbon-centred; and since the HOMO-a orbital is only slightly bonding in nature, the loss of bonding character is quite small and could easily be compensated by the advantage in covalent character; i.e. the formation of a positive partial charge on the carbon atom increases the strength of the covalence of the bond and thus decreases the bond length. This enhanced covalent character can also be visuali zed in terms of better interaction of two atomic orbitals if their energies are comparable. In carbon monoxide molecule the atomic orbitals of oxygen lie energetically a lot below then the atomic orbitals of carbon; But when the CO is oxidized to co+, the partial positive charge on carbon shifts the atomic orbitals of carbon down in energy, and thereby makes the energies closer to the related atomic orbitals of oxygen, which leads to a stronger interaction when bonds are made.

DALAL D INSTITUTE 438 A Textbook of Inorganic Chemistry - Volume I

, 4 ... ,"' ,' 6cr ',\ ," , , , ,' ,' \ .' , ,' 1, ... . , ,, .. -~ .. LUMO ' ...... ,' 2n ',\·.', ' ' ,.. ,. I tu , _ .. .. t \.. \ -----:':"\\ ' , .. \ ...... , .· \ .. ' ', 2p I 2p I Jp 0 •:,\,, ,' ', •, \ t '\ ' I \ \ \ \ X ~ y ,.- : 1 \\ ', ...... ,' \ ', ', \ \ \. ',r ' ' 11 ' .. " .. ',:, t t t I ', .. \,' ',, " -·.. ,, , ~---. ".. :.. u --.~ -----·, :,~ l 1 J " \ .. ' :· ... ,.--,:: 2p, , 2py ,2p=- HOMO '. II\ ',\ ,' 5cr l \ ' t I \ \ 'I \ '~ ~ ,' It /\ \.'/'.\ t I t I :\;·'' ~,',' ,,'' It/\ ~~,\ 1 \ 1 1 I l ' \ \ I t I ,' \' \. ln: \,,' ',' I / t \ I I ( I \ I\ t i I t t \ ' \ t I I t \ l ,' \ I I ' , ' •' ' ,' ,'' .', \ f t1 ,' ,'\' •',

1, ' ' \ ' 11 1 k'.... ------·\, 4a .. I ---~ ' ' ' I 'I \ \ t I \ \ 2s2 .... \ : .... ' ' ' I ' \ 1 .. I ',, \II • I ' t' \ I ' \I ti ',, " : ·-:~ ...... \ ti ,' ...... >'----. ' "'~~•-~.' · • • · 2s2 3cr

Carbon co Oxygen Pictorial Representation of MOs

Figure 11 . Third molecular orbital diagram of carbonyl ligand.

The MO diagram shown above is ve1y useful in explaining the bonding between metal centre and carbonyl ligand. The carbonyl ligand uses its HOMO for sigma donation while simultaneously accepts electron density from filled metal d-orbital to its n " LUMO.

DALAL INSTITUlfE Main Market, Sector-14, Rohtak, Haryana www.dalalinstitutc.com, +91-9802825820 NET.JRF, Ill-GATE, Ill.JAM & M.Sc Entrance (Chemistry)

Figure 12. The second molecular orbital diagram of carbonyl ligand.

DALAL D INSTITUTE ••••••••••••••••••••••••••••••••••• l~l~fJ1ll~ Ntt'l,I(;J~ •••••••••••••••••••••••••••••••••••••••

This document is an excerpt from the book entitled "A Textbook of Inorganic Chemistry - Volume 1 by Mandeep Dalal", and is the intellectual property of the Author/Publisher. The content of this document is protected by international copyright law and is valid only for the personal preview of the user who has originally downloaded it from the publisher's website (www.dalalinstitute.com). Any act of copying (including plagiarizing its language) or sharing this document will result in severe civil and criminal prosecution to the maximum extent possible under law .

••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••

This is a low resolution version only for preview purpose. Ifyou want to read the full book, please consider buying.

BliiTHISBOOK

DALAL INSTIT1UTE Ma in Market, Sector-14, Rohtak, Haryana W\:VW.dalalinstitute.com, +91-9802825820 NET-JRF, !IT-GATE, !IT.JAM & M.Sc Entrance (Chemistry) International Edition

A TEXTBOOK OF INORGANIC CHEMISTRY Volume I MANDEEP DALAL Table of Contents

CHAPTER 1 ...... I I Stereochemistry and Bonding in Main Group Compounds: ...... 11 •!• VSEPR Theory ...... 11

•!• dn-pn Bonds ...... 23

•!• Bent Rule and Energetic of Hybridization ...... 28

•!• Problems ...... 42

•!• Bibliography ...... 43

CHAPTER 2 ...... 44 Metal-Ligand Equilibria in Solution: ...... 44

•!• Stepwise and Overall Formation Constants and Their Interactions ...... 44

•!• Trends in Stepwise Constants ...... 46

•!• Factors Affecting Stability of Metal Complexes with Reference to the Nature of Metal Ion and Ligand ...... 49

•!• Chelate Effect and Its Thermodynamic Origin ...... 56

•!• Determination of Binary Formation Constants by pH-metry and Spectrophotometry ...... 63

•!• Problems ...... 68

•!• Bibliography ...... 69

CHAPTER 3 ...... 70 Reaction Mechanism of Complexes-I: ...... 70 •!• Inert and Labile Complexes ...... 70

•!• Mechanisms for Ligand Replacement Reactions ...... 77

•!• Formation of Complexes from Aqua ...... 82

•!• Ligand Displacement Reactions in Octahedral Complexes- Hydrolysis, Base Hydrolysis .... 86

•!• Racemization of Tris Chelate Co1nplexes ...... 89

•!• Electrophilic Attack on Ligands ...... 92

•!• Problems ...... 94

•!• Bibliography ...... 95 CHAPTER 4 ...... 96

Reaction Mechanism of Transition Metal Complexes-II: ...... 96

•!• Mechanism of Ligand Displacement Reactions in Square Planar Complexes ...... 96

•!• The Trans Effect ...... 98

•!• Theories of Trans Effect ...... 103

•!• Mechanism of Electron Transfer Reactions - Types; Outer Sphere Electron Transfer Mechanism and Inner Sphere Electron Transfer Mechanism ...... 106

•!• Electron Exchange ...... 1 I7

•!• Problems ...... 121

•!• Bibliography ...... 122

CHAPTER 5 ...... 123 Isopoly and Heteropoly and Salts: ...... 123

•!• Isopoly and Heteropoly Acids and Salts of Mo and W: Structures oflsopoly and Heteropoly Anions ...... 123

•!• Problems ...... 152

•!• Bibliography ...... 153

CHAPTER 6 ...... 154

Crystal Structures: ...... 154 •!• Structures of Some Binary and Ternary Compounds Such as Fluorite, Antifluorite, Rutile, Antirutile, Crystobalite, Layer Lattices - Cdb, Bih; Re0 3, Mn20 3, Corundum, Pervoskite, Ilmenite and Calcite.154

•!• Problems ...... 178

•!• Bibliography ...... 179

CHAPTER 7 ...... 180 Metal-Ligand Bonding: ...... 180

•!• Limitation of ...... 180

•!• Molecular Orbital Theo1y - Octahedral, Tetrahedral or Square Planar Complexes ...... 184

•!• n-Bonding and ...... 198

•!• Problems ...... 212

•!• Bibliography ...... 2 I 3 CHAPTER 8 ...... 214 Electronic Spectra of Transition Metal Complexes: ...... 214

•!• Spectroscopic Ground States ...... 214

•!• Correlation and Spin-Orbit Coupling in Free Ions for 1st Series of Transition Metals ...... 243

1 •!• Orgel and Tanabe-Sugano Diagrams for Transition Metal Complexes (d - cf States) ...... 248

•!• Calculation of Dq, Band~ Parameters ...... 280

•!• Effect of Distortion on the d-Orbital Energy Levels ...... 300

•!• Structural Evidence from Electronic Spectrum ...... 307

•!• Jahn.-Tella.r Effect ...... 312

•!• Spectrochemical and Nephelauxetic Series ...... 324

•!• Charge Transfer Spectra ...... 328

•!• Electronic Spectra of Molecular Addition Compounds ...... 336

•!• Pro.bl ems ...... 340

•!• Bibliography ...... 341

CHAPTER 9 ...... 342 Magnetic Properties of Transition Metal Complexes: ...... 342

•!• Elementary Theory of Magneto-Chemistry ...... 342

•!• Guoy's Method for Determination of Magnetic Susceptibility ...... 35 1

•!• Calculation of Magnetic Moments ...... 354

•!• Magnetic Properties of Free Ions ...... 359

•!• Orbital Contribution: Effect of Ligand-Field ...... 362

•!• Application of Magneto-Chemistry in Structure Determination ...... 370

•!• Magnetic Exchange Coupling and Spin State Cross Over ...... 375

•!• Problems ...... 384

•!• Bibliography ...... 385

CHAPTER 10 ...... 386 Metal Clusters: ...... 386

•!• Structure and Bonding in Higher ...... 386

•!• Wade's Rules ...... 401 •!• Carbo ran es ...... 407

•!• Metal Carbonyl Clusters- Low Nuclearity Carbonyl Clusters ...... 412

•!• Total Electron Count (TEC) ...... 417

•!• Problems ...... 424

•!• Bibliog·raphy ...... 425

CHAPTER 11 ...... 426 Metal-II Complexes: ...... 426 •!• Metal Carbonyls: Structure and Bonding ...... 426

•!• Vibrational Spectra of Metal Carbonyls for Bonding and Structure Elucidation ...... 439

•!• Important Reactions of Metal Carbonyls ...... 446

•!• Preparation, Bonding, Structure and Important Reactions of Transition Metal Nitrosyl, Dinitrogen and Dioxygen Complexes ...... 450

•!• Tertiary as Ligand ...... 463

•!• Problems ...... 469 •!• Bibliography ...... 4 70

INDEX ...... 471 Mandeep Dalal is an Indian research scholar wha is primarily working in the field af Science and Philosophy. He received his Ph.D in Chemistry from Maharshi Dayanand University. Rahtak. in 20!8. He is also the Founder and Director af "Dalal Institute". a nan-profit private educ ational organization in India which is trying ta revolutionize the made af higher educ:atian in Chemistry. He has published mare than 25 research papers in various international Mandeep Dalal scientific journals. inc:ludin g mostly fram Elsevier (M.Sc, Ph.D, CSIR UGC - NET JRF, IIT - GATE) (LISA) and Springer (Europe). Founder & Director, Dalal Institute Contact No: +91-9802825820 Homepage: www.mandeepdalal.com E-Mail: [email protected]

....------·~~ . Rf SUJ·Wl~ S<~Y - YR~1M«IN ... ""'""' .... mr rID'l IS< S<~llY - Y~J.RW ~ ~ S< S

"° en -..:i ==to oo = Z oo --·· ...... --="°-..J \0 iiiiiiiii 00 (.;.)-I ==-- 00...... oo --=•\0 -l--w DALAL N=OO --:i INSTITUTE 0 --N D o~o o ~ b Main Market, Sector-14, Rohtak, Haryana - 124001 I v 0 www.dalalinstitute.com