 Hello everyone, I once again welcome you all to the last lecture of MSP lecture series on Transmittal Chemistry. This lecture I shall consolidate whatever I discussed in last 59 lectures in the form of summary and conclusions. To begin with what I did was I gave a historical background to the periodic table why I gave it is very important to know how many of these people contributed to bring all the known elements in the form of a table to understand their chemistry and also to do comparison and also giving some order as I had mentioned periodic table is nothing but place for every element and every element in its place. So meticulously it was done and it was published by Dmitry Mandeleev in 1869 but however at least 50 years before this concept came into the mind of Dmitry Mandeleev several other all chemists or physicists chemists in general scientists worked very hard to arrange those elements in a organized manner in that context. I call all these people as periodic table scientists you can see here among them who stands taller if you ask me it is Antoni Levasier he changes the perception of understanding of science and chemistry at the time when people were not going in a different direction to propagate the advancement of science at that time he brought the concept of quantitative analysis instead of qualitative analysis and he can be called as father of modern chemistry and of course he named oxygen and hydrogen and also he named several other elements he also discovered silicon and unfortunately at the age of 51 he was guillotined. Next Mandeleev published his periodic table in 1869 but before that triad system came into picture by John Newland and then he also talked about octave and then John Jacob Burgilius named several elements and give symbols for them and when periodic table was published by Dmitry Mandeleev he gave an important statement that physical and chemical properties of elements are periodic functions of their atomic weight but later Henry Mersey through extensive photoelectron spectroscopy he determined atomic number and several properties of elements and eventually he modified the understanding of periodic table giving importance to atomic number and thus it was modified as the periodic functions of atomic number that means physical and chemical properties of elements are periodic functions of their atomic number. Now we know that how valuable the atomic number is that is electronic configuration and number of electrons and once we know the electronic configuration and with basic understanding of periodic trends and periodic properties we should be able to deduce all properties and understanding the reactivity stability etc. And during the same time when Dmitry Mandeleev presented his periodic table Julius Lothar Meyer from Germany was almost ready even one year before but somehow he did not publish it does not mean that he did not contribute his contributions are very significant and due to some reason he did not publish his periodic table that was very similar to what Dmitry Mandeleev presented and however we can see in even in NCRT books Lothar Meyer's plot about trends among transfer elements and of course Glenn Sieberg and Yuri Agenison were given distinction by naming elements with atomic number 207 and 218 after their name and in fact when element with atomic number 207 was named as Sieborgium Glenn T. Sieberg was extremely happy and he said that it is more than this honor of naming element of his name is more than getting a Nobel Prize. In fact these are the only two people whose names were considered for two elements when they were alive and of course one should understand the trends in atomic radii or melting point, boiling point, ionization energy and try to analyze to understand the properties how it varies within the group and also along the period when you start filling from D0 to D10 electronic configuration. For example you can see why Magnus group shows decrease in melting point all these things are clearly spelled out in my lecture please give importance and attention to these things so that you can understand the behavior in a better way. It is very appropriate to remember Alfred Werner for his coordination theory again when he started working on coordination compounds of cobalt octahedral cobalt compounds and square panner complexes of platinum there were no support of any analytical or spectroscopic tools and not only that one even atomic model atomic structure was not known and even electrons were not known in fact he proposed his coordination theory in 1893 but electrons were discovered much later by JJ Thompson in 1896. However he did not leave any stone unturned with his synthetic ability and analytical thinking he could make all possible isomers and also he brought isomeration concept and also he said why coordination number 6 would prefer octahedral geometry when you have coordination number 4 why Saturn molecules prefer square panner geometry why Saturn molecules prefer tetrahedral geometry all those things very nicely he analyzed and he eventually he proposed his coordination theory during his time his contemporary who had more inclination towards organic chemistry Jorgensen was always opposing and ridiculing discoveries of Alfred Werner because he was proposing a theory called chain theory and always telling that no coordination compound can have coordination number more than 3 and also I showed you how the bonding was shown in octahedral compounds of having different number of ammonia and chloride in his chain theory and chain theory was a total flaw but however he was also ridiculing coordination theory proposed by Alfred Werner but in fact it even went to personal abusing level but however he tolerated all those things and he quietly worked hard and eventually he made everything very clear and then eventually he got the Nobel Prize in 1930 and one more thing we should remember is about making an optically active coordination compound having no carbon atoms in fact Jorgensen was again telling one cannot make any optically active compound without having a chiral carbon center so with this what he did was he made this compound you can see there are no carbon atoms only O and N are coordinating he made this chiral compound he isolated both the enantiomers and then for his painstaking work and of recognizing this synthesis he was given Nobel Prize in 1930. So now we know most of the concepts still were using whether it is reaction mechanism or whether it is isomerism or whether it is understanding bonding concepts and of course crystal field theory is a very nice theory to explain bonding among coordination compounds to an extent organometallic compounds but there is also flaw was there and nevertheless it is a fantastic bonding concept and it can explain many things only thing is it does not consider covalency in the bonding metal to ligand bonding. However the best from wellness bond theory that is mixing of orbitals that is hybridization and then crystal field theory about splitting of the orbitals were nicely imbibed into molecular orbital theory to come up with ligand field theory. Now ligand field theory having all these very good ingredients from these bonding concepts can literally explain everything including reactivity stability and all those things. So this is how coordination chemistry progressed from Werner's coordination theory and also in between ISO told you earlier attempts to explain bonding using electro neutrality principle and Keppert's model for using via CPR theory to explain bonding all those things. And of course crystal field theory is very very important in order to understand and to write crystal field splitting diagrams one should remember two things one is relative orientation of the orbitals with respect to Cartesian coordinates and also the direction of approach of ligand towards metal in different geometries. Once we know these things understanding and writing crystal field splitting diagram for any geometry would be rather easy okay. So again to emphasize I am showing you the orientation of orbitals and also the planes we come across x y plane and then x z plane and z y plane. So now if you arrange all the orbitals and if you place ligands coming from different directions to establish a certain geometry we can know now because of this interaction what would happen to the energy and how the degeneracy is destroyed and how they are arranged. Once we know understanding rest of chemistry would be rather easy this is for dx y square and this is for dx y and then this is for dx z and this is for dy z. Once we know these things and also we know the geometry of our ligand field we can write crystal field splitting very easily for any given geometry. So now this is very very important spectrochemical series and spectrochemical series the position of ligands in spectrochemical series can be checked by looking into UV visible spectroscopy of complexes having these ligands. But on the other hand why a given ligand has taken or occupied a position somewhere here or here in the spectrochemical series cannot be explained by CFSC. CFSC can also only tell you where it is positioned but why it is positioned you cannot tell for that one one has to understand the nature of the ligands and what kind of electrons they have and where in the donor orbits are located or whether it has donor and acceptor properties or it has only donor property or it has both donor and acceptor properties. So in that context these pictures are very very significant. So here you can see I have written three diagrams again I am emphasizing we talk about pure sigma donor ligands in that case CFSC would remain like this and when we consider a sigma donor and pi donor ligands for example low laying filled sigma donor and low laying filled pi donor orbits are there in that case what would happen because of overlapping and generation of molecular orbitals the CFSC drops significantly that is the reason these ligands are called as weak field ligands. So the CFSC does not tell why they are weak field ligands because of the these two here low laying sigma filled sigma orbits and filled pi orbits having low energy compared to metal T2g would signify why they are weaker ligands. And similarly if we look into sigma donor and pi acceptor low energy filled sigma orbits are there high energy empty pi orbits are there in this case what happens because of their overlapping the CFSC in this fashion CFSC increases. So that means we should remember this one the classification of ligands should be based on these three that is two sigma donors and sigma donors and pi donors and sigma donors and pi acceptors. Once we know those things understanding chemistry and utilizing them in some application would be very easy. Now let us look into M O diagram for square panner complex if we just look into CFSC crystal field splitting here this is the gap that determines CFSC among square panner complex and again here if you just look into it this is the gap that we call it as frontier orbits I would say and this is HOMO and LUMO gap here and if you consider here 8 electrons 8 electrons are filled here so up to here 8 electrons are filled and then this will be HOMO and this will become LUMO. So that means by extending this one considering this crystal field splitting diagram and then considering the what kind of hybridization one can anticipate for square panner complexes getting information from VBT and then we consider these two and put into molecular orbit theory this ligand field theory comes and it can explain very nicely all those things and also I have given Mullikan symbols for various d orbitals just go through it and just look into it and try to understand. So now one more M O diagram I have given here for nickel tetracharbonyl you can see here nickel tetracharbonyl this lone pairs are placed here higher in energy among all and this one essentially should go to the metal sp3 orbitals to establish metal to ligand bond metal to nickel to carbonyl bond but however if you just look into this diagram they are not participating there is no overlapping of this one with S and P because they are too high in energy so that means you should know the fact that NiCO4 does not have sigma or bonding at all that means how this molecule is formed it is because of back bonding only you can see here so these T2G electrons are getting placed in the molecular or generated by pi star and T2G of metal so that means only the back bonding from nickel to carbonyl oxide anti bonding orbital is responsible for the existence of NiCO4 so that is the reason they are very unstable and also they are volatile whereas in case of metal carbonyl such as chromium hexacarbonyl tungsten or iron pentacarbonyl we have seen the participation of both sigma as well as pi orbitals in fact all metal hexacarbonyls are stable and solids with having moderate stability so now these four diagrams will tell you non classical ligands having sigma under and pi acceptor capabilities carbon monoxide and phosphines and also fissure carbene and n heterocyclic carbene all of them are non classical ligands having sigma donor and pi acceptor capabilities and of course there is relative difference in their donor and acceptor properties carbon monoxide may be very good sigma donor and also good pi acceptor no doubt but phosphines can also compete well with carbon monoxide in terms of their sigma donor ability and pi acceptor ability but in contrast to carbon monoxide we can vary these things we can vary these properties to an extent that it can even perform as a better pi acceptor compared to carbon monoxide when we have electron with drying groups or electro negative substituents on phosphorus that means we should know that electronically we can tune the phosphines to make them better than carbon monoxide for example if you put more electrons releasing groups on phosphorus it can be a good sigma donor and a poor pi acceptor on the other hand if you put electron with drying groups on phosphorus it can become poor sigma donor but very good pi acceptor so this kind of flexibility in its synthesis you cannot come across in carbon monoxide that is the reason the tuning is very easy and hence phosphines are very popular when we use metal complexes containing phosphines as catalysts in homogeneous catalysis for several organic transformations and similarly fissure carbines also there here also back bonding is there back bonding one can anticipate in the same way as carbon monoxide but here already we have lone pairs within the ligand as a result what happens this intra back bonding is more facile compared to inter back bonding that is from metal to ligand as a result what happens they become poor pi acceptors so this also you can call this as intra back bonding also you can call it as negative hyper conjugation same thing is to in case of n heterocyclic carbines also you should remember n also has a lone pair this lone pair can also go to the pi star of carbine as a result what happens they are also poor pi acceptors but they are good sigma donors so this is how you can compare these non classical ligands in terms of their donor and acceptor properties and then 18 electron rule is very important it is not a must to have a stable complex because many square pen are complexes with 16 electron are stable for example rhodium 1 iridium 1 and also all d8 system nickel 2 palladium 2 platinum 2 gold 1 all those things but here 8 electron counting 8 electron give some idea about their possible utility in some reactions and other things for example if they are 18 electron complexes you cannot use them for oxidative addition reaction or catalysts prior to that one what happens you have to get it off a couple of ligands or you have to remove some electrons so that it is ready for oxidative addition reactions and also it is very interesting to count electrons so for the reason I have taken this interesting molecule again we have here rhodium and iron and we have 5 carbonyl groups are there and 1 C7 H8 is there cyclohexate triene is there and that I have shown here so now let us see how it satisfies 18 electron rule first you should think of a formal rhodium to iron bond and also why I have put more carbon monoxide ligands on iron is because it has less electrons compared to rhodium it is a d7 S2 system whereas d6 S2 system so now 2 are there and one rhodium rhodium rhodium iron bond is there and now you should place in such a way that both of them would be having 18 electrons it is 17 electron so that this comes through one comes through rhodium iron metal metal bonding so this is how you can show eta 4 and eta 3 so this is again very interesting so like that many examples I have discussed go through it and also you can find lot of examples in textbooks try to solve them or best thing is every time you come across a matter complex try to count electrons to see whether it satisfies 18 electron rule or not so now it is about metal to metal multiple bonding this is very important with square panor complexes and having eclipsed geometry of course I have discussed it in length how they identified first in the rhenium complexes in the group of FA cotton when he was in MIT and now we know that how to explain the bonding up to 5 bonds not 4 bonds like quadruple bond up to 5 bonds are possible between 2 metal centers and then how you know the bond formation takes place can be readily explained using even molecular picture like this and here you should remember the fact that dz square and for this one what happens to metal complexes having square panor geometry should be eclipsed to each other and in this case if you just ask me yx dx square y square is not used because that is already used for the formation of metal to ligand bond if you recall dsp 2 hybridization from wellness bond theory so that means 4 orbitals are left here dz square dyz dxz and dxy now one can comfortably use from 2 metals to establish metal metal bond like this so this one is a sigma bond head on collision dz square dz square and dxz is like something like this and then dyz is something like this they are degenerate they can accommodate 2 electrons each and then we have dx y is there so this is a weak interaction something like this so one is this dz square one is dxz another dyz and then this is dxy dxy will be like this so now that is called delta bonding between them weakest two overlapping among orbitals what would happen to the number of electrons one have d1 one electron is there so then you can have one electron from each results in sigma 2 double bond 3 triple bond and 4 quadruple bond if you have 5 again we start filling anti-bonding orbitals so triple bond d6 double bond d7 single bond and d8 everything is filled so bond already 0 you cannot see no formal metal metal bond can be seen in d8 system you can see that one again I am showing you here d4 system how electron filling takes place in this order to see quadruple bonding so all d4 system is square panel geometry have possibility of showing quadruple bonding okay so now it is even possible to have 5 bonds that is quintuple bonding for that one what happens you need one more orbital other orbital possible orbit is dx minus y square for that one you should ensure that metal has not utilized this dx square y square for establishment of metal to ligand bonding in that case we have to go for further lower coordination number for example if you take here in this case it has not used any of the d orbits for making metal-metal bonding let us assume it has SP orbits are there these 2 SP orbits have used this one here and this one so now all the 5 orbits are left and it also has 5 electrons in d orbitals now dx y and dx y square at an angle of 45 degree are degenerate similar to dx z and dy z so you can have here 10 electrons so bond order is 5 so this is how you can explain very nicely using m o diagram quintuple bonding as well I have given quite a few examples again go through it and in case if there is a problem always you can write to me and this is important about hydrogen bonding to metal in fact it is very significant h to h h bond is quite strong and it is endothermic it is not easy to break as I mentioned if you take any unsaturated hydrocarbon and put high pressure hydrogen into it and in a closed vessel and if you try to heat it for several hours even hydrogenation happens with very very low conversion about 5 percent or 6 percent but on the other hand you add a metal complex so that can happen even at room temperatures why that happens because how very nicely it drift the electrons present between hatch through sigma bonding and also it pushes its own electrons through back bonding to sigma star so that means you are taking away bonded electrons and you are pushing electrons to the anti-bonding as a result what happens h h bond becomes weaker and then earlier it is a eta one bonding it becomes what happens very nicely it adds oxidatively to form 2 m h bonds so this this is very very significant because of this property metal complexes have been extensively used in organic transformation in homogeneous catalysis so whether it is a h h bond whether it is ch bond whether a cc bond or any other hetero atom to hydrogen bond they can do very conveniently as a result we come across the application of these complexes in many organic transformations of course still we have not succeeded or achieved to use in industrial scale the cc bond breaking for that one one has to make very very ideal compound where it is highly electron deficient and the ligands are of poor sigma donor and coordination low coordination is there in that case what happens it should be ready to grab literally anything that comes on its way to expand its coordination number in this case probably let us say if you put octane it can go very nicely and it can break into 2 butyl groups if that happens with base metals such as iron cobalt nickel or something one can make fortune out of it so there is enormous enormous scope to activate cc bond using metal complexes but with cloverly designed ligands and of course here I showed why NO plus is stable because if you once get rid of this one electron from pi star it will be having bond order of 3 that is the reason it would be more stable and also here I am showing you now once this electron is gone and now NO plus is there this can also behave very similar to other non classical ligands and act as pi acceptor ligand you can see here I have shown sigma donation as well as pi acceptor so NO can also be used as a pi acceptor ligand and some metal complexes we can see these things. And when we talk about phosphines I mentioned about electronic properties and steric properties are very important the steric influence the magnitude of steric influence can be measured using Torlman's cone angle what happens here you take the ligand make a bond to the metal with a distance of average distance of 2.28 and strong units of 228 picometer now imagine a conical surface at the metal that encloses the van der Waals surfaces of ligand substituents over all possible rotational orientations how this controls the steric attributes you can see by looking into the cone angles shown by different ligands having different substituents as bulkiness of the phosphorous substituents increases cone angle increases in that case what happens you can have because of steric congestion you can stabilize metal with the fewer ligands in that case what happens we are automatically we are generating a low coordinated system having less electrons in that case what happens these compounds are electron deficient and also co-ordinatively unsaturated as a result they can readily undergo oxidative addition for example if you take compound here phosphines four phosphines are there in tetrahedral 18 electron system is there the moment you put into solution because of steric congestion two ligands go out dissociation would be very easy and now let us look into the metal to halide bonds in metal to halide bonds also I discussed it in length about how certain ligands certain metal complexes have tetrameric structure and some of them have dimeric structure take even aluminum itself aluminum fluoride if you look into it it has a tetrameric structure like this whereas aluminum chloride has a dimeric structure like that AlCl3 become Al2Cl6 Al2Cl6 it is not aluminum actually it is a metal complex here it is a transfer metal complex but nevertheless the reason is the smaller size when the smaller size is there because of more electrons are there if assumes a fluoride assumes a bent structure when it is bridging to two metal centers in the bent structure what happens two cations come very close to it they repel as a result what happens they would try to have a linear geometry in that case if you want to see association that has to be minimum of tetrameric or in some cases trimeric also we come across the preferred one is tetrameric hence if you look into CuF22 plus or CrF22 plus although it looks like they have linear geometry it is not linear geometry the composition of copper to fluorine is 1 is to 2 and but they have octahedral geometry something like this and then oxide tradition is very important and I also discussed in length about different possible mechanisms we have 3 bond concentrated addition is there and nucleophilic substitution reactions are there and also radical mechanism also there and also I discussed all those things and you can see polar solvents are going to the transpositions whereas nonpolar bonds are going to the cis positions so we can see clearly distinguish between concentrated addition and also nucleophilic oxidative addition and also I discussed it about a stereochemical consequences also and then trans effect is very important when it comes to substitution reactions in square panner complexes what one should remember is in a given complex electron attracting ligands are epical and electron repelling groups are trigonal planar so when the incoming ligand is there a pair having trans influencing group and a group trans to it and the incoming plane will be trigonal planar and other two will be axial and in this case you have to identify which is electron attracting group and which is repelling group and accordingly if you generate the intermediate the moment you generate intermediate you will come to know the conformation what kind of conformation we are going to get at the end of substitution is completed and of course in case of octahedral complexes I did mention about substitution how it happens incoming ligands can come to come on the same side of the group or they can come on the opposite side and accordingly what happens you can see how that influences the formation of cis isomer or trans isomer and also I also discussed about stereochemical changes the stereochemical consequences in a substitution reaction on octahedral complexes and when it comes to redox reactions we have two type of inner sphere coordination and outer sphere coordination and in case of inner sphere coordination theory we need a bridging ligand and this is how the intermediate would be there and you can see here once electron transfer is over this also moves towards the other one that that is getting oxidized and then of course in outer sphere mechanism we have to keep frankendon principle in mind and now we can see here t2g eg he is there in this one is a high spin complex where it is a low spin complex before electron is transferred both of them should have a optimum bond length and bond angle and now you can call it as intermediate stage where electrons can run smoothly so that this also does not disobey frankendon principle once the electron transfer takes place they will revert back to different one so this becomes high spin and this becomes low spin and then spectral interpretation I made an effort to make you familiar with you know UV visible spectroscopy and also NMR spectroscopy to an extent IS spectroscopy so that you can characterize those compounds are if you come across some spectra you should be able to interpret and various methods and how we can arrive at the structure all those things I have shown in this chart and of course angular meant quantum number and spin angular momentum how they interact I have shown here very nicely LS coupling and LS coupling is also very important when we talk about UV visible spectroscopy and also in when we look into magnetic properties and then of course I classified all de-electronic configuration to four groups here there is a significance why we have why I have done like this here you can see one the charge transfer transitions if the compounds are color it is because of charge transfer in this one ligand to metal in this one metal to ligand and in these cases we have one electron one less than half field one more than half field and one less than completely filled here in the same way we have two electrons and two less than half field two more than half field and two less than completely filled so these complexes show invariably one dd transition here they show invariably three dd transition of course d5 is spin fermentant and leopard fermentant and compounds are weakly colored or pale colored compounds and of course all those things I discussed in depth and this equation is very important when when we talk about NMR and using this equation we can literally explain anything about NMR transition and other things and what one should remember is if you look into spin selection rule delta s equals 0 so that means basically a electron with upward spin should go like upward spin only whereas in case of NMR its plus or minus 1 the flipping of nuclear spin I mentioned so electron with upward spin should go to exact state to be having a lower spin alpha becomes beta or something like that so this is very important and you can see here in this diagram precision results in the flipping this is through radio frequency applied in a direction perpendicular to the magnetic field you can see clearly here so you should remember these things and then magnetism I did not have time to discuss about magnetism of course you can find these things in standard books pretty easy and we use two equations and of course here we are using s is the summation of number of unpaid electrons here for example s if one electron is there s equals half two electrons are there one and then three electrons 3 by 2 it goes like that here n is number of unpaid electrons both are essentially same and if we can also use this one where of course you know already how to find out L as well as s you can find out mu from this equation as well or in case of lanthanide and actinides we have to find out G G is 2.0023 and if in some cases only whenever we come across spin only treatment we can always consider G as 2 the splitting of orbit levels is larger relative to KT that is Boltzmann constant then one can use this equation here G into square root of J into J plus 1 G can be calculated provided we find out from electronic configuration what is s and what is L and of course J one can also use value L plus or minus s depending upon whether the orbital is completely less than half field or more than half field if it is more than half half field we use L plus s if it is less than half field we use L minus s where we should consider you know orbital contribution we have to see they should be differentially especially T 2 G orbits in case of octahedral complexes and T 2 orbits in case of tetrahedral complexes should be differentially occupied in that case what happens you can see spin orbital contribution the moment you look into the electronic configuration you should be able to make out whether spin orbital contribution is coming or not for example in case of octahedral T 2 G 1, T 2 G 2, T 2 G 4 and T 2 G 5 have unsymmetrical filling in that case you come across orbital contribution and same thing is to in case of tetrahedral X Z of course here G should be removed because it does not have centrosymmetry it should be T 2 1, T 2 2, T 2 4 and T 2 5 for tetrahedral complexes and you can see here with 45 degree rotation DX Y can become DX minus Y square and similarly with 90 degree rotation DYZ can become DX Z. So, at last I dedicate this lecture series to my beloved parents my father and my mother one year before I submitted my thesis my father passed away and two years back my mother passed away and these people taught me high ethics in me and because of them what I am today. So, I dedicate this lecture series to my parents and also you should remember parents always work hard to make you better citizen and educated and they sacrifice everything. So, in that context always try to remember parents and of course in some cases what happens I have seen students parents force their children to opt for a particular topic in which the student a son or daughter is not interested in that case what happens you should try to convince them why you are interested in this one and why you are not interested in what they are imposing certainly you can convince them and you can take a right path and achieve greater success and I am sure I had conveyed some chemistry through these 60 lectures and I have put lot of effort you should remember lot of effort I have put in generating some of the slides to convincingly teach some chemistry and when you understand the chemistry behind these 60 lectures and you know pass exams with good grades and if you are at the end if you think that yes I got something out of this course I will be very happy and in case if you have any problem you can always write to me and later when you achieve higher success and in case if you think that this course has contributed to your improvement your knowledge and when you achieve greater success and achieve something and make a mark and if you just send me a mail I will be the happiest person and that brings millions worth happiness to me. So, with this I will show all very very best and God bless you all enjoy chemistry thank you so much learning never stops even now I am learning I can say without any hesitation I am a good student of learning underlying good student of learning because I do not claim anytime that I am a teacher because I have to learn a lot even now and that means no matter what you do learning should never stop. So, learning should continue so that we can have more and more knowledge and when we have enough knowledge it is our sincere duty to dissipate it to others thank you once again.