 I will start on magnetism, before going to magnetism I think one or two application what we were discussing for you know coordination chemistry I will show in here. Sometime we do not realize that the simple high spin, low spin configuration can give you something very very important. For example, let us say you have a complex which is low spin it has one color, low spin you know what sort of transition you do expect, it can vary depending on the compound. Let us say you have a given compound the compound is low spin. If you give the temperature, if you heat the complex what you can have is you can convert the low spin compound into high spin, because low spin means what those spin cannot go in the easy orbital let us say t 2 g to easy orbital. Now as soon as you put heat or let us say laser light some of the spin some of those electron will be now traveling to the easy orbital t 2 g to easy. Now the color of that compound will be different, it could be white to red red to white or whatever it is right. So, by changing these something like display you see lot of these color display you know in big audience or big auditorium or even display in the on road side somewhere else. So, basically let us say it is one color the moment laser light is you know signing on this display what happens it may be it may be something showing a particular thing particular let us say name written whatever you want to happy but they wish that something you have wished me that can be written over here on the board just by signing those laser lights that is nothing, but changing high spin to low spin configuration. Lot of things can be done and it has been done without realizing we are seeing those. Other form of these sort of high spin low spin configuration can be used in your money card or ATM. Let us say you have a debit card you have 10,000 rupees every time you pick up money let us say first time you pick up 2000 rupees from ATM machine right. Now so, what can happen is a selected amount of laser light can be irradiated on your card because 2000 rupees will let us say be selecting by default how much laser light to sign. There by some of the complex will go from high spin to low spin or low spin to high spin let us say low spin to high spin specifically you are putting light. So, low spin to high spin will be going next time when you are punching the card again the machine can read how much money you have left let us say after 10,000 minus 2000 8,000. This way let us say at the end you have 1000 rupees you want to draw 5000 rupees from that instrument will not allow. So, these are also technique these are different ways to take advantage of this complex this is something one paper has already come and only problem is so far this technique is little bit expensive that is why we do not see it in the market right now, but soon enough it will be make hopefully made cheaper then you can you know the technology itself is coming expensive that is why it is not in the market, but in principle it can be done. So, lot of the practical application just by signing light since just by signing light you can change the electronic configuration of a compound of course, you have to choose the right compound right wavelength right everything let us say, but once you have that right combination you can do one that something like this right also other thing of course, you know that you have a color less compound you add something high spin to let us say low spin complex form or low spin to high spin complex form something like you cannot read here this is a iron aqua complex which is color less you the moment you add phenanthroly into it high spin complex becomes low spin complex color changes another. So, this is of course, sometime you can use it for magic lot of other application you can have simple color change other things for example, if you have let us say this red complex red complex is due to the low spin complex red complex is due to the low spin complex for example, you are starting with that the you are heating it. So, this is the temperature initially it was 250 Kelvin that is almost like room temperature let us say you start from there you keep on heating nothing happening nothing happening select at a selected temperature now this low spin to high spin transition is going on then what you will see all of a sudden at a particular temperature this red compound is becoming white ok. So, at that let us say this is 325 this is becoming white now that white compound you can try to pull down it will not follow exactly same pathway because the relaxation of the spin like spin was up spin has to go down that relaxation need not be necessarily following the same path you have excited something the relaxation means coming back from the you know the easy level to T 2 G level need not follow the same temperature profile what it can happen is at after reaching this white color it will take quite sometime to come back to the red color. So, that even if you are decreasing the temperature still it stays white and at a particular temperature cooling down at a particular temperature can bring you red. So, these are nothing this is like a very good I mean you know some these sort of you know behavior you can apply to something which may be let us say I mean it could be let us say what I said for money card your ATM card it could be for other display device lot of other things you can you can do. So, display device for example, it is here you just sign the light. So, it is getting heated thereby. So, red color or let us say purple color it is coming white color even if you cool down significantly these white color may not go back to red very quickly, but then again there are different material which can relax faster that means high spin to low spin it can come down faster. So, you sign the light the whatever we says whatever writing is there you see it you take off the light it goes back to the white or red or blue or sorry this is purple again. So, you can basically dictate the term you can tell what you want thereby which complex to pick you want to sign the light from let us say violet color or red color you want to go to white color and you want to stay in white that is one of the mode or if you want to go back right after switching of the laser that can be also possible. So, these are nothing, but application in different display which you can have based on the synthetic chemistry knowledge of course, lot of start up companies and lot of other related application in material science has already come up these are something of course, you can in future if you are looking for a start up company something that this knowledge it necessary it not necessarily this knowledge it is some other knowledge you read in let us say in fourth year fifth year or sorry fourth year. So, you can you can take it off and try to set up a company from these simple ideas if there is none existing. So, that is I guess that is that knowledge sharing and today we will discuss mainly magnets ok. We were discussing magnets in the last class simply magnets are nothing, but having or magnetic compounds are nothing, but having unpaired electron that is what we were discussing. More than unpaired electron better the magnetic moment or higher the magnetic moment magnetic values will be high ok. If you have paired up all the spin paired up if you have unpaired electron, but those unpaired electron are not unpaired they are pairing it up then you are losing the magnetic value right magnetic moment value. So, all the complexes can potentially therefore, give you magnetic moment because all of them are having electrons. Now, the electron as we were say saying electrons are rotating around its own axis that is the spin value it is spinning that is why it can give you one type of momentum ok or spin or spin angular momentum or sorry it is called spin only values for magnetic moment or it can rotate around the orbital ok. There is a nucleus surrounding it the electrons are rotating. So, these are the two types of motion that can give you magnetic moment, but what we are saying usually you do not have to worry about the orbital component only the spin only value good enough because ligands are restricting the electrons because they are overlapping effectively restricting the electrons to rotate around the orbital. So, therefore, since the electrons cannot really balance electron mind you not the inner electron balance electron not effectively able to rotate around its own orbit or rotate along its orbit you end up getting only spin component only spin magnetic moment value you get ok. Now, also we were trying to tell you that some cases you have to have spin value plus some orbital contribution why is that that simply because those whenever one orbital to another orbital transition is possible I guess last class we were trying to discuss. So, let us say d x y to d y z to d x z these transitions are allowed transition because by rotating just 90 degree you can interconvert these orbital. Therefore, you can see there is a magnetic component let us say from x y direction to a x z direction. So, thereby there is a some some sort of magnetic contribution on those z direction it is not necessarily ligand is holding the electron completely it is retarding it it is preventing it, but not 100 percent. The moment electron can transfer from one orbital to another orbital that means, the direction changes x y direction to x z direction some component will be arising that is the one going to give you the orbital contribution ok I will come back to that again ok. Let me tell you again simply electron can spin therefore, magnetic moment values can come out of it, but opposite spin can cancel each other as we were trying to say ok. Overall I guess overall we in terms of mathematical calculation we can have this equation where essentially you are keeping your molecules in a magnetic field and that magnetic field is going to be your H. So, in let us say this is the magnetic field of H here you are keeping the compound right. So, how much magnetization or how much effect this molecule is going to feel that is dependent on the magnetic field that H plus its characteristics its nature what can it be magnetized pretty easily that is the term called I ok. So, any species kept in a magnetic field is going to feel the field itself plus its inherent behavior that will try to make it magnetized. So, that is the I component. Now so, intensity of magnetization how quickly it can or how greatly it can orient with respect to that magnetic field ok. Now, if you do the math so, B by H if you divided by H, B by H will be 4 phi I by I by H right. This term is called this kappa or the magnetic susceptibility ok. So, this is the term kappa is the magnetic susceptibility. Now, from there you can do the following math simply there is kappa by rho which is the density of the species density of the molecule that will be the gram molar gram magnetic susceptibility multiply that with molecular weight that will be molar susceptibility. So, this I by H term you divided by rho simple its density of the molecule you get chi g or x this magnetic susceptibility gram magnetic susceptibility. This term you multiply by molecular weight you get molecular or sorry this molar susceptibility ok. This is just simple math you have this equation divide by H you get I by H which is kappa divide kappa by rho that is going to be your gram susceptibility or mass susceptibility. Mass susceptibility multiply by molecular weight you are going to get this molar susceptibility it is something I think you have studied before. Now, once you have that molar susceptibility that is corresponded with the magnetic moment value this is the simple equation. Now, from there you can get the magnetic moment value of a compound right. Of course, mu you can calculate what it is coming it has a temperature component. So, what it tells you is the temperature is going to affect your magnetic moment value. We are going to see how it is affecting. The magnetic moment value is the one we were talking it has two component that is spin component and the orbital component ok. Now, this magnetic moment value can give you the idea about the complex itself what it is made of how many unpaired electron it has. This is a experimentally measurable quantity you can measure the magnetic moment value and thereby you can get crucial information about your let us say unknown compound ok. It can give you number of unpaired electrons present high spin low spin it can give you the spectral behavior you can it can also tell you something about the structure of the complex. So, what all we are saying is if you have an unknown complex you can measure the magnetic moment value of it and thereby you can try to tell what that compound is made of right. How the equation is equations are we have seen in here these are two different equation one is this one another is this one as long as you know the relationship between these two equation you are good to go. This is simple connection between them you just figure it out between these two equation this equation and that equation ok. They are connected by this kappa i by h and then kappa divided by your density will give you molar susceptibility and then multiplied by molecular weight you just look two minutes it should be clear right. So, based on these equation it is expected usually one of the map is given usually we get one question at least based on these two equation they are interrelation some value will be given and thereby you have to calculate the magnetic moment let us say ok. Usually also in I think maybe it is in the tutorial question as well I forgot ok fine. Now we were talking in the last class as well and today itself also we have two component orbital component and spin component the resultant one is going to be the mu total right, but this orbital component is going to be nullified or it will be diminished decreased not necessarily you can prevent it 100 percent ok. That is the orbital contribution usually we do not have to worry about orbital contribution you can calculate just mu spin only. The equation for calculating this mu total by taking this orbital and spin contribution is this one ok alright. Now what happens? So, the capital S this S is number of unpaired electron their spin if it is 3 unpaired electron half plus half plus half 3 by 2 L L will that will come will come for the lanthanide section it is the summation of usually M L right. So, for d orbital it is let us say plus 2 plus 1 0 minus 1 minus 2 will come for the lanthanide from there we will discuss. Anyway you do not have to calculate for d block element you usually do not have to calculate the L value you can only plug this equation for the S value ok alright. So, we have two component once again only spin value is good enough what you nail it down further is root of N multiplied by N plus 2 N N times N plus 2 root of that that gives you for 1 unpaired electron 2 unpaired electrons 3 unpaired electrons 4 and 5 and so on what would be the magnetic moment value. So, by knowing how many unpaired electron is there pretty much you can be confident what will be the experimental or experimentally observed magnetic moment for pretty much a lot of cases. Now so, that is the magnetic moment value, but often what you see is at the end of it the experimentally observed magnetic moment value is slightly higher sometime lot higher how those are coming from or where they are coming from that is due to the assumption that this component does not exist ok. We bring them back to explain it ok. So, when you need to when the orbital angular momentum that nu L part comes in ok. It comes in when you have degenerate orbital we have degenerate orbital if the orbital was not splitted then this component would have been high if 5 d orbitals were degenerate then interconversion would have been possible much easier or 5 of the or 5 of the orbital it can interconvert. So, electron can interconvert between 1 2 3 4 5. So, therefore, the orbital sorry orbital angular momentum value would have been higher since in octahedral field for example, or tetrahedral field it is splitted into t 2 g e g or e t 2 we are going to get little less orbital angular momentum value ok compared to unsplitted d orbital right. Now, of course, interconversion leads to some sort of nu directionality x y to x z z is nu x z to y z y is nu right. So, that is the one contributing for your little bit more momentum right. Now, just degeneracy is not good enough why because you should be able to interconvert also for example, d x 2 y 2 ok this is the last warning ok. It is a big class it is if it was a small class I would not have mind too much because I know what exactly goes on ok please have some respect ok. So, what we are trying to have is t 2 g e g e g d x 2 y 2 and d z 2 by no way you can interconvert. Therefore, in e g you from e g you cannot get any orbital angular momentum value only possibility is t 2 g because the d x y d y z d x z are interconvertible ok. Of course, if they are having same spin you cannot interconvert right. So, let us say t 2 g 3 1 1 1 all 3 of them are having same spin you cannot interconvert fair enough. So, inter there they should be similar shape in size d x y d y z d x z are the same shape in size there should they should be interconvertible and the orbital must not contain electrons of identical spin that is the criteria for getting some orbital angular momentum is it clear? So, t 2 g 1 you can get orbital angular momentum because t 2 g 1 that 1 unpaired electron can be either in d x y d y z or d x z 3 different orientations are possible. t 2 g 2 is possible t 2 g 3 is not possible t 2 g 4 once again is possible t 2 g 5 is possible t 2 g 6 is not possible ok in t 2 g 3 all 3 are having same spin from where to where you will interconvert. See t 2 g 1 means d x y 2 d y z you can go interconvert means 1 means they have to exchange if there is no scope for exchanging for how will you exchange ok same spin t 2 g 3 means 3 unpaired spin in the same direction spin multiplicity same direction they will be having you. So, only so far as we see only t 2 g 3 will not be able to give you yeah ok yeah that I am coming yeah next slide. So, that interconversion will be having some contribution not as great as let us say t 2 g to t 2 g configuration. So, t 2 g to t 2 g I mean interchange will give you little bit more orbital angular momentum value compared to e g to t 2 g conversion that is that is what the next slide is all about. So, d y z d x y and d x z these 3 orbitals are interconvertible no problem ok over here that is the interconversion is shown. So, you just so you just rotate by 90 degree you will be able to rotate d x y. So, this plane to that plane to that or whatever these 3 different plane you can see. Now, as you see d z 2 and d x 2 y 2 are not interconvertible. So, from purely from easy orbital just easy orbital itself cannot give you any orbital angular momentum value. So, that you know the spin only value is only considered ok. Now, of course, what your friend trying to say is d x y is convert can be converted to d x 2 y 2 yes and thereby once you can convert d x 2 y 2 into d x y then you can interconvert d x y to d x z d y z and so on. So, t 2 g easy mixing if you can have then you will be able to get better orbital angular momentum value, but usually for mixing those energy has to be close enough if the gap is very high that mixing is not going to be possible right ok. So, we all hopefully by now understand that it is angular momentum or this orbital angular momentum and spin momentum value are important usually spin only value is good enough, but in some cases you have to talk about orbital angular momentum. Actually that is makes it you know little bit important or interesting otherwise whatever unpaired electron is there you will just end up calculating based on your calculator right. That is not fun of course, the exam questions are asked at least one two or so on orbital angular momentum ok when orbital angular momentum is there ok. Now so, this is the same thing what I was trying to say d 1 can have these three different contribution for example, titanium 3 plus is having d 1 electronic configuration and therefore, orbital contribution will be there for example, d 2 vanadium 7 plus. So, how the question would be let us say a complex is given where vanadium is sorry vanadium 3 plus vanadium 3 plus and you are asked whether it will have any orbital angular momentum or not or in some other form it will be asked indirectly, but mostly definitely I can assure you at least one question will be there on orbital angular momentum at least if not two ok. So, there you can have two different or three different configuration orbital contribution possible yes ok. Now this is something you do not have to remember, but you can justify. You can go through each of those one by one. So, d 1 orbital angular momentum possible yes you can perhaps not read from here that is ok. So, what we have tried to do here is given you the complex different complex and their electronic configuration d 1, d 2, d 3, d 4 up to d 10 and then you have to write down t 2 g easy electronic configuration.