 Hello and welcome to this next segment of CD and MOSBA spectroscopy for chemist. My name is Arunam Dutta and today we are going to discuss about some applications on MOSBA spectroscopy for understanding ferrocene, ferrocinium kind of system. So, in the previous segment we are talking about how we can use MOSBA spectroscopy and try to differentiate between ferrocene versus ferrocinium system and what we have found over there that ferrocene which is having iron in plus 2 state give us a very nice separated doublet signal in MOSBA spectroscopy. So anytime you are drawing it we should draw it such that we are actually defining the axis one is the transmittance and one is the velocity. So over here they are very well separated the delta eq value is close to 2.39 millimeter per second and if we take these two values and take an average of that which will be the delta value which is coming around 0.53 millimeter per second. Now when we actually oxidize the system so when you go to iron 3 plus over here how does it look like? Very interestingly found that this almost become a singlet where there is a negligible delta eq value close to 0.1 millimeter per second in this particular scale we are showing at 2.4 it is almost negligible. But interestingly the delta value remains almost same and we have discussed why we are seeing this that is because over here when you go to ferrocinium the iron plus 2 becomes iron plus 3 but to stabilize it more electron density is actually coming from this cyclopentadienyl ring to the iron center. So at the end the actual electron density present on the iron remains same whether it is ferrocin or ferrocinium iron and that is reflected with this isomer shift values that it remains almost same whether it is ferrocin or ferrocinium. So this is the ferrocinium and this is the ferrocin and now the only telltale difference between ferrocin and ferrocinium is the isomer shift value and isomer shift value shrink down in ferrocinium that is because when it is becomes iron plus 3 it is actually a EPR active system or parametric system which has a spin of half and due to this strong interaction between Cp rings and iron plus 3 it is also generating a lot of orbital moment electrons are moving around it and this orbital moment and this spin moment actually present next to each other. So we create a good amount of spin orbit coupling and this spin orbit coupling what is it does it creates very closely lying states which are known as Kramer doublets and this Kramer doublets ensure that you have two closely lying system and this particular iron plus 3 system populates in both of them and very interestingly either of these doublets is having an electric field gradient but they are opposing in nature. So that is why the actual EFG that I am going to see on an average it is going to be close to 0 and which is reflected almost negligible quadruple gradient over here. So quadruple splitting is almost 0 over here so that is what we are seeing. Now next goal is that can we use this information to understand further electronic distribution in different ferrocin derivative. So let us take one example of such kind. So this is the number 8 example we are taking which we say about mixed valence bipherosins. So what is mixed valence bipherosins we would go there what is a mixed valence compound. So mixed valence compound means that you have at least two metal centers present one say Mn plus and other say Mx plus and these two molecules are present over here in different oxidation state. Now there are three possibilities how they are going to interact one possibility is that they actually present with their localized charge that means this N plus remain N plus X plus remain X plus they are not changing their charge at all. So they are fully localized and that is known as the class 1 mixed valence complexes when they are 100 percent localized. Then there is a system possible and let us take me some examples so that we can understand it better say one is iron plus 2 and the other one is iron plus 3. So in this localized system it remain in iron plus 3 it remain in iron plus 2. Now say another system I have iron plus 3 to start with and the other one is iron 2 plus but there is some interaction going between them. So in certain time we find that electrons are actually exchange and this becomes iron 3 plus and this become iron 2 plus. So why it is happening? One electron it is getting exchanged between this iron plus 2 and iron plus 3. So they are getting exchanged so I can also have this interaction if there is a interaction going on between this and at the end what I am going to get that if they are exchanging fast it will be iron 2.5 plus iron 2.5 plus which shows that they are totally delocalized. Now over there I can have two different scenarios one is there delocalization happens however most of the time I can distinguish like which one is plus 3 which one is plus 2 then I will say it is a class 2 compound that means sometime this is iron plus 2 sometime this is iron plus 3 vice versa over here. So over here I can still say whether it is iron plus 3 or iron plus 2 I can still separate them but it is not stable they are exchanging but I can still find out it is plus 3 or plus 2 that will be class 2 but over here there can be a case over here like this where I found I cannot distinguish them right now indistinguishable I cannot separate whether it is a plus 3 or plus 2 because what I am going to get it is iron 2.5 plus it is totally delocalized and it is happening so fast that with our spectroscopic or any other experiment I am doing I cannot separate between plus 3 and plus 2 and that is going to be defined as the class 3 mixed valence compound. So class 1 is totally localized class 2 it is exchanging but I can still say it is plus 3 or plus 2. In totally localized it is remaining plus 3 it is remaining plus 3 the plus 2 actually retains its plus 2 state. In delocalized cases it will be changing plus 3 goes to plus 2 plus 2 becomes plus 3 but I can still find out whether it is a plus 3 or plus 2 I am not getting anything average value that is because the exchange of the electron is happening slowly so that it is slow compared to my spectroscopic measurement and I can find out what is the actual state over there that is the class 2 and class 3 is it is happening so fast I cannot distinguish it is becoming somewhere in the average value for an example 2.5 plus for iron indiscuous cases and that is defined as class 3 complex. So with that information in our mind let us go to an example where we are going to take a ferrocene kind of complex. So this is ferrocene now with this particular ferrocene what I am going to do is the following this is connected to a another CPD it is connected to the iron. So now you can see it is connected to two different ferrocene with this C-C bond. So that is why they are known as biferocene and not only that it also has a methyl ring over here methyl substituent. So that is the biferocene and now over there what I am saying one of them is in plus 2 state and one of them in plus 3 state. So overall charge is plus 2 plus plus 3 plus 5 each of the CPD give minus 1 charge so minus 4 so 1 charge positive charge is unbalanced that is given by this I3 minus anion. This is the structure of this biferocene molecule why I3 minus it is a large anion and it helped us to crystallize this. So we got this molecule and now my question is in this biferocene plus 2 and plus 3 and as we discussed in the earlier segment whether it is actually a class 2 kind of system or a class 3 kind of system whether I can distinguish them or I cannot. So this experiment I want to perform with this particular biferocene molecule and try to understand whether my molecule is having a mixed valence system such that I can distinguish or not it is a class 2 or class 3. So as we are discussing Mossberg spectroscopy we will take Mossberg spectra of this molecule and try to figure it out. So we did check the Mossberg spectroscopy percentage of transmittance velocity the respective y and x unit and we take this molecule and record the Mossberg spectra different temperatures first close to the room temperature system 287 Kelvin and we get only one set of data a doublet and then we slowly going to lower temperature. So from 287 we go to 270 and we found this peaks are getting broadened. So why it is getting broadened? Coming to from the next data that we record at 250 Kelvin where they started separating out this is we found at 250 Kelvin and then we go further down and then you get very well separated signals like this at when you reach 115 Kelvin. So why we are seeing such data? So first of all we found there are two different signatures first this particular signature and this one belongs to one particular system and the black one is for the other. So which is actually started separating from here the red one and which was also started try to separate from here and that is why it is getting broadened whereas the black one is remaining as it is or let me draw it in a other color for better understanding. So it is the green one so it is remaining there. So this is from the other part of the system and this was also present over here and the deconversion look like that but when they are combining together we got a very broad peak. So what is this green and the red signal? So what do I found that this green and red signal what they showcase is very interestingly their delta values are pretty similar. So the green and the red have very similar delta values but what is different is the delta EQ value. Green is much more separated whereas the red one is much more shrinked and getting our knowledge from the ferrocine ferrocinium system we then defined the red one the closely lying system is from the iron plus 3 whereas the well separated system it is from iron plus 2. So as you already know the ferrocine the iron plus 2 system is already well separated because of his higher electric field gradient that is why it is separated whereas the ferrocinium one it is actually much more shrink down and that is why they are close but previously when we discussed we said that the ferrocinium actually having electric field gradient almost close to 0 and that is why it is having a delta EQ value close to 0. But over here it has been having a very good EFG value over here and that is why we have this delta EQ that is because now I have electric field gradient non-zero and quite a significant unknown. Why this so? That is because over here look into the ferrocinial system one is actually only having methyl group one is connected to biferrocinium system and that is it is bringing some lattice electric field gradient which is non-zero in nature and that is making it a electric gradient which is significant and that is why we are seeing some value coming for this but this is actually saying it is a iron plus 3 system. Now what we can say about this at lower temperature you can say they are separable they are kind of localized so we can say it is a class 2 kind of system over here and as we move forward we go to class 3 at high temperature because you are not separable and we can say it is more of a iron 2.5 plus system where we cannot separate iron 2 plus and iron 3 plus and that is what is happening over here and over here MOSBA spectra can tell you which one is iron plus 3 which one is iron plus 2 and not only that it can also tell you when it is exchanging first so that you can get a distinguishable or indistinguishable system and that is one of the very nice example of MOSBA spectroscopy which can tell us what is actually happening in mixed balance kind of compound. So we will take more examples of that in the coming classes for this particular segment we will like to complete over here. Thank you. Thank you very much.