Ligands, Denticity & Chelating Agents | Coordination Compounds

[00:00:00]Hello friends, this video on coordination compound part five is brought to you by exam.com. No more fear from exam. So next term is the ligan which we uh want to discuss now. So the lians are the groups attached to the central metal ions. These are central metal ions. The groups directly attached to central metal ions in the complex are called lians. Okay. So lians can be negatively charged. For example, CN minus Cl minus C24 minus. Okay, it can be neutral. H2O NH3 CO. So it cannot be positive. It can be negative or neutral. It cannot be positive. And these generally donate electrons to central. Since they donate electron they are less is okay please note either they are negative charge or they are neutral. In case they are neutral they should have an uh lone pair of electron to donate. Okay. So we have small lians although we have large lians. These are small lians. We talk about the large lians. So we have for example NH2 CH2 CH2 CH2.

[00:01:36]So we have this is called one two di mean ethine. So we have long lians you know we have uh what do you call we have different kind of lians actually we'll talk about we have chilling lians they are they form chain kind of structure we have different type of lians we have in fact let's discuss lians now so we have different types of lians we have monodented lians we have bented liance we have tridented liance we have hexadented lians we have ambidented lians we have ched lians we have so many types of lians Mono dentate by give so many types we'll discuss this one by one as see this word dentate actually came from the Latin word dentist some the same word is dentist you know dentist came so this word dentist actually word tooth is the Latin and from the same word dentist came. So why this dented is used?

[00:02:47]Because this ligant they are thought of biting metal.

[00:03:05]Okay. At one or [Music] Okay. So just think from this perspective this dented means what?

[00:03:20]Tooth right the same word dentist this came dented. So dented mean tooth. So legend liance actually they have something to donate. This chlorine will donate lo of electron. This this guy will ammonia will donate lone pair of electron. It is expected that this ammonia is biting this cobalt.

[00:03:40]This chlorine is biting this cobalt.

[00:03:43]Okay. Now if this chlorine is biting cobalt at only one place it will be called monodentate or unidentate. Okay. So the definition is pretty easy.

[00:03:58]monodent if it has only one atom that can donate lone pair of electron because the legend the lians the basic definition of the liant is something which donates lone pair of electron to the so if central atom if particular lians only denotes only one pair of lone pair one lone pair that means it is biting the central atom only once so it is monodentic example can be ammon only once cl minus F minus water can only one don't oxygen CO is a mon fact to talk about the ions the negative charge liant the CL minus F minus okay example can be CH3 CO minus CN minus so these are my monodentate leads because they have only one place to bite the central atom or they have only one lone pair of electron to the next is by dentate lian. So these dented this liance has two donors. Example methylene diamine we just just now saw Ns2 CH2 CH2 N2 Okay. So here you see this nitrogen has none pair and this nitrogen has. So actually if there is one cobalt so this cobalt can be bitten by this nitrogen and this nitrogen. So from two place actually it can donate electron right. So the leg end which has two donor atom or it can donate electrons from two different atoms they are called by dented. The example can be CO minus B.

[00:06:03]Okay. So now this oxygen can donate electron this oxygen. So there is a nickel metal let's suppose. So nickel metal this oxygen can bite. This oxygen can bite. So two of these can bite this nickel. So it would be bent or dentate. Example here if you see this is my ethylene diamine. Let's suppose this is my nickel. This is a cobalt. Okay. This is my ethylene diamine. So this is my nitrogen. This is so you see this nitrogen is biting cobalt one and this nitrogen biting cobalt one. So overall this particular liant is biting the cobalt twice. Same thing here also if you see overall this particular liant is biting the cobalt twice. One from this nitrogen one from this. You talk about this let's suppose this is chlorine. This chlorine is biting cobalt only once. So this will be mono and this will be by your diet.

[00:07:19]Okay, this is one more example. The same thing actually but it is in a figure where you can actually see these values. There's a nitrogen here.

[00:07:29]This nitrogen including this nitrogen [Music] two. This is this is then we have tridented. Same concept. The lian which has three donor atoms that li will be tridented. Okay. The example can be diylene triamine. So just something like this CH2 CH2 here then CH2 CH2 [Music] N2 and N3. So if you see in this case there's a lone pair of electron here.

[00:08:23]There's a lone pair of electron here.

[00:08:26]So if you see there is one nickel for example. So here it can form bond. It can form bond. So one particular lian can bite this nickel from three place.

[00:08:39]Okay. So this trientate example in this case this nickel and you see this is one chain one I'll I'll make it in red.

[00:08:55]This is you see this particular whole thing is one liant right starting from here this whole thing is one liant and if you see this particular is biting nickel at one two and three places okay similarly we have hexadented so hexadented with the liant are the lians with six donor atoms. Example, if you see this is a metal and this whole thing what you see is one lian whole thing is one leg. You see this oxygen, this oxygen, this oxygen, this oxygen, this nitrogen and this. See how many atoms to donate electron? 1 2 3 4 5 6. There are six to donate electron and this is called E DA also used for purification of water called ethylene diamine tetra acetate. Remember this name this is pretty useful compound ethylene diamine tetra acetate. Okay. one particular metal and so many six sides in a given uh liance to donate electron is called hexad dented liance. One more unique type of liant is called mb dented. The moment you think of mb dented liant think of this word ambidextrous. And if you don't know then you can uh see your dictionary. This ambidextrous are the people who can write both from their left and right hand. So their left and right hand both work almost equally good. They are called ambidextrous people. So here also lians which can bind through two different atoms but at a given point of time they you'll write either from left to right. Right? You can't write from both hands. So example is this NO2. This NO2 if you see this nitro this NO2 can bond from nitrogen. NO2 let me draw NO2.

[00:11:24]This n2 it has two sides but at a given point of time since this is small right I mean these two cannot donate electron to the same metal same metal it cannot donate electron this is small other case we saw was like CH2 CH2 N2 here N2 here it was big so at a given point of time these two can donate electron both nitrogen can donate electron to nickel but in this case is small. So at a given point of time they both will not be able to donate electron. It will create more repulsion and it will be unstable and that is not possible. But at a given point of time sometimes nitrogen can donate sometimes oxygen can donate.

[00:12:08]So these type of lians which has ability to donate electron through two different sides of a lian but at a given point of time only one lian only one atom will donate electron and these are called MB dentate lians. Other example can be SCN for example sulf either you can get the electron from sulfur or from metal. This is a metal metal is bonded to sulfur in this case. In this case metal is bonded to metal. This is called thiocyinito. This is called isothiocinto. Please note this ambidented lian differs from bented liant. This is by dented lian where at a given point of time there are two sides from where you donate electron but ambient at a given point of time there's only one side but they have potential to donate electron from other side and with that you get different isomers. Example this is ambient right? In this case the nitrogen is donating electron to this cobalt. In this case oxygen is donating electron to this. This is bented. If you see at a given point of time there are two nitrogen molecules here and they both are directly electron to make. Correct? In bented liant there are two donor atoms and these two donor atoms can link simultaneously with the metals. But with ambidented lians only one donor atom can link with the central atom at a given point. And the reason I told you why because they are pretty big and two can actually donate electron but these are very small. Two of these uh two cannot actually donate electron. Okay. So that is about lians.

[00:13:55]In lians we also have don atoms. So the atom which actually directly attached to the central metal is called don atom.

[00:14:03]For example this particular lian has nitrogen oxygen both. So in this case the nitrogen is the don atom. In this case oxygen is the atom. In this case nitrogen is the atom because these are directly attached to central atom. So in this case is the central atom. In this case nickel is the central atom. So atoms of the liant that is directly attached to the metal is called donor. One more type of lians we have is called charting lians.

[00:14:34]Okay. So we have seen different type of lians till now. For example these are all ammonia. This is uniented. This is hexadented ed. We have seen this is bented dynamine and this is triented.

[00:14:53]So now I'm talking about the fact where I'm talking about D or poly that means D is B or Dhexa. So all these in this case right these case where I'm talking about D or polyented liance D hexans. So when these use more than two donor atoms to bind to a single metal ion it is called chilat liance. Okay. So when for example in this case this is using two donor atom.

[00:15:24]So this is called chilatic. This particular is using six donor atoms. One 2 3 4 5 6. This is called chilat. In this case this one 2 3 is used right. This is also called chilatling because they form a ring. They form a chilat complex and they're more stable.

[00:15:48]So this chilating agents they form more stable on this. This is unintented and if you see there is no uh chilat chilating ring actually here. So chilating agents are nothing but my lians the lians where poly d or poly lians they use more than two donor atoms to bind. For example, I have this uh poly this is bent for some reason I have a compound where it is forming only one bond with this is not so in that case it will not be a chilating agent only when the other is also used and forms a cyclic ring kind of structure it's called a chilatic agent right so chilating agent again is nothing but lians where I'm using bihixar neoly dented lians and making sure that more than two or more than two uh atoms of that liant are used to form the bond with the metal and thus it forms ring kind of structure and it is more stable than my uni-entered liant complex that is called shellacting agents okay so we have used this word dent a lot and with this there's a term called dentct CT that everything whatever we read till now bent and hexadent bite and poly dented all these things are grouped in this term called denticity. Okay. So density is what? Denticity is nothing but number of atoms of a single legend.

[00:17:33]Write here number of atom of single legend that binds to center. So for this ammonia density is one because one atom is bone. For this ammonia also density is one one all these density is one. In this case the density for this compound is six because six of these atoms for a given liant are for this liant for this liant density is two for this liant density is two for chlorine density is one chlorine density here also for this particular liant density is three and this other legant also densities.

[00:18:28]So this is for the given ligant. Okay. As I told why this word came dentist this this density word came in the Latin word dentist that means to and it is perceived that this liant is biting the metal at one more one or more than one linkage point. So if it is biting at one point it is called that is D1. It is biting at six point that is D6. Biting at two point density is two.

[00:18:59]Biting at one point again density is one. Whiting at three points density is three.

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