 Welcome you all to the MSP lecture series on advanced transformational chemistry. In my previous lecture I started discussion on coordination theory with a little bit of historical background and initiated discussion on Werner's coordination theory. So let me continue from where I had stopped with his systematic experimental work and conductivity measurement he established geometries for different coordination number I would say secondary valency and then he did not stop at this stage he went on further to isolate these compounds and in fact he isolated these compounds where you can see two ethylene diamine bidentate ligands are there and then these compounds showed optical properties and when again he presented his work Jorgensen argued with him and he ridiculed making any optically active compound without having a chiral carbon. So he firmly believed that in order to have an optically active compound there must be a chiral carbon. So he was more inclined towards organic chemistry understanding although he was an excellent experimental inorganic chemist of that time. However when he heard this kind of criticism Werner he took this as a challenge and he made this compound here you can see here he made this octahedral compound in this one there is no carbon ligand at all. So you have one the OH is there and ammonia is there he made this compound and he separated both the optical isomers D and L and then when it was shown eventually people started respecting Werner's coordination theory and of the establishment of optical activity of this compound without having a carbon and they started appreciating his theory and now people thought that coordination theory is complete and eventually he was given Nobel Prize in 1913. It is a very interesting molecule first of its kind you can see this is optically active compound of course later optically active compounds were made with tetrisethylene diamine and all those things but this one without having a carbon atom. Now let us come to the nomenclature of coordination compounds there are two systems for indicating the oxidation number of the metal the more commonly used system indicates the oxidation number in Roman numerals in parenthesis after the name of the metal or you can take the symbol and put superscript in the form of Arabic number with plus or minus denoting whether it is cation or anion for example chromium 2 plus cobalt 3 plus something also one can also use cobalt in the bracket Roman numerals indicating its oxidation state both are in the practice. The other system puts the charge of the coordination complex in Arabic number in parenthesis after the metal something like this something like this one can use or something like this one can use it appears to me this is more appropriate rather than writing like this and this should be used only when we are using a symbol and even when you are expanding any element like chromium then it should again come in Roman numerals in the bracket and here writing full name of an element and putting 2 plus as a superscript also does not look good this is a correct practice. So, using either system if the transmittal complex is negative in charge the name of the metal ends in 8. So, that means if we have an anionic complex the name of the metal pronounced at the end ending with the term 8 ok for example if you take this one this is anionic compound because platinum is in plus 2 state and diamine tetrachloroplatinate. So, in this one this is named as diamine tetrachloroplatinate. So, it is anionic if it is neutral or cationic compound then simply we should use the term the way it is for metals with Latin names the negative charge complex uses ferrate for example, when it is an anionic complex be for the following what the name we should use is given here for iron we should use ferrate for lead we should use plum bed for gold we should use orate and for silver we should argentate and for tin stannate and for copper cuprate and of course palladium palladate platinum platinate we use cobalt cobaltate iridium iridate. So, it continues like that the complete name of the complex must also indicate the presence of geometric isomers. Let us have a different ligands present on a metal and if that is the case and if there is a possibility of seeing more than one isomer then the name given should also indicate the type of isomer we are talking about. Then the prefixes such as cis trans meridional or facial should be included in the front of the complex when we write it. In addition stereo isomers also possible with tetrahedral and octahedral geometries in that case there is a possibility of optical isomerism then optical isomers also should be represented in the name by using prefixes something like this. So, one should use these symbols in front of optical isomers to denote there the nature of the isomer and if you have bridging ligands that bridges two metal centers one should use that are mu here and of course, when a ligand is bridging two metal centers it is obvious that minimum two are needed when the ligand acts as a bridging ligand in that one there is no need to put any subscript 2 here although if you put subscript 2 nothing wrong with it, but without subscript also one can write that indicates this ligand is bridging two metal centers. In case if the ligand is bridging three metal centers then mu 3 should be there where 3 is subscript ok. So, mu 3-1 we should write the complex formula and if we collating bidentate ligands are there in a complex then they have to be denoted using a prefix eta 2 and of course, eta 2 is not used now copper 2 is used eta 2 was earlier used for bidentate ligand making connection to the same metal and for a tridentate ligand making connection to the same metal is eta 3 or tetraidentate ligand all 4 donor atoms are binding to the same metal is called eta 4 and if 5 donor atoms are emerging from a ligand and going to the same metal then eta 5 etcetera for example, cyclopentadiene. So, when we have olefinic ligands eta simple makes sense because it mentions hapticity whereas, in other conventional ligands if they are bridging non-olefinic ligands it is better to use kappa rather than eta. Now let us look into isomerism and you know that isomers are nothing but compounds have the same formula, but different structures. So, again these isomers can be classified into two type of compounds one is structural isomers another one is stereo isomers. In the structural isomers we end up with lot of isomers here atoms have different connectivities that means, you can also have coordination isomers and linkage isomers and in the coordination isomers ligands and counter ions exchange places whereas, in linkage isomers ligand coordinates to metal in a different ways that means, you have a ligand having more than one type of donor atom in it in that case what happens one donor atom either of the donor atoms can bind resulting in linkage isomers. For example, if you take NO2 group either N can coordinate to the metal center or O can establish a link to the metal. So, nitrito or nitro we call them. Similarly, we come across the stereo isomers here atoms have the same connectivity, but different spatial arrangement stereo isomers atoms have the same connectivities, but different spatial arrangements are there. For example, M A2 B2 is there. In that case what happens 2A can be opposite to each other or of the same side. So, that results in geometric isomers that means ligands have different spatial arrangements about metal center. In that case we can have cis and trans geometry especially in case of square panner complexes and also in case of octahedral complexes when we have M A2 B2 in case of square panner complexes and M A4 B2 or M A2 B4 in case of octahedral complexes we come across cis and trans isomers whereas, in case of octahedral compounds when we have M A4 B2 or M A2 B4 we have cis and trans isomers. Similarly, when we have M A3 B3 we end up with having 2 isomers which are called facial and meridional in facial all the 3 ligands are in the same phase whereas, in meridional all are in different phase. Then if the compounds are non superimposable mirror images then we call them as optical isomers. I have given some examples for various isomerism. The first one is ionization isomerism you can see here in case of ionization isomerism what we have is a chloride is secondary valency and sulfate is primary valency whereas, in this one other isomer sulfate is secondary valency whereas, chloride is primary valency. In hydration we can have several isomers for example, you take first one hexa aqua cobalt 3 chloride and in this one 6 water molecules are secondary valency whereas, in this one the second one the composition is same we have 6 water molecules and 3 chlorides, but they change their positions. In this one 5 water molecules are inside the secondary valency and 1 chloride is there whereas, here we have 2 chlorides outside and water of hydration is there and in this case we have 4 water molecules are there inside and 2 chlorides are there, 1 chloride is primary valency and 2 water molecules are hydrated. So that means here it should be 4 read it as 4. Linkage isomerism as I mentioned when we have 2 donor atoms in a ligand either of them can bind at a time. So here in this one if the nitrogen is binded you can call nitro form and if the oxygen is binded O form you can O nitrite, nitrito or N nitro. So one can mention like this. So you have linkage isomerism we also come across linkage isomerism in case of NCS where N can either coordinate to the metal or S can coordinate to the metal and coordination isomerism. So here if you see we have 1 cation and 1 anion and if you just look into the ratio 1 platinum and 1 thaladium is there and 4 ammonium and 4 chlorides are there and the composition remains same in these complexes. But here cation is a platinum compound and anion is a palladium compound whereas here palladium is a cationic compound and platinum is an anion compound. So this is coordination isomerism and similarly we come across in case of octahedral compounds also. We have hexamine cobalt 3 plus a cation and hexasinochromate as an counter anion whereas here hexamine chromium 3 plus is a cation whereas here hexasino cobaltate is the anion. So they are coordination isomers and coordination position isomers will come into picture where we can see cobalt 3 is here and cobalt 4 is there and cobalt 4 is here and cobalt 3 is here. Rest remains more or less same or there may be some change depending upon the change of axis state anion ligands may take different positions. So this is called coordination position isomerism. Then coordination polymerism again here we consider this diamino dichloroplatidum. So if you just look into it 1 platinum 2 amine 2 chlorides composition is 1 is to 2 is to 2 and now we have a combination of cationic and anionic compounds here and again if you say 2 metals are there and 4 ammonium 4 chloride means again the composition remains same. This is coordination polymerism and same thing is observed in rest of these complexes as well. And then conformation isomerism. Conformation isomerism can be seen actually in the case of nickel D8 system some compounds can exist in tetrahedral geometry and the same compound can exist in square planar geometry. For example, if you take di bromo this di phenyl ethyl phosphine complex this can show both square planar and tetrahedral geometry. So dark brown diamagnetic square planar and the dark green paramagnetic tetrahedral. So this is called conformation isomerism and summation isomerism here you can see the number of constituent ligands remains same the composition remains same and if you take here we have taken the bromo ethylamine we are taking chloro ethylamine but when bromo is there chloride is in secondary valency when chloro amine is there bromide is secondary valency that means this is called summation isomerism and the ligand isomerism is there in case of ligand isomerism you can take like normal propyl amine is there and here isopropyl amine is there. So in this case what happens you see ligand isomerism is there and valence isomerism was proposed by Jonathan in 1955 he was one of the students of Jorgensen and here you can see the valence isomerism here valency varies in this one and then spin isomerism is also shown in complexes wherever the magnetism is temperature dependent or sometime what happens with temperature high spin complex become low spin complex and low spin complex become high spin complex when it is cooled this is called spin isomerism that means we have a several isomerization process is there and some examples are there in each case when we go to polydentate ligands a typical example is ethylene diamine both the amines of the ligand can bind to the same metal forming a ring. So this is called chelate ring and then many polydentate ligands having longer chain capable of donating all the donor atoms binding or establishing bond with the donor atoms to the same metal then they are called chelate ligands and such compounds are called chelate compounds or chelate complexes. A typical example for polydentate ligand is this hexadentate ligand EDTA, EDTA abruation expansion is ethylene diamine tetracitic acid and then if it is anionic then it is called tetracite so you can see EDTA 4 minus and here two nitrogen are there and four carboxylate oxygens will be establishing and it forms stable complexes with most of the transients elements and also some of the main group elements. So EDTA can wrap around a metal ion to coordinate at six coordination sites ligands that bind to more than one site are called chelating ligands and linkage isomerism I had mentioned for example if you take this NO2 minus when it is binding by oxygen we call nitrito so that means the moment the ligands name is pronounced as nitrito you should assume that in this one in NO2 oxygen is connected to the metal ion and not nitrogen and when the nitrogen is coordinated simply use the term nitro that indicates is the n that is coordinating to metal not the either oxygen atoms and linkage isomerism and involve ligands that may bond via different sites again I showed you in the previous slide that I have written the structures here and also interesting thing is these compounds have different properties and also colors you can see when nitro is there where nitrogen is coordinated it is orange yellow in color and in this one it is orange red or something like that and stereo isomerism stereo isomers have the same connectivities but different spatial arrangements in geometric isomers the ligands have different spatial arrangements about the metal ion optical isomers are compounds with not superimposable mirror images they come under stereo isomerism and geometric isomerism geometric isomers differ in the geometric arrangement of the ligands around the central metal as I mentioned for example you consider this diamino dichloroplatinum when two amines are cis to each other we call it cisplatin and when they are trans to each other we call that transplatin so that means this compound exhibit geometric isomerism and cis and trans compounds can be separated or they can be prepared using different methods and of course very nicely trans effect was used again Werner used a trans effect to make these isomers in their pure form starting from appropriate metal complexes in one case he used a tetra ammonium platinum compound he used in another case he used tetrachloroplatinate he used. I shall tell you about trans effect and preparation of different isomers using trans effect at later stage and optical isomers octahedral complexes containing polydentate ligands can also form optical isomers complexes with 3 rings 3 by dentate ligands for example ethylene diamine is there in this compound 3 ethylene diamines are having bound to cobalt in generating tris ethylene diamine cobalt 3 plus compound so it can be viewed like a propeller with 3 blades the structure can be either left or right handed with non superimposable mirror images I have shown here something like this then the right handed isomer requires going clockwise to get from the upper triangle to the lower triangle so that means if you start tilting this one basically what happens it comes to this one the prefix for this isomer is given as del something like this you should remember that right handed isomer you just take this one and do clockwise rotation one rotation and then you will end up with this one so in that case what happens you should give a prefix del on the other hand a left handed isomer requires going counter clockwise to get from the upper triangle to the lower one for example instead of doing clockwise rotation perform anticlockwise rotation and then for this one the prefix for this isomer is del so this is how you can distinguish between two optical isomers among coordination compounds and this is a typical octahedral compound let us look into some isomers cobalt 3 when it is treated with ethylene diamine it can react in a different form and several products can be formed one such compound having two ethylene diamine two chloride in the secondary valence is violet and the trans isomer is green so that means when you are making this one obviously says there is a possibility of formation of trans compound and the trans compound is green whereas cis compound is violet when you are using excess of ethylene diamine the reaction also results in the formation of a yellow product having this composition where we have this ethylene diamine cobalt 3 plus so if I ask you to rate all possible isomers in this reaction you should be able to rate all possible so determine the number of isomers of each of the products label any enantiomer with the proper prefix either this or that one whether you make clockwise or anti clockwise rotation. So first one is the yellow product is this one it is ethylene diamine so of course once when you write this one you will come to know that there is a possibility of writing another not superimposable mirror image of this one so we have this one so these two are that means this one gives two isomers and besides giving one geometric isomer and this one of them can be geometric isomer as well and then when you go for this one having two ethylene diamine two chloride there is a possibility of having two isomers here so one trans isomer one cis isomer and cis isomer can also exhibit optical isomerism having non superimposed mirror image something like this so that means the violet product consists of a pair of optical isomers and then the green product is non-optically active because it has a mirror plane so that means we have one two three isomers are there and with tris ethylene diamine we have two more isomers so totally when you interact cobalt three chloride with ethylene diamine there is a possibility of making five isomers. So before I conclude this lecture let me bring to your attention the nomenclature of coordination compounds once again you should remember these things and one thing you should remember now irrespective of earlier convention was irrespective of we used to name anionic ligands first neutral ligands second and then cationic ligands at the end and then we used to bring the name of the metal so now the convention is irrespective of the nature of the ligands we should use only alphabetical order alphabetical order should be used while pronouncing or naming a complex if ionic the positive ion is named first then the negative ion you should remember if the ionic complex if complex is ionic and if it is cationic the positive ion is named first and then the negative ion at the end and then the inner coordination sphere is indicated by square brackets while writing we should remember in the formula the metal is written first followed by the ligands and here doesn't matter where we write in alphabetical order or not doesn't matter but matter should be written first in the square bracket followed by the ligands in naming the ligands are named first then the metal in naming the ligands are named first in alphabetical order irrespective of the nature of the ligands and then the metal if the ligand itself contains a prefix in its name say dimethylamine or triphenyl phosphine then again if more than one is there so then to avoid confusion we should use a different kind of prefix to indicate the number of ligands and also number of such atoms present or group present in the ligand itself and the ligand name is placed in parenthesis for example dimethylamine is there in that case if two ligands are there in the coordination sphere then it rather look odd to say dimethylamine instead you should say bis dimethylamine so that means appropriate prefix should be used for them for example for two instead of die use bis and for three instead of using tri use trees and then for four use tetra instead of tetra use tetra keys for five use pentakis or six hexakis seven heptakis eight octakis nine nonakis and ten deacakis so ligands are listed in alphabetical order ignoring any prefix okay I should remember irrespective of how many ligands are there the first letter of the ligand should be considered while labeling them or naming them in alphabetical order if aqua and amine ligands are there no matter how many aqua ligands water ligands are there and how many ammonia are there irrespective of that one the one that comes first is aqua and then m so first ammonia should come and then aqua should come so this is how it should be named and while naming while considering the alphabetical order ignore any prefixes that indicates the number of ligands present most ligands have special names with all negatively charged ligands ending in the letter o for example chlorobromo iodo something like that the most neutral ligands retain their usual names except ammonia okay for example ammonia we call amine and water we call aqua and co we call carbonyl so name of common ligands I have listed here bromocarbonato chlorosino so H-hydrido OH-hydroxo and O2 oxo some examples have shown here to make you familiar with naming here you can see dichloro tetramine cobalt 3 chloride and here if you take monochloro or you can say monochloro or simply chloro is also monochloro or chloro is fine there is no need to indicate when we write chloro it obviously indicates that there is only one chloride is there so no need to put monochloro pentamine cobalt 3 chloride and here this is a fissure salt potassium hexa nitro nitrito cobalt 8 nitrito means you should know the donor atom that is binding to the metal center and here in this one dichlorotriamine platinum 2 tetrachloroplatinate 2 so you have to see tetrachloroplygen anionic complex should come later and in this one magnus green salt tetramine platinum 2 and then tetrachloroplatinate minus so this one similarly you can name these things and you can practice let me stop at this juncture continue talking about more interesting facts about coordination compounds in my next lecture until that have a wonderful time in reading and understanding chemistry.