Coordination Isomers

Concept: Structural Isomerism

10m
Video Transcript

Hey guys in this new video we're going to take a look at all the different types of structural isomers that are allowed with coordination compounds. So, we're going to say first of all that isomers are compounds that possess the same molecular formula, which means they have the same exact atoms but they differ their location of each atoms. So, they're connected in special ways. So, isomers same formula but different structures. So, here we can organize it into different groups. So, if we're talking about isomers that have different connections, they're connected differently then we refer to them as constitutional isomers, for those of you who go into organic chemistry we'll take a more in-depth look at what we call constitutional isomers. Now, constitutional isomers fall into two categories, we have our coordination isomers and then we have our linkage isomers. So, we're going to say coordination isomers, this is ligand and or counter ion swapping. So, what does that mean? basically, we're going to say coordination isomers is when the composition of the complex ion changes but not the compound overall. So basically, one example is when we have a looking and encounter ion changing positions, for example, I could have platinum here, it's connected to four amines, two chlorines and then we have a counter ion out here, NO2. So, coordination isomers means I switch the positions of one of the ligands and the counter ion. So, one of these ligands I'll switch out on the chlorines with the counter ion, okay? So, now if we look my Cl ligand is now a counter ion and my NO2 counter ion is now a ligand, these will represent coordination isomers, we've swapped the ligands and our counter ions, also another way of thinking about this is if you're swapping different ligands. So, for example. So, we can continue downward here. So, another example of a coordination isomer is when ligands switch positions. So, we have chromium connected to the amine ion six of them, this is a positive counter ion, it's connected to a negative counter ion. Now, what happens I can switch the ligands, this ligand can switch places with this ligand. So now, here we're going to say CR is now with cyano and cobalt now is now with the amine group, okay? So, remember coordination isomers mean we can swap either the ligand with the counter ion or we can switch ligands, these both represent two different examples of coordination isomers.

 

Now, linkage isomers are different, this is just difference in donor atom. So basically, we're saying here, this is just the ligands attaching in different ways in different ways, for example, let's think for example a thiocyanate S, CN, right? So, we have thiocyanate here. Now, remember thiocyanate, this is a monodentate ligand, meaning that it only has one atom that can donate but here's the thing, it can either be the sulfur donating or it could be the nitrogen donating its lone pair to the central metal cation. So, what I think of is I could say I have cobalt here, connected to SCN, okay? So, we can say that. So, in this example the way I've written it it's the S with its lone pair that's connecting to my Cobalt or I can write it in a different way, I can write it NCS like that, in this example it is the nitrogen now with its long tail connecting to the cobalt. So, linkage isomers just means to put a link on the ligand links in a different way. So, that's if we have different connections, if we have the same connections then they referred to as stereo isomers. Now here, this is when they have stereo centers versus when they don't have stereo centers, we're going to say stereo centers are also referred to as chiral centers a chiral Center is when you have an element connected to four different groups, for those of you who haven't watched my organic chemistry chapter yet, probably a good idea to take a quick look at that, to take a look at chiral compounds, chirality, that's just when an element is connected to four different groups. Now here, if you have a chiral Center than your optical isomers, that just means you have a ligand connected to four different things. So, maybe it's connected to a chlorine a bromine an amine and a water and so that would be a chiral molecule because the Cobalt connected to four different groups, okay? And in here, enantiomers they're just mirror images of each other. So, pretend there's a mirror here and then this thing is looking into the mirror, what is it sees back, it sees back it's reflection, its mirror image, okay? So, these guys here, the relationship together will be enantiomers then finally, if you don't have a chiral Center, we refer to you as geometric isomers, this is when we're talking about cis and trans isomers also called the diastereomers. So, for example, I could have PT NH3 2 Br2. So, we say that here, the, the central metal is connected to four ligands two amines and then two bromines. So, here I can write it as cis or trans, what exactly does that mean? cis would just means that the Platinum the 2Br's are on the same psi together and the 2 NH3's are on the same psi together. So, this will be my cis configuration, trans is when they're opposite of each other. So, one Br is up here, the other Br is down here, one NH3 is up here, the other NH3 is down here. So, this would be my trans configuration I could also have another example where I have, let's say, we use copper, it is connected to four waters and two fluorines. So remember, this is octahedral because it's connected to six ligands so the copper could be in the center, we could have the two fluorines be trans to each other, one is on the top ones on the bottom. and then remember we in with octahedral shapes we have these four on the same plane with each other. So, this would be trans, I could also write it as cis, coppers in the center, okay? And I could have those two fluorines on the same plane with each other. So, now they're cis and I still have the four waters involved as well. So, these are the different types of isomers that are allowed when it comes to different types of coordination compounds, again you're just getting a taste of what isomers are, when you get to organic chemistry you're going in greater detail and it comes to constitutional isomers in the different types of categorizations that exist in organic chemistry for them, we also talk in greater detail about stereo isomers, for right now we're going over the simplest versions of these and how they relate to the coordination compounds. So, take note of what we covered here, remember the different types of examples that we talked about to classify these different categories, it's essential to knowing how to identify different groups.