The glycinate anion, gly-= NH₂CH₂CO₂ ^-, bonds to metal ions through the N atom and one of the O atoms. Using to represent gly-, sketch the structures of the four stereoisomers of Co(gly)₃.

Video transcript

Hi, everyone. Let's look at our next problem. It says the two dietert butty phosphene ethane violate anion. Thankfully abbreviated capital P, capital S lowercase TB U minus is a bent ligand. It bonds the metal metal center ion using one P atom and one S atom draw the structures of the four stereo isomers of the complex ion. It's an ion with iron in the center and three of these PST pu ligands use the following to represent PST B minus. And we have a capital P capital S with a semi circular arc linking them representing the rest of the molecule. So the key information is just that we have a phosphate and a sulfur, they're linked in a Biodent ligand and each of them bonds to the central metal ion. So we know we have three of our PST B ligands multiplied by two bonds, pliant. So we have six bonds total, which means we have an octahedral geometry. So, very fortunately, we have a little help from our problem because when we think about octahedral geometries, especially with linked ligands like this, and we're not talking about something straightforward like mono dentate ligands uh in an arrangement of four and two or five and one. It can be a little daunting to sit there and try and contemplate all the different isomers, rotate them around, try and determine if they're the same. But our problem tells us right out that we will have four ster isomers. So if we get to four, we can sort of logically arrive at them. We know we've done enough and we don't have to keep on contemplating all of these iterations and rotations. So that definitely helps us here. So let's start drawing. So we'll start with an iron atom with six bonds in their octahedral arrangement. And let's just fill in three of our P STV U ligands. So I'll start at the top with a phosphorus and then put a sulfur, they have to be next to each other 90 degrees apart and then connect them with an arc. And now I'm just going to go around the outside of my molecule, alternating P and S connecting each pair with an arc. So there I go, I have my three by dentate ligands. So one isomer down. Now, the first step I'm going to do is draw a mirror image because often we have pairs of an anti ier and then I'll check is that a superimposable mirror image or does that represent two separate molecules? So let's draw the mirror image of this molecule. So we have our mirror image and now we need to determine if they're super imposable when we start getting into three dimensional geometry like this, where we have an arrangement that kind of looks like blades of a propeller. It can be really tricky just to look at this in a two dimensional drawing and see whether they would overlap. So often, the best thing to do is manually draw the flipped over a rotated version of your first structure to see if it matches your second structure. So I'm going to draw in red, the rotated version of my first molecule. So I'm just gonna imagine rotating at 180 degrees or as if I sort of flipped the whole thing over and I'll draw on red. So the easiest thing to start with is of course my iron and then the top and bottom atom, since that's sort of my axis of rotation, they'll remain the same and now rotate the whole thing 180 degrees. Well, it's pretty obvious to see right away that this is not going to make the same molecule because when I flip it over my phosphorus atoms which were in the front of my square plane are now on the bonds that project behind the screen and the sulfur atoms are in the front. So it's, we'll check with looking at our links between the two atoms of each ligand. But it's, you know, pretty clear right away that this isn't going to be the same. So we know our top phosphorus was linked to a sulfur atom in the back left, which is now in the front, right. So draw that little bond, we had a sulfur and phosphorus that were on the left side of the square plane that now rotated around or on the right side of the square plane linked together. And finally, our sulfur atom that was on the bottom and was linked to the phosphorus in the front, right is now linked to the phosphorus in the back. Left, draw that in. But we can see quite clearly looking at these two molecules are rotation are rotated first molecule and the mirror image of the first molecule, we can try and move this around to match up the phosphorous and sulfur. But every time we do the linkages of the between the P and S are going to be in the wrong place. So we now have two isomers in blue here on the top row, they're a pair of an ante that are not superimposable. So now let's think about what would be a way to change our molecule to create another isomer. Well, if we go back to our original molecule or our original isomer and I just filled in those PS and s's going around in a clockwise direction. Now let's just switch the phosphorus and sulfur in each case. So I'll start with a sulfur on the top and then move to the right and put a phosphorus and link them together and in each case, just swap the sulfur and phosphorus and it can take a little bit. But when you practice rotating this around, you'll see that it doesn't, there's no way to make it match up with either of our two previous isomers by rotating it around. So we've got a third one and our logical possibility for the fourth would be the mirror image of this one. So we have that mirror image And once again, let's rotate around the third isomer we drew and make sure it's not super imposable. But as you can guess by the fact that it's a similar structure to our other isomers, we're going to have the same issue when we rotate it around Sulfurs end up in the back boss versus in the front top and bottom, stay the same. And there's no way to superimpose this on our mirror image, not super imposable. So right there we have another pair of an anti emmers, non superimposable mirror images. And here we go, we have four ster isomers which we know is all we can have. So we know we have found all of the ones we're supposed to draw. So two pairs of an anti MERS and we arrived at the two different uh ditherers by switching the sulfur and phosphorus in each ligand. See you in the next video.