1 00:00:00 --> 00:00:01 2 00:00:01 --> 00:00:02 The following content is provided under a Creative 3 00:00:02 --> 00:00:03 Commons license. 4 00:00:03 --> 00:00:06 Your support will help MIT OpenCourseWare continue to 5 00:00:06 --> 00:00:10 offer high-quality educational resources for free. 6 00:00:10 --> 00:00:13 To make a donation or view additional materials from 7 00:00:13 --> 00:00:15 hundreds of MIT courses, visit MIT OpenCourseWare 8 00:00:15 --> 00:00:17 at ocw.mit.edu. 9 00:00:17 --> 00:00:25 PROFESSOR: OK, we have the clicker question up. 10 00:00:25 --> 00:00:28 We're going to have another clicker competition today. 11 00:00:28 --> 00:00:37 The defending champs, there's Darcy's recitation. 12 00:00:37 --> 00:01:44 So, OK, let's just take 10 more seconds on this. 13 00:01:44 --> 00:01:50 OK, not too bad, 74%. 14 00:01:50 --> 00:01:53 So, in this problem, the trick was just to look at the 15 00:01:53 --> 00:01:58 equation and figure out what's going on -- which element is 16 00:01:58 --> 00:02:01 being reduced, and which one is being oxidized. 17 00:02:01 --> 00:02:04 So this is something that you will be seeing on 18 00:02:04 --> 00:02:06 the upcoming exam. 19 00:02:06 --> 00:02:09 So we're going to talk about that in a few minutes, but 20 00:02:09 --> 00:02:13 first I want to answer the question from last time. 21 00:02:13 --> 00:02:18 So, first, let's just, I know you've all been wondering 22 00:02:18 --> 00:02:26 about how vitamin B12 is reduced in the body. 23 00:02:26 --> 00:02:28 So, let's take a look at this now. 24 00:02:28 --> 00:02:38 So, if everyone can quiet down, let's get started. 25 00:02:38 --> 00:02:42 So, vitamin B12 is reduced by a protein that's 26 00:02:42 --> 00:02:43 called flavodoxin. 27 00:02:43 --> 00:02:46 And flavodoxin is a protein that has a cofactor which is 28 00:02:46 --> 00:02:53 a flavin, and that's also a vitamin B, as it turns out, 29 00:02:53 --> 00:02:56 they're both vitamin B's. 30 00:02:56 --> 00:03:03 So, vitamin B12 has a redox potential or a standard 31 00:03:03 --> 00:03:05 reduction potential of minus 0 . 32 00:03:05 --> 00:03:11 5 2 6 volts, and that is a very low number for 33 00:03:11 --> 00:03:13 a biological system. 34 00:03:13 --> 00:03:16 And flavodoxin has a potential of minus 0. 35 00:03:16 --> 00:03:19 2 3 volts. 36 00:03:19 --> 00:03:31 So, which of these things is a better reducing agent? 37 00:03:31 --> 00:03:34 So, which thing, you want to think about reducing agent, 38 00:03:34 --> 00:03:37 which thing would prefer to be oxidized and reduce 39 00:03:37 --> 00:03:42 something else? 40 00:03:42 --> 00:03:46 So, with the low negative number, B12 is a better 41 00:03:46 --> 00:03:50 reducing agent than flavodoxin, and just based on these 42 00:03:50 --> 00:03:54 numbers, vitamin B12 should be reducing flavodoxin, not 43 00:03:54 --> 00:03:58 the other way around. 44 00:03:58 --> 00:04:01 So, how does this work then? 45 00:04:01 --> 00:04:06 So, in your body right now, you have a version of a flavodoxin 46 00:04:06 --> 00:04:10 protein, and you of vitamin B12 attached to an enzyme, 47 00:04:10 --> 00:04:14 methionine synthase, and for that to be activated, it 48 00:04:14 --> 00:04:15 needs to be reduced. 49 00:04:15 --> 00:04:18 So how is this happening? 50 00:04:18 --> 00:04:23 So, let's consider whether the reduction of B12 by 51 00:04:23 --> 00:04:25 flavodoxin is spontaneous. 52 00:04:25 --> 00:04:27 It happens in your body so one might think that it is. 53 00:04:27 --> 00:04:30 But let's look at that. 54 00:04:30 --> 00:04:33 So, we can look at it the same way you've looked at all the 55 00:04:33 --> 00:04:38 other systems, we're talking about batteries, electric 56 00:04:38 --> 00:04:42 chemical cells -- you can use the same equations if it's 57 00:04:42 --> 00:04:45 a biological system as you can for any other system. 58 00:04:45 --> 00:04:47 So we've seen this equation before. 59 00:04:47 --> 00:04:51 We've calculated changes in the standard reduction potential 60 00:04:51 --> 00:04:55 for a cell, and we talked about e nought for reduction minus 61 00:04:55 --> 00:05:01 the e nought for oxidation, and we can use that same equation. 62 00:05:01 --> 00:05:04 So we can put it in in the biological context. 63 00:05:04 --> 00:05:07 The vitamin B12 is the thing that's being reduced, and the 64 00:05:07 --> 00:05:11 flavodoxin is the thing that's being oxidized, that's the 65 00:05:11 --> 00:05:12 reaction that happens. 66 00:05:12 --> 00:05:16 So, we can plug those values in. 67 00:05:16 --> 00:05:18 So we have minus 0 . 68 00:05:18 --> 00:05:21 5 2 6 volts, minus a negative 0 . 69 00:05:21 --> 00:05:26 2 3 volts, and if you put those together, you get minus 0 . 70 00:05:26 --> 00:05:29 2 9 6 volts. 71 00:05:29 --> 00:05:34 So is that going to be a spontaneous reaction? 72 00:05:34 --> 00:05:36 No, it's not going to be. 73 00:05:36 --> 00:05:39 Your value for the e is negative, which means what 74 00:05:39 --> 00:05:43 is true about delta g? 75 00:05:43 --> 00:05:47 Positive, so it won't be spontaneous. 76 00:05:47 --> 00:05:52 So, let's figure out how not spontaneous it's going to be. 77 00:05:52 --> 00:05:54 How much trouble are we all in? 78 00:05:54 --> 00:05:58 So we can use again, the same equation that we used for 79 00:05:58 --> 00:06:01 batteries that we've used in this course -- just because 80 00:06:01 --> 00:06:02 it's a biological system, doesn't mean the 81 00:06:02 --> 00:06:04 equation doesn't hold. 82 00:06:04 --> 00:06:08 So our equation for delta g nought minus n, the number of 83 00:06:08 --> 00:06:11 moles of electrons times Faraday's constant times 84 00:06:11 --> 00:06:15 the change in the standard potential. 85 00:06:15 --> 00:06:16 So we can plug it in. 86 00:06:16 --> 00:06:19 I can tell you it's a one electron process -- flavodoxin 87 00:06:19 --> 00:06:23 puts one electron into vitamin B12, so we have minus 1 times 88 00:06:23 --> 00:06:26 Faraday's constant times the cell potential difference 89 00:06:26 --> 00:06:29 you just measured, which is minus 0 . 90 00:06:29 --> 00:06:35 2 9 6, and if you multiply those out, then you get 28 . 91 00:06:35 --> 00:06:38 6 kilojoules per mole positive. 92 00:06:38 --> 00:06:41 That is a very big value -- that's not spontaneous and 93 00:06:41 --> 00:06:46 it's not a small number for a biological system. 94 00:06:46 --> 00:06:49 So, why don't we all have heart disease and 95 00:06:49 --> 00:06:49 megaloblastic anemia? 96 00:06:49 --> 00:06:53 Those are problems associated when this particular 97 00:06:53 --> 00:06:58 enzyme is not functioning. 98 00:06:58 --> 00:07:01 So, what happens in this system is what happens in a number 99 00:07:01 --> 00:07:03 of biological systems. 100 00:07:03 --> 00:07:06 How do you drive something forward that is 101 00:07:06 --> 00:07:07 not spontaneous? 102 00:07:07 --> 00:07:11 And what you can do is put energy into the system to drive 103 00:07:11 --> 00:07:14 that non-spontaneous reaction. 104 00:07:14 --> 00:07:17 And in this case, the energy that's put into the system is 105 00:07:17 --> 00:07:18 from a molecule called s adenosylmethionine. 106 00:07:18 --> 00:07:22 And the cleavage of s adenosylmethionine has a delta 107 00:07:22 --> 00:07:28 g nought of negative 37 . 108 00:07:28 --> 00:07:30 6 kilojoules per mole. 109 00:07:30 --> 00:07:34 So it's more favorable than the reduction of B12 is 110 00:07:34 --> 00:07:38 unfavorable, and so this drives this system. 111 00:07:38 --> 00:07:43 So, s adenosylmethionine is your friend, it helps in the 112 00:07:43 --> 00:07:46 body for B12 to be reduced so that you can function 113 00:07:46 --> 00:07:49 and be healthy. 114 00:07:49 --> 00:07:52 So, many biological systems work like this. 115 00:07:52 --> 00:07:56 So what have we been calling something, a cell, in which an 116 00:07:56 --> 00:08:00 unfavorable reaction is driven by applying some kind of energy 117 00:08:00 --> 00:08:11 or current, what do we call that? 118 00:08:11 --> 00:08:13 Two types of cells we mentioned. 119 00:08:13 --> 00:08:18 One that has a favorable, it has a spontaneous reaction. 120 00:08:18 --> 00:08:22 A cell that has a spontaneous reaction is called what? 121 00:08:22 --> 00:08:22 Galvanic. 122 00:08:22 --> 00:08:26 And the other kind is called? 123 00:08:26 --> 00:08:27 Yup. 124 00:08:27 --> 00:08:28 So, electrolitic cell. 125 00:08:28 --> 00:08:30 So this is sort of the biological equivalent of an 126 00:08:30 --> 00:08:33 electrolitic cell where you have s adenosylmethionine 127 00:08:33 --> 00:08:37 cleavage coupled to an unfavorable reaction to 128 00:08:37 --> 00:08:41 drive that reduction of B12 by flavodoxin. 129 00:08:41 --> 00:08:44 And B12 has such a low potential, that there 130 00:08:44 --> 00:08:47 really isn't anything else that can reduce it. 131 00:08:47 --> 00:08:49 It has one of the lowest potentials known in a 132 00:08:49 --> 00:08:53 biological system, so nature said, OK, well, we're not going 133 00:08:53 --> 00:08:56 to make something with a lower potential to do this chemistry, 134 00:08:56 --> 00:08:59 we'll have something else with a higher potential, but will 135 00:08:59 --> 00:09:03 drive the reaction because it's going to be non-spontaneous. 136 00:09:03 --> 00:09:07 So that's how this works. 137 00:09:07 --> 00:09:10 So, today there's a long list of topics, all of these are 138 00:09:10 --> 00:09:14 pretty short and basically constitute the introductory 139 00:09:14 --> 00:09:16 material in this unit. 140 00:09:16 --> 00:09:21 And we've jumped ahead, this is in chapter 16. 141 00:09:21 --> 00:09:26 So, I really like transition metals, because I am a fan of 142 00:09:26 --> 00:09:30 metals that are involved in biological systems. 143 00:09:30 --> 00:09:35 So, I just thought as part of chemistry, I just want to sort 144 00:09:35 --> 00:09:38 of review the kind of basic areas of chemistry 145 00:09:38 --> 00:09:39 for a minute. 146 00:09:39 --> 00:09:41 This is not in your handout, but just so you sort of 147 00:09:41 --> 00:09:45 think about what are all parts of chemistry. 148 00:09:45 --> 00:09:49 There is organic chemistry -- does anyone know what organic 149 00:09:49 --> 00:09:52 chemistry concerns itself with? 150 00:09:52 --> 00:09:56 Carbon. 151 00:09:56 --> 00:10:02 And then what we have known as inorganic chemistry. 152 00:10:02 --> 00:10:07 Anyone know what that is? 153 00:10:07 --> 00:10:11 Not carbon. 154 00:10:11 --> 00:10:14 So, a lot of people who are inorganic chemists study 155 00:10:14 --> 00:10:18 transition metals, but it's basically other things 156 00:10:18 --> 00:10:20 besides carbon. 157 00:10:20 --> 00:10:25 And then one of the areas that I like is bioinorganic 158 00:10:25 --> 00:10:31 chemistry, and these are people who study metals in biology. 159 00:10:31 --> 00:10:40 So, people who study metals in biology, and we're also kind of 160 00:10:40 --> 00:10:46 referred to as, we're sort of in a club, which 161 00:10:46 --> 00:10:50 we call the MIB. 162 00:10:50 --> 00:10:53 So, some of you -- and Will Smith did a disservice -- 163 00:10:53 --> 00:10:58 people now associate this with hunting aliens, but in fact, 164 00:10:58 --> 00:11:02 people who are in MIB are associated with hunting for 165 00:11:02 --> 00:11:04 metal ions in biological cells. 166 00:11:04 --> 00:11:09 So this is sort of the true MIB. 167 00:11:09 --> 00:11:12 And in an honor of this discussion today, I am 168 00:11:12 --> 00:11:14 wearing a teeshirt from one of our meetings. 169 00:11:14 --> 00:11:18 This is from the International Congress on Bioinorganic 170 00:11:18 --> 00:11:22 Chemistry, which we refer to as ICBIC. 171 00:11:22 --> 00:11:26 And you notice that the clever people who made this teeshirt 172 00:11:26 --> 00:11:31 used the B from the bioinorganic to make B12, which 173 00:11:31 --> 00:11:38 is a very popular vitamin in the bioinorganic community. 174 00:11:38 --> 00:11:42 So, metals in biology. 175 00:11:42 --> 00:11:46 Carbon, carbon's a good thing, amino acids are 176 00:11:46 --> 00:11:48 good, I like proteins. 177 00:11:48 --> 00:11:51 But often, when you take a metal and attach it to a 178 00:11:51 --> 00:11:55 protein, that protein can do really cool chemistry -- 179 00:11:55 --> 00:11:58 really need oxidation reduction chemistry. 180 00:11:58 --> 00:12:02 So, here is part of the periodic table that includes 181 00:12:02 --> 00:12:04 many of these transition metals that we're going 182 00:12:04 --> 00:12:06 to be talking about. 183 00:12:06 --> 00:12:10 And things that are in orange here are metals that are very 184 00:12:10 --> 00:12:12 important biologically. 185 00:12:12 --> 00:12:15 Some of the things that are in grey here are metals that are 186 00:12:15 --> 00:12:20 used as probes or as drugs in biological systems, and 187 00:12:20 --> 00:12:22 some could be both. 188 00:12:22 --> 00:12:26 So, when you add a metal to a protein you can do cool stuff. 189 00:12:26 --> 00:12:27 What can you do? 190 00:12:27 --> 00:12:29 Well, you can split nitrogen. 191 00:12:29 --> 00:12:32 You learned that the triple bond of nitrogen is pretty 192 00:12:32 --> 00:12:39 hard to break, but metals in proteins can do it. 193 00:12:39 --> 00:12:42 You've heard of hydrogen fuel cells and things like that. 194 00:12:42 --> 00:12:46 There's a protein called hydrogenase that uses metals to 195 00:12:46 --> 00:12:48 do chemistry with hydrogen. 196 00:12:48 --> 00:12:50 You could you radical based chemistry. 197 00:12:50 --> 00:12:52 You can do a lot of really great things when you have a 198 00:12:52 --> 00:12:57 protein that has a metal in it. 199 00:12:57 --> 00:13:00 So, let me introduce you to some of the concepts and 200 00:13:00 --> 00:13:04 terminology involved in this, so we're going to have a metal 201 00:13:04 --> 00:13:07 and the metal's going to be bound to stuff. 202 00:13:07 --> 00:13:10 So, one of the great features of transition metals is their 203 00:13:10 --> 00:13:15 ability to form complexes with small molecules or ions. 204 00:13:15 --> 00:13:19 They also, this applies to a protein system in the case that 205 00:13:19 --> 00:13:23 instead of small molecules, you have amino acids of proteins it 206 00:13:23 --> 00:13:27 can also form complexes with. 207 00:13:27 --> 00:13:32 So, the way that they do this is metals have often, they can 208 00:13:32 --> 00:13:35 attract electron density, usually a lone pair of 209 00:13:35 --> 00:13:38 electrons from another atom, and so they can form 210 00:13:38 --> 00:13:44 what are called these coordination complexes. 211 00:13:44 --> 00:13:47 So, now we're going to review for a minute, donor atoms, 212 00:13:47 --> 00:13:52 they're called ligands, and we can think about something that 213 00:13:52 --> 00:13:55 we learned when we talked about acids and bases, our 214 00:13:55 --> 00:13:57 more broad definition. 215 00:13:57 --> 00:14:01 So, donor atoms are ligands, and ligands are what? 216 00:14:01 --> 00:14:04 Lewis acids or Lewis bases, and what do they do? 217 00:14:04 --> 00:14:43 OK, let's just take 10 more seconds. 218 00:14:43 --> 00:14:48 So most of you thought donor atoms -- the answers that had 219 00:14:48 --> 00:14:52 donate electrons did better, so that was good reading of the 220 00:14:52 --> 00:14:58 question, but they are Lewis bases. 221 00:14:58 --> 00:15:02 So Lewis bases donate electron pairs. 222 00:15:02 --> 00:15:06 So, here's some examples that you will see of ligands 223 00:15:06 --> 00:15:08 that we'll be talking about in this unit. 224 00:15:08 --> 00:15:12 You will become very familiar with some of these as 225 00:15:12 --> 00:15:14 you work problems. 226 00:15:14 --> 00:15:21 So they're typically donating one lone pair of electrons. 227 00:15:21 --> 00:15:25 So, acceptor atoms are the transition metals themselves, 228 00:15:25 --> 00:15:29 and so the transition metals are acting as Lewis acids, and 229 00:15:29 --> 00:15:34 so then they would be accepting those lone pairs of electrons. 230 00:15:34 --> 00:15:37 So, you can think about coordination complexes as Lewis 231 00:15:37 --> 00:15:41 acids and Lewis bases, or acceptor atoms and donor 232 00:15:41 --> 00:15:46 ligands or donor atoms. 233 00:15:46 --> 00:15:49 So here are some examples of transition metals that we're 234 00:15:49 --> 00:15:53 going to see, so it's that sort of d-block of the periodic 235 00:15:53 --> 00:15:59 table that we'll become very familiar with in this unit. 236 00:15:59 --> 00:16:03 So, then when you take your acceptor atom and your donor 237 00:16:03 --> 00:16:06 atom and you put them together, you get what is known as 238 00:16:06 --> 00:16:08 coordination complexes. 239 00:16:08 --> 00:16:11 So, coordination complex is just the metal or the Lewis 240 00:16:11 --> 00:16:13 acid surrounded by the ligands, or the Lewis 241 00:16:13 --> 00:16:17 bases or the donor atoms. 242 00:16:17 --> 00:16:20 And here is an example of a coordination complex. 243 00:16:20 --> 00:16:23 We have metal, we have cobalt in the middle, and it's 244 00:16:23 --> 00:16:27 surrounded by a series of ligands, and these 245 00:16:27 --> 00:16:30 are n h 3 ligands. 246 00:16:30 --> 00:16:34 And so then our cobalt in the center, our metal, is the 247 00:16:34 --> 00:16:38 Lewis acid, and it's going to be the acceptor atom. 248 00:16:38 --> 00:16:42 And the n h 3 groups are our Lewis bases, they're donor 249 00:16:42 --> 00:16:46 atoms, see it's written with those two electrons there, that 250 00:16:46 --> 00:16:50 they're sharing their electrons with the cobalt forming 251 00:16:50 --> 00:16:52 this coordination complex. 252 00:16:52 --> 00:16:56 And in this scheme, we have the bonds are just these straight 253 00:16:56 --> 00:16:59 lines are in the plane, the thick bonds coming out are 254 00:16:59 --> 00:17:02 coming out toward you, and the dashed lines going back 255 00:17:02 --> 00:17:06 are going back into the screen here. 256 00:17:06 --> 00:17:11 So, let's talk about a couple of definitions here. 257 00:17:11 --> 00:17:14 We have something called coordination number or CN 258 00:17:14 --> 00:17:17 number, and this is simply the number of ligands 259 00:17:17 --> 00:17:19 bonded to the metal. 260 00:17:19 --> 00:17:22 So the number is six, there is six ligands. 261 00:17:22 --> 00:17:25 Typically, the numbers will range for these coordination 262 00:17:25 --> 00:17:33 complexes to two to 12, with six being the most common. 263 00:17:33 --> 00:17:36 So, here is some notation. 264 00:17:36 --> 00:17:38 If you see this picture, you should be able to write 265 00:17:38 --> 00:17:40 a notation for it. 266 00:17:40 --> 00:17:45 And within a bracket, you would write cobalt, and then you have 267 00:17:45 --> 00:17:48 your n h 3, six of them, so you put that in a bracket and 268 00:17:48 --> 00:17:50 indicate that there's six n h 3 groups. 269 00:17:50 --> 00:17:54 Then you have this overall bracket here with 270 00:17:54 --> 00:17:55 a charge up above. 271 00:17:55 --> 00:17:59 And so over here, we have this little bracket plus 3, that 272 00:17:59 --> 00:18:01 means that this whole coordination complex has 273 00:18:01 --> 00:18:03 a charge of plus 3. 274 00:18:03 --> 00:18:06 Because it has a positive charge, sometimes coordination 275 00:18:06 --> 00:18:09 complexes are associated with counter ions. 276 00:18:09 --> 00:18:13 So, you might see three chloride minus 1 ions around 277 00:18:13 --> 00:18:15 to counter that charge. 278 00:18:15 --> 00:18:18 And if you did, you would see the three chlorides on the 279 00:18:18 --> 00:18:19 outside of the bracket. 280 00:18:19 --> 00:18:23 So things inside of the bracket are actually coordinated to the 281 00:18:23 --> 00:18:27 metal, things outside the bracket are counter ions. 282 00:18:27 --> 00:18:30 And so that would be how you would translate that 283 00:18:30 --> 00:18:35 particular notation. 284 00:18:35 --> 00:18:38 All right, so, we're back to geometry again. 285 00:18:38 --> 00:18:40 As I said, everything you learn in this course, 286 00:18:40 --> 00:18:42 we're going to use again. 287 00:18:42 --> 00:18:46 So, if you're forgetting some material from units 1 and 288 00:18:46 --> 00:18:50 2, this would be a good time to review those. 289 00:18:50 --> 00:18:53 So, if we have this coordination number of six 290 00:18:53 --> 00:19:14 things around, what kind of geometry are we going to have? 291 00:19:14 --> 00:19:28 All right, 10 seconds. 292 00:19:28 --> 00:19:32 Yup, so we have octahedral geometry. 293 00:19:32 --> 00:19:37 And here is an example of our octahedral geometry. 294 00:19:37 --> 00:19:39 So, let's just quickly run through the rest of these. 295 00:19:39 --> 00:19:43 You can yell out the answers, either looking at your handout 296 00:19:43 --> 00:19:45 or not looking at your handout. 297 00:19:45 --> 00:19:51 The next one over here, what is it? 298 00:19:51 --> 00:19:51 Right, trigonal bipyramidal. 299 00:19:51 --> 00:19:56 For a c n number of five, we have another option shown over 300 00:19:56 --> 00:20:00 here, what's that one called? 301 00:20:00 --> 00:20:01 Square pyramidal. 302 00:20:01 --> 00:20:03 For c n numbers of four, there's two things that 303 00:20:03 --> 00:20:07 you'll commonly see, what's the first one called? 304 00:20:07 --> 00:20:08 Square planar. 305 00:20:08 --> 00:20:10 The second one? 306 00:20:10 --> 00:20:10 Tetrahedral. 307 00:20:10 --> 00:20:15 For c n number of three, what's that geometry called? 308 00:20:15 --> 00:20:16 Trigonal planar. 309 00:20:16 --> 00:20:20 And c n of two, only one option. 310 00:20:20 --> 00:20:20 Linear. 311 00:20:20 --> 00:20:24 All right, so let's just review the angles as well, those are 312 00:20:24 --> 00:20:28 not in your handouts, but you can yell those out as well. 313 00:20:28 --> 00:20:33 So what angle do we have in an octahedral system? 314 00:20:33 --> 00:20:34 90. 315 00:20:34 --> 00:20:37 There are two angles involved if we have trigonal 316 00:20:37 --> 00:20:38 bipyramidal. 317 00:20:38 --> 00:20:42 What's the angle from the axial to the equatorial? 318 00:20:42 --> 00:20:43 STUDENT: 90. 319 00:20:43 --> 00:20:46 PROFESSOR: And what's the angle from one equatorial atom to 320 00:20:46 --> 00:20:47 another equatorial atom? 321 00:20:47 --> 00:20:53 So, we have 90 and 120. 322 00:20:53 --> 00:20:57 What about in our square pyramidal system, what 323 00:20:57 --> 00:21:00 are the angles here? 324 00:21:00 --> 00:21:03 90. 325 00:21:03 --> 00:21:10 What about square planar? 326 00:21:10 --> 00:21:10 90. 327 00:21:10 --> 00:21:16 Tetrahedral? 328 00:21:16 --> 00:21:21 Let's try that again with more enthusiasm. 329 00:21:21 --> 00:21:22 Awesome, 109 . 330 00:21:22 --> 00:21:24 5. 331 00:21:24 --> 00:21:25 Trigonal planar? 332 00:21:25 --> 00:21:29 120. 333 00:21:29 --> 00:21:31 And finally, linear. 334 00:21:31 --> 00:21:37 180. 335 00:21:37 --> 00:21:40 So, we're going to use this information again in this unit, 336 00:21:40 --> 00:21:44 and of course, it'll be on the final when we're talking about 337 00:21:44 --> 00:21:46 Lewis structures and hybridization and 338 00:21:46 --> 00:21:47 other things as well. 339 00:21:47 --> 00:21:52 So this comes back in several times, vsper theory, you 340 00:21:52 --> 00:21:55 have this several times. 341 00:21:55 --> 00:21:58 OK. 342 00:21:58 --> 00:22:02 So, another term that you hear a lot when people are talking 343 00:22:02 --> 00:22:05 about coordination complexes is what's called the 344 00:22:05 --> 00:22:07 chelate effect. 345 00:22:07 --> 00:22:11 So, ligands that bind to a metal at one point are called 346 00:22:11 --> 00:22:17 unidentate or monodentate, and that's from dent, which 347 00:22:17 --> 00:22:21 is tooth, so one tooth. 348 00:22:21 --> 00:22:26 Now, if a ligand attaches with two or more points 349 00:22:26 --> 00:22:30 of attachment, it can be called a chelating ligand. 350 00:22:30 --> 00:22:34 And this comes from the Greek, chele is claw. 351 00:22:34 --> 00:22:38 So, if it's attaching with more than one point of attachment, 352 00:22:38 --> 00:22:41 if the ligand is grabbing on, it's like a claw and 353 00:22:41 --> 00:22:45 that's called a chelate. 354 00:22:45 --> 00:22:49 So, if you have two points of attachment, that's 355 00:22:49 --> 00:22:51 called bidentate. 356 00:22:51 --> 00:22:55 And even if you've never had a unit on transition metals 357 00:22:55 --> 00:22:58 before, I bet that you can answer this without 358 00:22:58 --> 00:23:00 me even telling you. 359 00:23:00 --> 00:23:05 What do you think tridentate might be? 360 00:23:05 --> 00:23:06 Three. 361 00:23:06 --> 00:23:08 Tetradentate? 362 00:23:08 --> 00:23:08 Four. 363 00:23:08 --> 00:23:10 Hexadentate? 364 00:23:10 --> 00:23:11 Six. 365 00:23:11 --> 00:23:14 So sometimes this would be a little question on the final. 366 00:23:14 --> 00:23:17 Please don't get this wrong, this is my gift to you, 367 00:23:17 --> 00:23:19 right, you knew it even before I taught it. 368 00:23:19 --> 00:23:22 So, this should be something that you can definitely get a 369 00:23:22 --> 00:23:24 couple extra points on on the final. 370 00:23:24 --> 00:23:29 All right, so, chelates bind with more than one point of 371 00:23:29 --> 00:23:35 attachment, and metal chelates are unusually stable. 372 00:23:35 --> 00:23:40 And this property is due to favorable and tropic factor, so 373 00:23:40 --> 00:23:43 we're back to entropy, we're back to thermodynamics. 374 00:23:43 --> 00:23:46 And this has to do with the fact that when a chelate binds 375 00:23:46 --> 00:23:49 a metal, it releases a lot of water, and that makes the 376 00:23:49 --> 00:23:53 chelate pretty stable. 377 00:23:53 --> 00:23:56 So, let me give you some examples of chelates, and then 378 00:23:56 --> 00:23:57 we're going to come back and think about the 379 00:23:57 --> 00:23:59 chelate effect again. 380 00:23:59 --> 00:24:06 Of course, you knew it, vitamin B12 has a chelating ligand 381 00:24:06 --> 00:24:11 associated with it. 382 00:24:11 --> 00:24:16 So, cobalt is in the middle of vitamin B12, and it has 383 00:24:16 --> 00:24:19 a ring system around it. 384 00:24:19 --> 00:24:22 And the ring system has these nitrogens, the nitrogens are 385 00:24:22 --> 00:24:26 the donor ligands to the cobalt, and so this ring system 386 00:24:26 --> 00:24:31 is attaching at four points, so it's a tetradentate ligand. 387 00:24:31 --> 00:24:34 There's also two other ligands attached to vitamin B12, 388 00:24:34 --> 00:24:37 there's an upper ligand shown here, which is 5 prime 389 00:24:37 --> 00:24:42 deoxyadenosine, and a bottom ligand, which is a 390 00:24:42 --> 00:24:42 dimethylbenzamitisol ligand. 391 00:24:42 --> 00:24:49 So, let's take a look, this is the cartoon, but let's look at 392 00:24:49 --> 00:24:51 another model for this here. 393 00:24:51 --> 00:24:56 So, we have a ring system, we have this upper ligand, and 394 00:24:56 --> 00:24:58 then a lower ligand down here. 395 00:24:58 --> 00:25:03 And so, the middle ring system is a tetradentate chelate. 396 00:25:03 --> 00:25:07 Overall, at the cobalt metal, what is the 397 00:25:07 --> 00:25:11 geometry of this system? 398 00:25:11 --> 00:25:12 It's octahedral, right. 399 00:25:12 --> 00:25:15 So we have this sort of square, the middle part is square 400 00:25:15 --> 00:25:18 planar, but the two upper and lower ligands make the whole 401 00:25:18 --> 00:25:21 thing an octahedral system. 402 00:25:21 --> 00:25:24 So this is an example of a naturally occurring 403 00:25:24 --> 00:25:28 chelated complex. 404 00:25:28 --> 00:25:30 So, this structure is actually fairly 405 00:25:30 --> 00:25:31 complicated for a vitamin. 406 00:25:31 --> 00:25:35 It's one of the most complex vitamins that's known, and 407 00:25:35 --> 00:25:38 I thought I'd just mention just a moment of history. 408 00:25:38 --> 00:25:42 So, this structure was determined by Dorothy Hodgkin 409 00:25:42 --> 00:25:45 who was a crystalographer in England. 410 00:25:45 --> 00:25:49 And she started working on this in the late 1940's, and people 411 00:25:49 --> 00:25:53 told her she was crazy, that something this large could 412 00:25:53 --> 00:25:56 never be solved by these x-ray defraction techniques. 413 00:25:56 --> 00:25:59 And, of course, now people are solving today's structures of 414 00:25:59 --> 00:26:00 things like the ribosomes. 415 00:26:00 --> 00:26:03 So, we've come a long way with crystallography. 416 00:26:03 --> 00:26:06 But she was one of the first true believers that x-ray 417 00:26:06 --> 00:26:08 crystallography was a powerful technique. 418 00:26:08 --> 00:26:12 And so, she went ahead, despite what everyone said, and 419 00:26:12 --> 00:26:14 determined this structure. 420 00:26:14 --> 00:26:16 And for this work and for some other things, she was 421 00:26:16 --> 00:26:17 awarded a Nobel Prize. 422 00:26:17 --> 00:26:20 So, this was a really significant contribution in the 423 00:26:20 --> 00:26:24 early 1950's and late 1940's. 424 00:26:24 --> 00:26:28 She had graduate students that she inspired. 425 00:26:28 --> 00:26:31 Some of them went on to become famous crystalographers. 426 00:26:31 --> 00:26:34 Other ones were not so successful -- crystallography's 427 00:26:34 --> 00:26:37 hard and it's not for everyone. 428 00:26:37 --> 00:26:41 She was actually known also, Dorothy was, for her work in 429 00:26:41 --> 00:26:44 the third world and her liberal politics, but one of her 430 00:26:44 --> 00:26:47 graduate students did not agree with her politics, but 431 00:26:47 --> 00:26:49 they were still friends. 432 00:26:49 --> 00:26:54 So this is just a message that as you go through your career, 433 00:26:54 --> 00:26:56 Margaret Thatcher who is a graduate student of Dorothy 434 00:26:56 --> 00:27:00 Hodgkins, couldn't quite cut it as a crystalographer, but for 435 00:27:00 --> 00:27:03 some people, you haven't found your true thing, and she was 436 00:27:03 --> 00:27:06 able to find another job, so I'm told. 437 00:27:06 --> 00:27:10 So, just remember that if you're not good at one thing, 438 00:27:10 --> 00:27:11 there's something else out there that you 439 00:27:11 --> 00:27:17 might be good at. 440 00:27:17 --> 00:27:22 So, let me give you a second example of a chelate. 441 00:27:22 --> 00:27:26 This molecule is known as EDTA. 442 00:27:26 --> 00:27:31 So this ligand has six points that it can attach to a metal. 443 00:27:31 --> 00:27:35 So, it is six atoms the can serve as these donor ligands. 444 00:27:35 --> 00:27:37 So, we have one up here, have the little electrons and the 445 00:27:37 --> 00:27:41 oxygen, another oxygen down here, nitrogen, nitrogen, 446 00:27:41 --> 00:27:44 another oxygen, another oxygen. 447 00:27:44 --> 00:27:49 So all of those six points can coordinate to a metal. 448 00:27:49 --> 00:27:54 So here again is the free EDTA, and here's a structure of 449 00:27:54 --> 00:27:59 EDTA bound to a metal, the metal is abbreviated m. 450 00:27:59 --> 00:28:24 So, why don't you tell me what the geometry is of that metal? 451 00:28:24 --> 00:28:39 All right, let's take only 10 more seconds. 452 00:28:39 --> 00:28:41 Hoping for 90, we're getting close, maybe 453 00:28:41 --> 00:28:42 by the end of today. 454 00:28:42 --> 00:28:46 All right, yeah, so it's octahedral geometry. 455 00:28:46 --> 00:28:50 So we have upper ligands and a lower ligand, two ligands 456 00:28:50 --> 00:28:55 coming out, two ligands going back, and it's also a 457 00:28:55 --> 00:28:57 hexadentate complex. 458 00:28:57 --> 00:28:59 So we see we're coordinated with the oxygen in red, 459 00:28:59 --> 00:29:02 nitrogen in blue, around to the other nitrogen in blue, another 460 00:29:02 --> 00:29:05 nitrogen in purple, another nitrogen up here in 461 00:29:05 --> 00:29:09 green and in blue. 462 00:29:09 --> 00:29:15 So, EDTA, when EDTA binds to a metal, it forms a very 463 00:29:15 --> 00:29:17 stable metal complex. 464 00:29:17 --> 00:29:19 And the reason for this is that chelate effect, 465 00:29:19 --> 00:29:21 and it's entropy. 466 00:29:21 --> 00:29:25 So if we look, metals are often coordinated by waters if 467 00:29:25 --> 00:29:26 they're just is solution. 468 00:29:26 --> 00:29:31 But if you bind one molecule of EDTA to the metal, it'll take 469 00:29:31 --> 00:29:34 all of those six sites, displacing all of 470 00:29:34 --> 00:29:35 these six waters. 471 00:29:35 --> 00:29:39 So here, on this side, you have one thing free in solution, and 472 00:29:39 --> 00:29:42 over here you have six things that are free. 473 00:29:42 --> 00:29:45 So that's entrotropically favorable, you have more 474 00:29:45 --> 00:29:48 entropy when you have lots of more free things 475 00:29:48 --> 00:29:49 floating around. 476 00:29:49 --> 00:29:51 So this has greater entropy. 477 00:29:51 --> 00:29:58 So, the chelate effect, then, has to do with entropic effect, 478 00:29:58 --> 00:30:00 that when you're binding a metal with multiple points of 479 00:30:00 --> 00:30:02 attachments, it's releasing water. 480 00:30:02 --> 00:30:04 So these are very stable. 481 00:30:04 --> 00:30:08 And so, because of this stability, they have a 482 00:30:08 --> 00:30:11 lot of important uses. 483 00:30:11 --> 00:30:14 What is one use you can think of that you might have 484 00:30:14 --> 00:30:15 for such a thing? 485 00:30:15 --> 00:30:20 When might you want to chelate a metal out -- get metal out 486 00:30:20 --> 00:30:21 of something pretty quickly. 487 00:30:21 --> 00:30:23 Yeah. 488 00:30:23 --> 00:30:28 Yeah, you can purify out a metal out of water with this. 489 00:30:28 --> 00:30:34 What about rushing to the emergency room with something? 490 00:30:34 --> 00:30:37 Yeah, lead poisoning, yup. 491 00:30:37 --> 00:30:40 So, sometimes you might want to just purify your water, you 492 00:30:40 --> 00:30:43 might be happy with that, other times you might really want 493 00:30:43 --> 00:30:45 to have that metal out. 494 00:30:45 --> 00:30:50 So, every emergency room in the United States, and probably 495 00:30:50 --> 00:30:54 mostly around the world, will have EDTA on hand in case 496 00:30:54 --> 00:30:57 someone comes in with lead poisoning. 497 00:30:57 --> 00:31:01 Do you know who's at the most risk for lead poisoning, 498 00:31:01 --> 00:31:03 at least in this country? 499 00:31:03 --> 00:31:04 Kids. 500 00:31:04 --> 00:31:07 And what do they do they gives them lead poisoning? 501 00:31:07 --> 00:31:08 Lead paint, yeah. 502 00:31:08 --> 00:31:11 So, I don't know, most of you are probably living on campus, 503 00:31:11 --> 00:31:15 but if any of you move off campus, and some people who are 504 00:31:15 --> 00:31:18 living maybe across the river in fraternity houses, those 505 00:31:18 --> 00:31:21 buildings are old and they have had lead paint in at 506 00:31:21 --> 00:31:22 some point or another. 507 00:31:22 --> 00:31:25 So this is a big problem, actually, in the Boston area. 508 00:31:25 --> 00:31:28 So, if you have any toddlers visiting you, you might want to 509 00:31:28 --> 00:31:32 make sure they're not eating paint chips off any window 510 00:31:32 --> 00:31:33 sill or anything like that. 511 00:31:33 --> 00:31:38 Or if you do, have some EDTA on hand. 512 00:31:38 --> 00:31:41 All right, one other thing, some of you, once you start 513 00:31:41 --> 00:31:46 studying chemistry, it's always fun/scary to start reading the 514 00:31:46 --> 00:31:49 ingredients on food packages. 515 00:31:49 --> 00:31:53 But you will discover that some food that you eat will say 516 00:31:53 --> 00:31:57 as an ingredient EDTA added for freshness. 517 00:31:57 --> 00:32:02 So, bacteria and fungi and things like that need metals 518 00:32:02 --> 00:32:05 for growth, metals are very important for life, and so 519 00:32:05 --> 00:32:08 you add a little EDTA and it prevents things from 520 00:32:08 --> 00:32:10 growing on your food. 521 00:32:10 --> 00:32:14 So that's added for freshness. 522 00:32:14 --> 00:32:16 So you'll see it in food. 523 00:32:16 --> 00:32:21 Another use that occasionally I find MIT students are not as 524 00:32:21 --> 00:32:27 familiar with is in cleaning bathtubs, so you want to 525 00:32:27 --> 00:32:31 chelate out the calcium in tub scum, and that's a 526 00:32:31 --> 00:32:34 good use for EDTA. 527 00:32:34 --> 00:32:37 So, I always like to mention how freshman chemistry 528 00:32:37 --> 00:32:40 information can make you a lot of money. 529 00:32:40 --> 00:32:42 So, I thought I'd tell you a little story about a 530 00:32:42 --> 00:32:45 man named Robert Black. 531 00:32:45 --> 00:32:48 So one day, I think it might have been a little before 532 00:32:48 --> 00:32:51 Thanksgiving, Mrs. Robert Black, I don't know her first 533 00:32:51 --> 00:32:55 name, said to her husband, "We're having company, how 534 00:32:55 --> 00:33:01 about you go clean the bathtub?" Apparently, Robert 535 00:33:01 --> 00:33:04 Black's wife had never mentioned this to him before, 536 00:33:04 --> 00:33:07 and he had, in fact, never cleaned a bathtub. 537 00:33:07 --> 00:33:11 Also, I think that Robert Black's wife was tired of 538 00:33:11 --> 00:33:14 cleaning the bathtub, and perhaps, had not done it 539 00:33:14 --> 00:33:17 for, say, a very long time. 540 00:33:17 --> 00:33:21 So, Robert Black went in there and tried to scrub off the 541 00:33:21 --> 00:33:23 scum, and it was actually really challenging and he was 542 00:33:23 --> 00:33:26 very frustrating, and he said, "I never want to 543 00:33:26 --> 00:33:28 do that again." 544 00:33:28 --> 00:33:33 So, he went and developed a product, a shower cleaner, that 545 00:33:33 --> 00:33:36 had all the ingredients of the shower cleaners he was using, 546 00:33:36 --> 00:33:39 except that he advertised it slightly differently, and he 547 00:33:39 --> 00:33:45 said "Every time you shower, just spray a little bit on and 548 00:33:45 --> 00:33:47 you'll never have to really scrub again." because this will 549 00:33:47 --> 00:33:50 take care of it and avoid scrubbing in the future, so a 550 00:33:50 --> 00:33:53 little bit of spraying after each shower avoids 551 00:33:53 --> 00:33:55 these problems. 552 00:33:55 --> 00:33:58 And the ingredients he had in were all typical ingredients, 553 00:33:58 --> 00:34:00 including chelating agents. 554 00:34:00 --> 00:34:05 You need a surfactant to break up the water beads, and alcohol 555 00:34:05 --> 00:34:08 to get rid of the oily stuff, and the chelating agent for 556 00:34:08 --> 00:34:09 the calcium in the tub scum. 557 00:34:09 --> 00:34:14 And the one he actually used is EDTA. 558 00:34:14 --> 00:34:18 So, as a result of a wife saying to her husband, it's 559 00:34:18 --> 00:34:22 your turn to clean the tub, they now make $70 million 560 00:34:22 --> 00:34:24 dollars annually. 561 00:34:24 --> 00:34:29 So, I think this is a lesson that we can learn in many ways 562 00:34:29 --> 00:34:32 that cleaning the tub is something that everyone should 563 00:34:32 --> 00:34:36 do at some point in their life, and that the simple things you 564 00:34:36 --> 00:34:40 learn in freshman chemistry can, if applied correctly, 565 00:34:40 --> 00:34:42 make you a lot of money. 566 00:34:42 --> 00:34:44 And I just want to encourage you, again, that anything that 567 00:34:44 --> 00:34:47 I teach you that you use to make a lot of money, I'll 568 00:34:47 --> 00:34:49 remind you that I am perfectly willing to have a 569 00:34:49 --> 00:34:51 cut of any of that. 570 00:34:51 --> 00:34:55 So, just something to keep in mind. 571 00:34:55 --> 00:35:00 So, one more thing that you might have heard for EDTA. 572 00:35:00 --> 00:35:05 Have any of you heard, perhaps, maybe watching television or a 573 00:35:05 --> 00:35:14 movie, about a use for EDTA? 574 00:35:14 --> 00:35:20 Have any of you, perhaps, seen a movie called Blade? 575 00:35:20 --> 00:35:23 How many of you have seen this? 576 00:35:23 --> 00:35:25 Not very many people. 577 00:35:25 --> 00:35:28 Hmm, I think we're going to have a separate course in 578 00:35:28 --> 00:35:34 vampire movies and TV. 579 00:35:34 --> 00:35:39 Anyway, Blade fights vampires, and they have a special gun, 580 00:35:39 --> 00:35:42 and the special gun has cartridges -- cartridges 581 00:35:42 --> 00:35:44 are shown here. 582 00:35:44 --> 00:35:47 And the cartridges have in them -- anyone want to guess? 583 00:35:47 --> 00:35:49 EDTA, yes. 584 00:35:49 --> 00:35:54 And the idea behind it, if you shoot at a vampire, the vampire 585 00:35:54 --> 00:35:58 turns instantaneously to dust, and the idea behind it is that 586 00:35:58 --> 00:36:02 vampires drink blood, blood has what in it? 587 00:36:02 --> 00:36:04 Iron. 588 00:36:04 --> 00:36:04 What chelates iron? 589 00:36:04 --> 00:36:06 EDTA. 590 00:36:06 --> 00:36:10 And, therefore, if you chelate the iron out of blood, and a 591 00:36:10 --> 00:36:15 vampire's mostly blood, it just instantaneously turns to dust. 592 00:36:15 --> 00:36:21 So, actually, as chemistry goes, it's kind of cool, yeah. 593 00:36:21 --> 00:36:25 So, that's the final use that I am aware of for EDTA. 594 00:36:25 --> 00:36:30 Some of you may encounter some more. 595 00:36:30 --> 00:36:36 All right, so coordination complexes. 596 00:36:36 --> 00:36:39 Some of them can have isomers. 597 00:36:39 --> 00:36:42 They can have geometric isomers. 598 00:36:42 --> 00:36:46 And geometric isomers can have vastly different properties. 599 00:36:46 --> 00:36:50 And if you're interested in biochemistry, this is something 600 00:36:50 --> 00:36:54 that you'll be interested in, because this can be 601 00:36:54 --> 00:36:57 very important in biological systems. 602 00:36:57 --> 00:37:01 So, let me tell you about a coordination complex that has 603 00:37:01 --> 00:37:06 platinum at the center, it has two ammonia ligands and two 604 00:37:06 --> 00:37:12 chloride ligands, and it has two ways that you can do it. 605 00:37:12 --> 00:37:16 So, you can either put the ammonia ligands on different 606 00:37:16 --> 00:37:19 sides or you can put them on the same side. 607 00:37:19 --> 00:37:23 So, here we have two nitrogen ligands over here, and 608 00:37:23 --> 00:37:25 I have these here. 609 00:37:25 --> 00:37:30 So, on one side, you have the two nitrogen ligands, on the 610 00:37:30 --> 00:37:36 other side two chlorides, or we can have a transarrangement 611 00:37:36 --> 00:37:38 where they're across from each other. 612 00:37:38 --> 00:37:41 So you see, there's 2 different ways to do it, on the same 613 00:37:41 --> 00:37:43 side or sort of across. 614 00:37:43 --> 00:37:45 So, cis or trans. 615 00:37:45 --> 00:37:52 Cisplatin is a potent anti-cancer drug, transplatin 616 00:37:52 --> 00:37:55 has no use that anyone's been able to detect. 617 00:37:55 --> 00:37:58 So it's the exact same composition, but a different 618 00:37:58 --> 00:38:01 arrangement of the atoms coordinated to the 619 00:38:01 --> 00:38:02 central metal. 620 00:38:02 --> 00:38:05 So, why should it make a difference, they have the same 621 00:38:05 --> 00:38:10 ingredients, why should one be a potent anti-cancer drug and 622 00:38:10 --> 00:38:12 the other one be useless? 623 00:38:12 --> 00:38:16 Well, it's because of how it interacts in the body. 624 00:38:16 --> 00:38:20 And so, one of the people who have spent a lot of their 625 00:38:20 --> 00:38:24 career studying cisplatin is Professor Steve Lippard, who's 626 00:38:24 --> 00:38:27 in the Chemistry Department here, and he has determined 627 00:38:27 --> 00:38:30 x-ray structures looking at this, and done a number 628 00:38:30 --> 00:38:31 of other studies. 629 00:38:31 --> 00:38:35 And so, here is a little cartoon of cisplatin bound to 630 00:38:35 --> 00:38:39 DNA, so the chlorides are displaced when it binds, and so 631 00:38:39 --> 00:38:42 they need to be on the same side, otherwise it's 632 00:38:42 --> 00:38:44 not going to work. 633 00:38:44 --> 00:38:50 And when cisplatin binds to DNA, then this will act 634 00:38:50 --> 00:38:54 to kill the cancer cells. 635 00:38:54 --> 00:38:58 So, the chlorides both need to be on the same side 636 00:38:58 --> 00:38:59 so a combined DNA. 637 00:38:59 --> 00:39:02 If they're on other sides, that's not going to interact 638 00:39:02 --> 00:39:06 with DNA, and so it doesn't have any known function. 639 00:39:06 --> 00:39:11 So, geometric isomers, same composition, but in different 640 00:39:11 --> 00:39:18 arrangements can have vastly different properties. 641 00:39:18 --> 00:39:21 So you can have what are called optical isomers or enantiomers, 642 00:39:21 --> 00:39:25 and so these can our mirror images of each other, but 643 00:39:25 --> 00:39:27 they're not superimposable. 644 00:39:27 --> 00:39:30 And so, when you have a mirror image like this, it's called a 645 00:39:30 --> 00:39:34 chiral molecule, and this is a term that you'll hear 646 00:39:34 --> 00:39:37 a lot when you take organic chemistry. 647 00:39:37 --> 00:39:41 So, I have two mirror images up here, so these are mirror 648 00:39:41 --> 00:39:45 images, so the mirror plane is between these molecules. 649 00:39:45 --> 00:39:48 But these molecules may look the same in the mirror, but 650 00:39:48 --> 00:39:49 they're non-superimposable. 651 00:39:49 --> 00:39:54 So, they are, in fact, different molecules, and they 652 00:39:54 --> 00:39:59 can have different properties in a chiral environment. 653 00:39:59 --> 00:40:02 What do I mean by a chiral environment? 654 00:40:02 --> 00:40:04 Well, the human body, for example, is a 655 00:40:04 --> 00:40:08 chiral environment. 656 00:40:08 --> 00:40:11 So that's why a lot of drugs, people are wanting to make just 657 00:40:11 --> 00:40:14 one enantimer of the drug and not the other, one enantiomer 658 00:40:14 --> 00:40:19 can have good properties, the other one may not. 659 00:40:19 --> 00:40:24 All right, so let's do some d-electron counting. 660 00:40:24 --> 00:40:26 This is the final thing we need to talk about in 661 00:40:26 --> 00:40:31 coordination complexes. 662 00:40:31 --> 00:40:35 So we're going to refer to a thing called the d-electron 663 00:40:35 --> 00:40:39 count of the metal, which just has to do with a group number 664 00:40:39 --> 00:40:43 from the periodic table minus the oxidation number of the 665 00:40:43 --> 00:40:46 metal, is going to tell us the d-electron count. 666 00:40:46 --> 00:40:50 So, if you haven't learned how to do oxidation numbers yet, 667 00:40:50 --> 00:40:53 you need to know that for exam 3, and you need to know 668 00:40:53 --> 00:40:55 that for this unit. 669 00:40:55 --> 00:40:58 So, let's look at a few examples of this, and 670 00:40:58 --> 00:41:02 we'll put up our friend, the periodic table. 671 00:41:02 --> 00:41:07 So let's look at the complex that we saw on the first page 672 00:41:07 --> 00:41:10 where we had -- in the beginning of today's lecture 673 00:41:10 --> 00:41:16 where we had cobalts with six n h 3 ligands in a coordination 674 00:41:16 --> 00:41:20 complex that had a charge of plus 3. 675 00:41:20 --> 00:41:24 So here, we need to figure out the oxidation number of the 676 00:41:24 --> 00:41:29 cobalt, and for this particular group, the overall 677 00:41:29 --> 00:41:30 charge of that is 0. 678 00:41:30 --> 00:41:35 We have three hydrogens at plus 1, and we also have 679 00:41:35 --> 00:41:38 a nitrogen at minus 1. 680 00:41:38 --> 00:41:41 And so, overall that charge is 0. 681 00:41:41 --> 00:41:46 So we have six things of 0, and what does that leave 682 00:41:46 --> 00:41:49 for our cobalt charge? 683 00:41:49 --> 00:41:51 Plus 3. 684 00:41:51 --> 00:41:55 Because overall, it now has to equal plus 3. 685 00:41:55 --> 00:42:00 So, then our d count for our electrons is going 686 00:42:00 --> 00:42:02 to be the group number. 687 00:42:02 --> 00:42:05 And for cobalt, what's the group number? 688 00:42:05 --> 00:42:07 9. 689 00:42:07 --> 00:42:14 So minus 3 is 6, so this cobalt in this complex is what's 690 00:42:14 --> 00:42:21 called a d 6 system. 691 00:42:21 --> 00:42:31 All right, let's look at a couple other examples here. 692 00:42:31 --> 00:42:35 Let's look at nickel with carbon monoxide 693 00:42:35 --> 00:42:40 ligands, four of them. 694 00:42:40 --> 00:42:47 What would nickel be in this case? 695 00:42:47 --> 00:42:48 Someone said zero. 696 00:42:48 --> 00:42:49 That's right. 697 00:42:49 --> 00:42:54 So this is zero, and nickel is zero, the overall 698 00:42:54 --> 00:42:56 charge is zero. 699 00:42:56 --> 00:43:03 So, our oxidation number here is 0. 700 00:43:03 --> 00:43:09 So, our d count here, what's the group number for nickel? 701 00:43:09 --> 00:43:10 10. 702 00:43:10 --> 00:43:14 10 minus 0 is 10. 703 00:43:14 --> 00:43:20 So we have a d 10 system. 704 00:43:20 --> 00:43:24 So, I'm going to write another example down and you're going 705 00:43:24 --> 00:43:28 to tell me the answer to this one as a clicker question. 706 00:43:28 --> 00:43:42 So we have cobalt, two waters -- three waters -- that's 707 00:43:42 --> 00:43:43 actually a mistake. 708 00:43:43 --> 00:43:45 It should be two. 709 00:43:45 --> 00:43:50 Two waters, because it's going to be six things -- this is not 710 00:43:50 --> 00:43:54 some kind of bizzaro seven complex. 711 00:43:54 --> 00:43:58 So here's the correct, cobalt, two waters, one ammonia, 712 00:43:58 --> 00:44:32 and three chlorides with an overall charge of minus 1. 713 00:44:32 --> 00:44:34 All right, let's just take 10 seconds, since we're 714 00:44:34 --> 00:44:49 running out of time. 715 00:44:49 --> 00:44:53 So that's right, we should have a charge of plus 2 here. 716 00:44:53 --> 00:45:00 This is zero, 0 minus 3, overall minus 1, so we 717 00:45:00 --> 00:45:01 have a plus 2 state. 718 00:45:01 --> 00:45:07 We have 9 minus 2, which is 7, and it's a d 7 system.