1
00:00:00,000 --> 00:00:00,016
The following content is
provided under a Creative

2
00:00:00,016 --> 00:00:00,022
Commons license.

3
00:00:00,022 --> 00:00:00,038
Your support will help MIT
OpenCourseWare continue to

4
00:00:00,038 --> 00:00:00,054
offer high quality educational
resources for free.

5
00:00:00,054 --> 00:00:00,072
To make a donation or view
additional materials from

6
00:00:00,072 --> 00:00:00,088
hundreds of MIT courses, visit
MIT OpenCourseWare at

7
00:00:00,088 --> 00:00:00,110
ocw.mit.edu.

8
00:00:00,110 --> 00:00:23,620
PROFESSOR: OK, everyone,
pay attention

9
00:00:23,620 --> 00:00:24,930
to the clicker question.

10
00:00:24,930 --> 00:00:27,860
If you haven't responded, now's
a good time to click in

11
00:00:27,860 --> 00:00:46,000
your response.

12
00:00:46,000 --> 00:01:04,330
All right, let's just take
10 more seconds.

13
00:01:04,330 --> 00:01:13,170
OK, we can do better
than this.

14
00:01:13,170 --> 00:01:17,650
So, tetrahedral complexes.

15
00:01:17,650 --> 00:01:21,710
Do you recall tetrahedral
complexes with angles of what

16
00:01:21,710 --> 00:01:24,770
between the ligands?

17
00:01:24,770 --> 00:01:25,750
109 .

18
00:01:25,750 --> 00:01:28,120
5.

19
00:01:28,120 --> 00:01:33,070
The ligands' negative point
charges aren't facing any of

20
00:01:33,070 --> 00:01:36,740
the d orbitals perfectly.

21
00:01:36,740 --> 00:01:40,030
They're a little bit closer to
the orbitals that are 45

22
00:01:40,030 --> 00:01:44,980
degrees off-axis, so those three
are the most repelled.

23
00:01:44,980 --> 00:01:48,210
But they're not really directly
hitting any of them.

24
00:01:48,210 --> 00:01:51,450
So that's in contrast with the
octahedral system or square

25
00:01:51,450 --> 00:01:54,270
planar where the ligands
negative point charges are

26
00:01:54,270 --> 00:01:56,950
headed directly toward some
of the d orbitals.

27
00:01:56,950 --> 00:02:00,750
So because the ligands in a
tetrahedral case are not

28
00:02:00,750 --> 00:02:04,870
headed directly toward any of
the d orbitals, there is not a

29
00:02:04,870 --> 00:02:09,870
huge amount of crystal fields
splitting, so that's small.

30
00:02:09,870 --> 00:02:13,960
And so, when the splitting is
small, then you tend to have

31
00:02:13,960 --> 00:02:18,810
high spin systems. So you put in
all of the electrons singly

32
00:02:18,810 --> 00:02:21,070
to the fullest extent
of the orbital as

33
00:02:21,070 --> 00:02:23,170
possible before you pair.

34
00:02:23,170 --> 00:02:26,980
And so, since you put them in
singly for the fullest extent

35
00:02:26,980 --> 00:02:30,690
possible before you pair them
up, that will lead to a high

36
00:02:30,690 --> 00:02:33,120
spin system, which
is the maximum

37
00:02:33,120 --> 00:02:34,810
number of unpaired electrons.

38
00:02:34,810 --> 00:02:41,490
So today is then the last
lecture on transition metals,

39
00:02:41,490 --> 00:02:43,890
and we've been talking about
crystal field theory, and

40
00:02:43,890 --> 00:02:48,480
today we're going to talk
about colors and

41
00:02:48,480 --> 00:02:50,980
crystal field theory.

42
00:02:50,980 --> 00:02:57,670
So, colors, there are a lot of
beautiful colors in nature,

43
00:02:57,670 --> 00:03:01,490
and some of the beautiful colors
you find in nature have

44
00:03:01,490 --> 00:03:08,140
to do with transition metals
or other liganded states.

45
00:03:08,140 --> 00:03:12,350
So, we're going to start with
an example of how colors can

46
00:03:12,350 --> 00:03:15,830
change, how a molecule's color
can depend on its oxidation

47
00:03:15,830 --> 00:03:19,140
state, how a molecule's
color can depend on

48
00:03:19,140 --> 00:03:20,970
its liganded state.

49
00:03:20,970 --> 00:03:27,440
So, Dr. Taylor is going to be
doing this for you -- should

50
00:03:27,440 --> 00:03:30,426
we do it the demo and then look
at the questions or do

51
00:03:30,426 --> 00:03:31,600
the questions first?

52
00:03:31,600 --> 00:03:32,790
Demo first?

53
00:03:32,790 --> 00:03:36,900
PROFESSOR: OK.

54
00:03:36,900 --> 00:03:39,650
PROFESSOR: So, here are some
of the reactions up on the

55
00:03:39,650 --> 00:03:43,270
Powerpoint that you're going to
be looking at, and as the

56
00:03:43,270 --> 00:03:46,330
reaction proceeds, there's
going to be changes in

57
00:03:46,330 --> 00:03:50,090
oxidation state, and also
changes in ligand in state,

58
00:03:50,090 --> 00:03:52,550
and that will lead to
changes in color.

59
00:03:52,550 --> 00:04:49,460
[DEMONSTRATION]

60
00:04:49,460 --> 00:04:58,530
PROFESSOR: So, how would you
describe that first color?

61
00:04:58,530 --> 00:04:59,420
Any predictions?

62
00:04:59,420 --> 00:05:01,100
Have any of you seen
this before, what's

63
00:05:01,100 --> 00:05:19,000
going to happen next?

64
00:05:19,000 --> 00:05:19,590
[DEMONSTRATION]

65
00:05:19,590 --> 00:05:36,350
PROFESSOR: So this is called an
oscillating clock reaction,

66
00:05:36,350 --> 00:05:39,310
so as it runs through,
it cycles between

67
00:05:39,310 --> 00:05:56,690
the different colors.

68
00:05:56,690 --> 00:06:01,360
So, that should happily keep
going, and we can consider

69
00:06:01,360 --> 00:06:02,460
what's happening.

70
00:06:02,460 --> 00:06:05,430
So here's the overall reaction
here and it can be divided

71
00:06:05,430 --> 00:06:07,640
into two components.

72
00:06:07,640 --> 00:06:12,310
So, why don't you tell me, what
is happening to iodide in

73
00:06:12,310 --> 00:07:08,420
that first reaction, and
there it is again.

74
00:07:08,420 --> 00:07:23,770
All right, so let's take
10 more seconds.

75
00:07:23,770 --> 00:07:25,680
Very good.

76
00:07:25,680 --> 00:07:29,890
So, if you looked up here, you
see that you have minus 2 for

77
00:07:29,890 --> 00:07:33,680
the oxygen, three of them, minus
6, and it needs to equal

78
00:07:33,680 --> 00:07:36,170
minus 1, so you have plus 5.

79
00:07:36,170 --> 00:07:40,610
And then over here, we again
have plus 1 minus 2, and so

80
00:07:40,610 --> 00:07:42,660
that has to be plus 1.

81
00:07:42,660 --> 00:07:47,800
So that was actually a quiz
question, but you score three

82
00:07:47,800 --> 00:07:51,430
points if you answered, even
if you got it wrong, but we

83
00:07:51,430 --> 00:07:53,840
could have had that four points,
most people got that

84
00:07:53,840 --> 00:07:54,640
right anyway.

85
00:07:54,640 --> 00:07:56,830
But if you answered, you
get an extra few

86
00:07:56,830 --> 00:07:58,770
points on that one.

87
00:07:58,770 --> 00:08:01,070
All right, so very good.

88
00:08:01,070 --> 00:08:03,140
That's what's happening
to iodide.

89
00:08:03,140 --> 00:08:07,230
Now you notice that in this
reaction h o i is being

90
00:08:07,230 --> 00:08:08,640
produced, and then
in the second

91
00:08:08,640 --> 00:08:12,690
step it's being consumed.

92
00:08:12,690 --> 00:08:16,100
This later reaction can be
divided, then, into two

93
00:08:16,100 --> 00:08:20,240
additional reactions.

94
00:08:20,240 --> 00:08:24,200
And one of the reactions, you
can tell me again what is

95
00:08:24,200 --> 00:08:26,870
happening, what is being
oxidized and what is being

96
00:08:26,870 --> 00:09:09,130
reduced in this part
of the reaction.

97
00:09:09,130 --> 00:09:22,740
OK, let's take 10 more seconds.

98
00:09:22,740 --> 00:09:23,970
Excellent.

99
00:09:23,970 --> 00:09:26,230
Even a little higher
than before.

100
00:09:26,230 --> 00:09:29,010
All right, so you figured out
that this was the plus 1, this

101
00:09:29,010 --> 00:09:31,670
is minus 1, and they're
both going to 0.

102
00:09:31,670 --> 00:09:35,230
So you have oxidation and
reduction going on all

103
00:09:35,230 --> 00:09:41,880
involving iodide in
that reaction.

104
00:09:41,880 --> 00:09:45,830
OK, so as the reaction was
proceeding, you could see that

105
00:09:45,830 --> 00:09:49,470
it started out with clear and
then it went to sort of amber

106
00:09:49,470 --> 00:09:53,470
color, and that was the i 2, the
clear was i minus, and the

107
00:09:53,470 --> 00:09:56,760
sort of darker blue color that
you saw is the complex with

108
00:09:56,760 --> 00:09:58,390
starch in the reaction.

109
00:09:58,390 --> 00:10:01,850
So that both of these guys have
colors independent, but

110
00:10:01,850 --> 00:10:04,240
then when they're liganded
to something else,

111
00:10:04,240 --> 00:10:05,570
the color is different.

112
00:10:05,570 --> 00:10:09,050
And that's very true with
coordination complexes that

113
00:10:09,050 --> 00:10:13,650
the metal by itself will be
strongly influenced by what

114
00:10:13,650 --> 00:10:14,730
the ligands are.

115
00:10:14,730 --> 00:10:17,490
And depending on what type of
ligands it has, it can have a

116
00:10:17,490 --> 00:10:21,880
really entirely different color
than it had before.

117
00:10:21,880 --> 00:10:24,770
So, today we're going to talk
about why that's true, and how

118
00:10:24,770 --> 00:10:27,630
you can predict colors based
on what type of ligand is

119
00:10:27,630 --> 00:10:30,880
bound to a transition metal.

120
00:10:30,880 --> 00:10:34,290
So, a lot of transition metals
have really beautiful colors,

121
00:10:34,290 --> 00:10:38,360
and my laboratory studies metals
bound to proteins, and

122
00:10:38,360 --> 00:10:41,130
often the proteins will have
really beautiful colors

123
00:10:41,130 --> 00:10:44,900
because of the metal cofactor
involved, and that's one of

124
00:10:44,900 --> 00:10:48,550
the things that I liked about
that particular area of study

125
00:10:48,550 --> 00:10:52,940
is just how beautiful these
proteins can be.

126
00:10:52,940 --> 00:10:55,800
So, the color given off depends
on the nature of the

127
00:10:55,800 --> 00:10:57,860
metal, and depends on the
nature of the ligand.

128
00:10:57,860 --> 00:11:01,300
And so we can use crystal field
theory, which again, is

129
00:11:01,300 --> 00:11:06,800
a very simplified theory, to try
to predict or explain the

130
00:11:06,800 --> 00:11:08,320
observed colors.

131
00:11:08,320 --> 00:11:13,420
And so again, this is not
always very precise, but

132
00:11:13,420 --> 00:11:16,050
given, if you're told
information out of color, you

133
00:11:16,050 --> 00:11:19,460
can rationalize why that would
be true, and you can also

134
00:11:19,460 --> 00:11:22,060
predict at least a range of
color that you would have

135
00:11:22,060 --> 00:11:23,960
under certain circumstances.

136
00:11:23,960 --> 00:11:28,100
So, let's take a look
at this more.

137
00:11:28,100 --> 00:11:30,220
So the ligands again,
have the ability to

138
00:11:30,220 --> 00:11:31,130
split those d orbitals.

139
00:11:31,130 --> 00:11:33,960
And when we're talking about for
metals, it's all about the

140
00:11:33,960 --> 00:11:35,100
d orbitals.

141
00:11:35,100 --> 00:11:38,770
And we talked already about
strong field ligands and weak

142
00:11:38,770 --> 00:11:41,410
field ligands, and we're going
to talk more about that today,

143
00:11:41,410 --> 00:11:43,530
but this time in
terms of color.

144
00:11:43,530 --> 00:11:47,190
So a strong field ligand, as
we discussed, creates a big

145
00:11:47,190 --> 00:11:51,070
splitting in the d orbital
energy, whereas weak field

146
00:11:51,070 --> 00:11:54,540
ligand, like the first question
you had today with

147
00:11:54,540 --> 00:11:58,730
tetrahedral complexes, there's
usually a weak field there, so

148
00:11:58,730 --> 00:12:01,040
we have a small energy
separation

149
00:12:01,040 --> 00:12:05,050
between the d orbitals.

150
00:12:05,050 --> 00:12:07,940
So here is something that you
actually have to memorize --

151
00:12:07,940 --> 00:12:10,890
there's not much memorization
in this course, but you do

152
00:12:10,890 --> 00:12:14,620
need to memorize these six
ligands in terms of their

153
00:12:14,620 --> 00:12:18,050
ability to split d orbitals.

154
00:12:18,050 --> 00:12:21,190
So, on the side, we have three
that are strong field ligands,

155
00:12:21,190 --> 00:12:27,630
cyanide, c o, and ammonia, and
so those are going to be

156
00:12:27,630 --> 00:12:30,610
strong field, so they're going
to have big splitting energy,

157
00:12:30,610 --> 00:12:32,960
and so they'll tend
to be low spin.

158
00:12:32,960 --> 00:12:36,070
Then we have three that are sort
of in between that are

159
00:12:36,070 --> 00:12:40,710
intermediate field -- water,
hydroxide and f minus.

160
00:12:40,710 --> 00:12:45,330
And so, in comparing, those are
intermediate, so you're

161
00:12:45,330 --> 00:12:48,640
going to be asked questions such
as how does that compare

162
00:12:48,640 --> 00:12:51,940
to a weak field, how does that
compare to a strong field.

163
00:12:51,940 --> 00:12:54,640
And then our weak field ligands
or a lot of our

164
00:12:54,640 --> 00:12:59,750
halides down here, i minus,
b r minus, c l minus.

165
00:12:59,750 --> 00:13:02,130
And so those are weak field
ligands, so you'll have a

166
00:13:02,130 --> 00:13:04,760
small splitting, so
they'll tend to be

167
00:13:04,760 --> 00:13:09,110
in high spin complexes.

168
00:13:09,110 --> 00:13:16,930
So let's take a look
at some examples.

169
00:13:16,930 --> 00:13:21,430
So we talked about iron before
in complexes, and now we can

170
00:13:21,430 --> 00:13:26,960
consider two cases where we have
iron plus 3, so the same

171
00:13:26,960 --> 00:13:30,090
metal in the same oxidation
state, but it

172
00:13:30,090 --> 00:13:30,950
has different ligands.

173
00:13:30,950 --> 00:13:35,570
It So in one case you have a
high spin system with six

174
00:13:35,570 --> 00:13:38,680
water ligands, and then the
other in a low spin system

175
00:13:38,680 --> 00:13:40,930
with six cyanide ligands.

176
00:13:40,930 --> 00:13:43,290
So first, before you do anything
else with this, you

177
00:13:43,290 --> 00:13:46,180
always have to think about
what the d count is.

178
00:13:46,180 --> 00:13:50,320
So, to do the d count, we're
going to look at where iron is

179
00:13:50,320 --> 00:13:53,690
in the periodic table, and
we're going to see

180
00:13:53,690 --> 00:13:56,270
it's in group 8.

181
00:13:56,270 --> 00:14:01,290
And then, we'll have 8 minus
3, the oxidation

182
00:14:01,290 --> 00:14:08,070
number is d 5 system.

183
00:14:08,070 --> 00:14:12,290
So now we have two diagrams
here, one has a big splitting,

184
00:14:12,290 --> 00:14:15,510
one has a small splitting, and
why don't you fill in for me

185
00:14:15,510 --> 00:14:18,590
in a clicker question,
what the high spin

186
00:14:18,590 --> 00:14:19,370
system would look like.

187
00:14:19,370 --> 00:15:15,890
OK, let's just take
10 more seconds.

188
00:15:15,890 --> 00:15:17,540
Very good.

189
00:15:17,540 --> 00:15:20,720
I think that's one of our
highest numbers in a while.

190
00:15:20,720 --> 00:15:23,810
That's right, so we're going to
fill to the fullest extent

191
00:15:23,810 --> 00:15:30,510
possible before we pair
any of the electrons.

192
00:15:30,510 --> 00:15:34,460
So again, here we put in
electrons down here, and then

193
00:15:34,460 --> 00:15:37,310
go up here, because the
splitting is small, so it

194
00:15:37,310 --> 00:15:40,830
doesn't take that much energy
to put an electron in the

195
00:15:40,830 --> 00:15:43,730
upper orbitals, it takes more
energy to pair the electrons

196
00:15:43,730 --> 00:15:45,800
for this weak field system.

197
00:15:45,800 --> 00:15:49,180
And so, this is a high spin
case, we have a maximum number

198
00:15:49,180 --> 00:15:51,060
of unpaired electrons.

199
00:15:51,060 --> 00:15:55,520
So, over here when we have a
much bigger splitting energy,

200
00:15:55,520 --> 00:15:58,340
it's going to take a lot more
energy to put electrons up

201
00:15:58,340 --> 00:16:01,350
there, and so we're going to
fill up all of these orbitals

202
00:16:01,350 --> 00:16:05,110
down here until we have to
put an electron up there.

203
00:16:05,110 --> 00:16:09,680
So, if we do that, put in the
three, and now we're going to

204
00:16:09,680 --> 00:16:12,590
pair, because it takes less
energy to pair than it does to

205
00:16:12,590 --> 00:16:16,280
put an electron up there,
so we do four and five.

206
00:16:16,280 --> 00:16:22,670
And so then here is our system
where we have a strong field,

207
00:16:22,670 --> 00:16:26,230
and so here's a weak field and
it's going to be high spin,

208
00:16:26,230 --> 00:16:28,640
maximum number of unpaired
electrons, here we have the

209
00:16:28,640 --> 00:16:32,510
strong field and it'll be low
spin, the minimum number of

210
00:16:32,510 --> 00:16:35,570
unpaired electrons.

211
00:16:35,570 --> 00:16:39,330
And we're doing this, again,
because we know that cyanide

212
00:16:39,330 --> 00:16:43,910
is a strong field ligand,
whereas water is an

213
00:16:43,910 --> 00:16:45,840
intermediate field
ligand, it's a

214
00:16:45,840 --> 00:16:49,090
lot weaker than cyanide.

215
00:16:49,090 --> 00:16:51,980
OK, now we can continue doing
some of the things that we've

216
00:16:51,980 --> 00:16:52,950
done before.

217
00:16:52,950 --> 00:16:56,520
So just to review this material,
we can write the d n

218
00:16:56,520 --> 00:16:58,460
electron configurations.

219
00:16:58,460 --> 00:17:02,920
What are the orbitals called
that are down here?

220
00:17:02,920 --> 00:17:04,340
Yup, t 2 g.

221
00:17:04,340 --> 00:17:08,620
And how many electrons do
we have there? three.

222
00:17:08,620 --> 00:17:14,110
And then the e g system up
here with two electrons.

223
00:17:14,110 --> 00:17:17,800
And over here what do we have?

224
00:17:17,800 --> 00:17:21,520
Yup, t 2 g to the 5.

225
00:17:21,520 --> 00:17:24,990
So, a review, electron
configurations, these are just

226
00:17:24,990 --> 00:17:28,210
shorthand notations, which
tell people what these

227
00:17:28,210 --> 00:17:32,400
diagrams look like.

228
00:17:32,400 --> 00:17:36,520
Then, we also talked
about this before.

229
00:17:36,520 --> 00:17:42,620
So, what does this
term stand for?

230
00:17:42,620 --> 00:17:47,550
Crystal field stabilization
energy, right.

231
00:17:47,550 --> 00:17:49,610
So now why don't you tell
me what it is for

232
00:17:49,610 --> 00:18:15,260
the high spin system.

233
00:18:15,260 --> 00:18:29,100
OK, let's just take
10 more seconds.

234
00:18:29,100 --> 00:18:34,790
Yup, zero.

235
00:18:34,790 --> 00:18:40,020
So if we look at that, we have
three electrons down here, so

236
00:18:40,020 --> 00:18:44,340
that's minus 2/5, two electrons
up here, which is

237
00:18:44,340 --> 00:18:49,260
plus 3/5, so 3 times minus
2/5 is minus 6/5, plus

238
00:18:49,260 --> 00:18:53,440
6/5 gives you 0.

239
00:18:53,440 --> 00:18:56,540
So here is a case where you
really don't have much

240
00:18:56,540 --> 00:18:58,200
stabilization.

241
00:18:58,200 --> 00:19:02,160
It would be equivalent then, so
there's zero stabilization

242
00:19:02,160 --> 00:19:06,800
because you have three electrons
down and two up.

243
00:19:06,800 --> 00:19:11,220
All right, so what about the
low spin system now?

244
00:19:11,220 --> 00:19:14,290
So if we can look at that, what
are we going to have for

245
00:19:14,290 --> 00:19:18,100
this system?

246
00:19:18,100 --> 00:19:24,580
So, we have 5 times minus 2/5
or minus 10/5, and we also

247
00:19:24,580 --> 00:19:29,160
have two pairing energy terms
there, which we can write in,

248
00:19:29,160 --> 00:19:33,940
because there are two sets
that are paired.

249
00:19:33,940 --> 00:19:38,490
So this is mostly review on what
we've had before, and we

250
00:19:38,490 --> 00:19:40,420
haven't talked about some of
these things in a little

251
00:19:40,420 --> 00:19:43,340
while, so we go over it again,
and now we're going to take it

252
00:19:43,340 --> 00:19:47,270
a next step and think about what
sort of wavelength would

253
00:19:47,270 --> 00:19:50,120
be absorbed if you're going
to promote some of these

254
00:19:50,120 --> 00:19:54,390
electrons to unfilled
orbitals.

255
00:19:54,390 --> 00:19:57,930
So what about the light absorbed
by these octahedral

256
00:19:57,930 --> 00:20:00,280
coordination complexes?

257
00:20:00,280 --> 00:20:02,670
So, if you remember back to the
beginning of the course, a

258
00:20:02,670 --> 00:20:07,560
physics course or high school, a
substance absorbs photons of

259
00:20:07,560 --> 00:20:11,330
light if the energy of the
photons match the energy

260
00:20:11,330 --> 00:20:13,730
required to excite those
electrons to a

261
00:20:13,730 --> 00:20:16,820
higher energy level.

262
00:20:16,820 --> 00:20:20,580
And so now we are doing some
review from the first part of

263
00:20:20,580 --> 00:20:21,940
the course, which
is always good.

264
00:20:21,940 --> 00:20:25,370
As I mentioned, everything kind
of comes together and we

265
00:20:25,370 --> 00:20:28,490
need to go over everything for
the final, but there's also

266
00:20:28,490 --> 00:20:30,270
connections between
all the different

267
00:20:30,270 --> 00:20:32,010
parts of the semester.

268
00:20:32,010 --> 00:20:34,330
So this should look
familiar to you.

269
00:20:34,330 --> 00:20:37,870
So, the energy of the absorbed
light equals Planck's constant

270
00:20:37,870 --> 00:20:40,450
times the frequency
of that light.

271
00:20:40,450 --> 00:20:44,140
But now we can make that equal
to another term, a term we've

272
00:20:44,140 --> 00:20:47,020
been talking about in this
unit, and that is our

273
00:20:47,020 --> 00:20:50,470
octahedral crystal field
splitting energy.

274
00:20:50,470 --> 00:20:53,450
Because the energy that's going
to be required to bump

275
00:20:53,450 --> 00:20:56,960
an electron from here to
here is that energy,

276
00:20:56,960 --> 00:20:58,860
that splitting energy.

277
00:20:58,860 --> 00:21:04,040
So that's going to be equal
to this term here.

278
00:21:04,040 --> 00:21:08,240
OK, so what does this mean in
terms of the wavelengths of

279
00:21:08,240 --> 00:21:14,640
lights absorbed by different
coordination complexes.

280
00:21:14,640 --> 00:21:16,760
So we can think about that.

281
00:21:16,760 --> 00:21:20,550
So if you have high frequency
of light is absorbed, the

282
00:21:20,550 --> 00:21:25,200
wavelength of the absorbed light
is going to be short.

283
00:21:25,200 --> 00:21:28,210
And we know that relationship
-- again, think back to the

284
00:21:28,210 --> 00:21:30,820
beginning of the course and also
probably to physics and

285
00:21:30,820 --> 00:21:34,700
to high school, we know a very
handy equation for telling us

286
00:21:34,700 --> 00:21:38,050
about the relationship of
frequency and wavelength of

287
00:21:38,050 --> 00:21:41,420
light, so we have the speed of
light equals the wavelength

288
00:21:41,420 --> 00:21:43,250
times the frequency.

289
00:21:43,250 --> 00:21:46,220
So if you have a high frequency
of light absorbed,

290
00:21:46,220 --> 00:21:51,560
the absorbed wavelength
is going to be short.

291
00:21:51,560 --> 00:21:54,310
So, let's look at a couple of
examples, the example here,

292
00:21:54,310 --> 00:21:56,140
going back to our example.

293
00:21:56,140 --> 00:21:59,740
So we had this high spin system
with water, and now I'm

294
00:21:59,740 --> 00:22:03,700
telling you that the splitting
energy is 171 kilojoules per

295
00:22:03,700 --> 00:22:09,280
mole, and when you have cyanide
as your ligand, your

296
00:22:09,280 --> 00:22:13,300
splitting energy is 392
kilojoules per mole.

297
00:22:13,300 --> 00:22:15,930
Again, this was a stronger field
ligand, so we have a

298
00:22:15,930 --> 00:22:17,520
bigger splitting energy.

299
00:22:17,520 --> 00:22:21,250
And this was an intermediate
field ligand, certainly weaker

300
00:22:21,250 --> 00:22:25,710
than cyanide, so this has a
smaller splitting energy.

301
00:22:25,710 --> 00:22:29,590
So, from these values now, we
can calculate the wavelength

302
00:22:29,590 --> 00:22:32,710
of absorbed light.

303
00:22:32,710 --> 00:22:36,590
So for the high spin system
first, we can rearrange these

304
00:22:36,590 --> 00:22:40,370
equations, which you know well,
to come up with the

305
00:22:40,370 --> 00:22:43,080
rearranged equation, the
wavelength equals Planck's

306
00:22:43,080 --> 00:22:46,870
constant times the speed of
light, and divided by e, and

307
00:22:46,870 --> 00:22:49,090
this time our e is that crystal

308
00:22:49,090 --> 00:22:51,750
field splitting energy.

309
00:22:51,750 --> 00:22:57,210
So we can put in these terms.
So we have Planck's constant

310
00:22:57,210 --> 00:23:01,700
times the speed of light over
our octahedral field splitting

311
00:23:01,700 --> 00:23:04,920
energy, oh, but then we have
some other terms here.

312
00:23:04,920 --> 00:23:07,970
Now one thing that you have to
pay attention to in this unit

313
00:23:07,970 --> 00:23:09,930
is your units.

314
00:23:09,930 --> 00:23:14,510
So, splitting energies are often
given in kilojoules per

315
00:23:14,510 --> 00:23:18,090
mole, whereas you often see
Planck's constant in joules,

316
00:23:18,090 --> 00:23:20,870
so we want to make sure that we
convert one or the other,

317
00:23:20,870 --> 00:23:22,880
and here it's set up
to convert the

318
00:23:22,880 --> 00:23:25,160
kilojoules to joules.

319
00:23:25,160 --> 00:23:28,600
And also, we want our final
unit, we're talking about

320
00:23:28,600 --> 00:23:32,340
wavelengths, in meters or
nanometers, so we need to get

321
00:23:32,340 --> 00:23:35,630
rid of this mole term,
and we use Avagadro's

322
00:23:35,630 --> 00:23:38,210
number to do that.

323
00:23:38,210 --> 00:23:40,970
So now we should be able to
cancel our units and get the

324
00:23:40,970 --> 00:23:42,100
correct units.

325
00:23:42,100 --> 00:23:47,080
So we should be able to cancel
the seconds over here, and we

326
00:23:47,080 --> 00:23:50,700
should also be able to go
in and cancel our moles.

327
00:23:50,700 --> 00:23:54,980
We should be able to cancel the
joules and the kilojoules

328
00:23:54,980 --> 00:23:59,010
out, and that should leave us
just with this over here,

329
00:23:59,010 --> 00:24:01,470
which is meters.

330
00:24:01,470 --> 00:24:02,690
So this is 7 .

331
00:24:02,690 --> 00:24:06,540
0 0 times 10 to the
minus 7 meters.

332
00:24:06,540 --> 00:24:11,810
Does that make sense in terms
of a wavelength of light?

333
00:24:11,810 --> 00:24:16,260
Because that would convert
to what nanometers?

334
00:24:16,260 --> 00:24:18,850
700 nanometers.

335
00:24:18,850 --> 00:24:22,260
So if you do something strange
and you forget Avagadro's

336
00:24:22,260 --> 00:24:24,970
number, you're going to come
up with a very interesting

337
00:24:24,970 --> 00:24:25,910
wavelength.

338
00:24:25,910 --> 00:24:28,900
So that's a good way to check to
make sure that you've done

339
00:24:28,900 --> 00:24:31,250
the problem correctly.

340
00:24:31,250 --> 00:24:35,650
So, 700 nanometers, anyone
remember what light that is,

341
00:24:35,650 --> 00:24:38,020
what color that corresponds
to?

342
00:24:38,020 --> 00:24:41,030
Red, so it's absorbing
red light.

343
00:24:41,030 --> 00:24:43,930
All right, so now let's just do
the same thing for the low

344
00:24:43,930 --> 00:24:47,700
spin system with the cyanide
ligand, and we're going to

345
00:24:47,700 --> 00:24:55,160
plug in our 392 here, and
we get 305 over here.

346
00:24:55,160 --> 00:25:03,420
And so, that is a much shorter
wavelength of light.

347
00:25:03,420 --> 00:25:07,710
So again, light absorbed for the
compound with water, 700

348
00:25:07,710 --> 00:25:13,080
nanometers, and the compound of
iron with cyanide, 305, and

349
00:25:13,080 --> 00:25:18,580
so we're absorbing a red light
over with the water compound,

350
00:25:18,580 --> 00:25:24,760
and sort of purple or violet
light is being absorbed in the

351
00:25:24,760 --> 00:25:26,480
cyanide complex.

352
00:25:26,480 --> 00:25:29,460
And we're talk in a minute about
the light that is being

353
00:25:29,460 --> 00:25:32,460
transmitted, which is
complementary to the color of

354
00:25:32,460 --> 00:25:35,220
the light absorbed.

355
00:25:35,220 --> 00:25:38,370
So by knowing something about
splitting energies, by knowing

356
00:25:38,370 --> 00:25:42,170
something about the types of
ligands, then you can know

357
00:25:42,170 --> 00:25:45,880
something about colors.

358
00:25:45,880 --> 00:25:49,500
So now, for another example,
we're going to look at the

359
00:25:49,500 --> 00:25:55,890
different colors of two
chromium complexes.

360
00:25:55,890 --> 00:26:00,370
So first, what is the oxidation
number of chromium

361
00:26:00,370 --> 00:26:06,680
in the water complex here?

362
00:26:06,680 --> 00:26:08,470
What is it?

363
00:26:08,470 --> 00:26:12,760
And what about over here
with n h 3 ligands.

364
00:26:12,760 --> 00:26:14,850
Plus 3.

365
00:26:14,850 --> 00:26:18,070
So, plus 3 and plus 3.

366
00:26:18,070 --> 00:26:19,660
And what is our d count?

367
00:26:19,660 --> 00:26:23,900
You know where chromium
is, in what group?

368
00:26:23,900 --> 00:26:24,710
Six.

369
00:26:24,710 --> 00:26:29,790
6 minus 3 is 3, so we
have a d 3 system.

370
00:26:29,790 --> 00:26:32,890
What does c n mean again?

371
00:26:32,890 --> 00:26:37,360
Coordination number, so what
is that for both of these?

372
00:26:37,360 --> 00:26:39,400
Six.

373
00:26:39,400 --> 00:26:42,590
So there's Six things
coordinated to the chromium,

374
00:26:42,590 --> 00:26:48,310
and so we have, again,
an octahedral system.

375
00:26:48,310 --> 00:26:55,960
And what type of ligand
is water?

376
00:26:55,960 --> 00:26:56,990
Intermediate.

377
00:26:56,990 --> 00:27:00,310
And what about n h 3?

378
00:27:00,310 --> 00:27:01,830
Strong.

379
00:27:01,830 --> 00:27:06,600
So this is strong, and water
is and intermediate ligand,

380
00:27:06,600 --> 00:27:10,580
and certainly, it is
weaker than n h 3.

381
00:27:10,580 --> 00:27:14,220
So, we expect one system over
here for a strong ligand, and

382
00:27:14,220 --> 00:27:17,480
then something that's weaker
than that strong ligand.

383
00:27:17,480 --> 00:27:26,580
All right, so here are two
diagrams, one with a big

384
00:27:26,580 --> 00:27:30,820
splitting energy, and one with
a smaller splitting energy.

385
00:27:30,820 --> 00:27:34,640
Are the diagrams going to
look same or different?

386
00:27:34,640 --> 00:27:35,200
The same.

387
00:27:35,200 --> 00:27:39,370
Because we only have three
electrons, so they're going to

388
00:27:39,370 --> 00:27:40,270
be the same.

389
00:27:40,270 --> 00:27:43,720
In both cases, we put in the
three electrons in the lowest

390
00:27:43,720 --> 00:27:46,760
orbitals, and then there's no
decision to be made, because

391
00:27:46,760 --> 00:27:50,755
there isn't that fourth
electron, so we don't have to

392
00:27:50,755 --> 00:27:53,220
decide which place
to put this.

393
00:27:53,220 --> 00:27:56,490
So these diagrams are going to
look the same, and before when

394
00:27:56,490 --> 00:27:59,660
we were doing this in this unit,
we said OK, we're done,

395
00:27:59,660 --> 00:28:00,880
they look the same.

396
00:28:00,880 --> 00:28:04,450
But now, we realize that these
are really not the same

397
00:28:04,450 --> 00:28:06,690
compounds and that they're
going to have different

398
00:28:06,690 --> 00:28:08,920
properties, even though
their diagrams are

399
00:28:08,920 --> 00:28:10,280
going to look the same.

400
00:28:10,280 --> 00:28:13,460
Because the energy that it's
going to take to excite an

401
00:28:13,460 --> 00:28:17,540
electron here is much smaller
than over here, and that's

402
00:28:17,540 --> 00:28:20,540
going to result in a different
wavelength of light being

403
00:28:20,540 --> 00:28:23,240
absorbed in these two different
cases, which will

404
00:28:23,240 --> 00:28:28,540
mean a different wavelength of
light being transmitted.

405
00:28:28,540 --> 00:28:32,370
So, again, here we have a weaker
field and here we have

406
00:28:32,370 --> 00:28:35,730
a stronger field.

407
00:28:35,730 --> 00:28:37,980
So again, we can go
through and think

408
00:28:37,980 --> 00:28:40,770
about these two cases.

409
00:28:40,770 --> 00:28:44,760
So when we have a smaller term
here, that means a lower

410
00:28:44,760 --> 00:28:47,940
energy -- this is a splitting
energy, and so we'll have a

411
00:28:47,940 --> 00:28:49,610
lower frequency.

412
00:28:49,610 --> 00:28:54,060
When we have a larger case or
higher energy, we have a

413
00:28:54,060 --> 00:28:57,950
higher frequency.

414
00:28:57,950 --> 00:29:02,000
Again, if you have a lower
frequency absorbed, we have a

415
00:29:02,000 --> 00:29:06,370
longer wavelength absorbed, and
in this case, the higher

416
00:29:06,370 --> 00:29:12,300
frequency translates into a
shorter wavelength absorbed.

417
00:29:12,300 --> 00:29:15,500
The color of the transmitted
light is complementary to the

418
00:29:15,500 --> 00:29:18,940
color of the absorbed light.

419
00:29:18,940 --> 00:29:21,600
So now we can think about --

420
00:29:21,600 --> 00:29:25,180
I always want to ask, when
do people learn about

421
00:29:25,180 --> 00:29:26,520
complementary colors?

422
00:29:26,520 --> 00:29:33,650
Is that 6th grade, earlier?

423
00:29:33,650 --> 00:29:38,410
I don't really remember, but I
think it's pretty early on.

424
00:29:38,410 --> 00:29:42,080
And people always ask me, are
you going to have that on the

425
00:29:42,080 --> 00:29:45,190
equation sheet, or do I have
to actually remember my

426
00:29:45,190 --> 00:29:46,900
complementary colors?

427
00:29:46,900 --> 00:29:51,210
And I tell people that I will
put some version of this on,

428
00:29:51,210 --> 00:29:58,480
so you don't have to review your
kindergarten notes for

429
00:29:58,480 --> 00:30:00,400
this class, if that's
when you learned it.

430
00:30:00,400 --> 00:30:05,220
It's pretty early, I don't
know when it is exactly.

431
00:30:05,220 --> 00:30:08,950
So, the color of the light is
going to be complementary

432
00:30:08,950 --> 00:30:14,090
about -- this is very
approximate.

433
00:30:14,090 --> 00:30:19,190
So here, if the transmitted
light is shorter because we

434
00:30:19,190 --> 00:30:24,000
have this weaker splitting, then
we are expecting we're

435
00:30:24,000 --> 00:30:26,360
going to have this shorter
wavelength, the transmitted

436
00:30:26,360 --> 00:30:30,080
light, and experimentally, if
you make this compound you'll

437
00:30:30,080 --> 00:30:31,620
see it's violet.

438
00:30:31,620 --> 00:30:35,080
In this other case, we have a
stronger field ligand, and so

439
00:30:35,080 --> 00:30:38,850
you have a larger energy, higher
frequency absorbed,

440
00:30:38,850 --> 00:30:41,780
shorter wavelength absorbed,
then you're going to have a

441
00:30:41,780 --> 00:30:44,740
longer wavelength from your
transmitted light.

442
00:30:44,740 --> 00:30:48,780
And that this compound, if you
make it, is actually yellow.

443
00:30:48,780 --> 00:30:52,990
So if we go back to our colors
for a minute, you see that

444
00:30:52,990 --> 00:30:55,540
when you have the shorter
wavelength, we have a violet,

445
00:30:55,540 --> 00:30:58,170
and that is a short
wavelength.

446
00:30:58,170 --> 00:31:03,060
And in this case for the strong
field ligand, we are

447
00:31:03,060 --> 00:31:05,510
going to have transmitted light
of a longer wavelength

448
00:31:05,510 --> 00:31:07,030
and it's yellow.

449
00:31:07,030 --> 00:31:11,230
So it's the same oxidation state
of chromium, it's the

450
00:31:11,230 --> 00:31:15,460
same -- it's an octahedral
complex, six ligands in both

451
00:31:15,460 --> 00:31:20,590
cases, same octahedral crystal
field diagrams, but yet one

452
00:31:20,590 --> 00:31:23,400
compound has a violet color,
and the other one

453
00:31:23,400 --> 00:31:30,220
has a yellow color.

454
00:31:30,220 --> 00:31:35,250
All right, so one can also be
asked to calculate a crystal

455
00:31:35,250 --> 00:31:39,100
field splitting energy in
kilojoules per mole, given the

456
00:31:39,100 --> 00:31:41,030
appropriate information.

457
00:31:41,030 --> 00:31:45,070
So we've looked at when a
splitting energy is given, and

458
00:31:45,070 --> 00:31:48,570
we've been asked to calculate
wavelength absorbed, you can

459
00:31:48,570 --> 00:31:52,190
also be asked to go in
the other direction.

460
00:31:52,190 --> 00:31:55,670
And so here we have another
chromium complex to work with.

461
00:31:55,670 --> 00:31:57,990
And we're told that the
wavelength of the most

462
00:31:57,990 --> 00:32:04,660
intensely absorbed light is
740, and so what would you

463
00:32:04,660 --> 00:32:10,170
predict the color
of this to be?

464
00:32:10,170 --> 00:32:12,560
It would be greenish.

465
00:32:12,560 --> 00:32:14,230
So that would be what
you would predict.

466
00:32:14,230 --> 00:32:17,870
Again, chemistry is an
experimental science, but

467
00:32:17,870 --> 00:32:21,350
based on having a complementary
color to the one

468
00:32:21,350 --> 00:32:22,990
absorbed, that would
be a guess.

469
00:32:22,990 --> 00:32:32,000
All right, so we can actually
calculate the frequency of the

470
00:32:32,000 --> 00:32:34,790
light absorbed.

471
00:32:34,790 --> 00:32:38,060
So we were given the wavelength,
and use speed of

472
00:32:38,060 --> 00:32:41,070
light, and plug in your
wavelength and you can come up

473
00:32:41,070 --> 00:32:48,570
with a frequency, 4.05 times
10 to the 14 per second.

474
00:32:48,570 --> 00:32:51,340
Then we can calculate from
that the crystal field

475
00:32:51,340 --> 00:32:55,490
splitting energy, and so we use
Planck's constant, and we

476
00:32:55,490 --> 00:32:59,080
have our frequency, and
we calculate 2 .

477
00:32:59,080 --> 00:33:02,460
6 8 times 10 to the
minus 19 joules.

478
00:33:02,460 --> 00:33:07,580
Am I done with the problem?

479
00:33:07,580 --> 00:33:09,110
What does the problem ask for?

480
00:33:09,110 --> 00:33:15,470
It asks for it in kilojoules
per mole, and so, we're not

481
00:33:15,470 --> 00:33:18,010
done, we need to convert
to kilojoules per mole.

482
00:33:18,010 --> 00:33:20,680
And I'm making this point,
because often this is where

483
00:33:20,680 --> 00:33:24,070
people lose points on the final
exam, and that's not

484
00:33:24,070 --> 00:33:25,370
where you want to lose points.

485
00:33:25,370 --> 00:33:28,210
You want to lose them on a
really hard problem, not on

486
00:33:28,210 --> 00:33:29,570
something like this.

487
00:33:29,570 --> 00:33:33,160
So, most of the time you're
asked for kilojoules per mole,

488
00:33:33,160 --> 00:33:36,190
so make sure that if that's what
asked for, that's what

489
00:33:36,190 --> 00:33:37,490
you provide.

490
00:33:37,490 --> 00:33:41,730
So here, we can just do the
conversion of units, and then

491
00:33:41,730 --> 00:33:43,790
we're going to use Avagadro's
number to

492
00:33:43,790 --> 00:33:45,770
give us that per mole.

493
00:33:45,770 --> 00:33:49,880
And so, this translates into a
160 kilojoules per mole, which

494
00:33:49,880 --> 00:33:52,840
you might recognize is more
similar to the other numbers

495
00:33:52,840 --> 00:33:55,090
that you saw for octahedral
crystal

496
00:33:55,090 --> 00:34:00,050
field splitting energy.

497
00:34:00,050 --> 00:34:01,990
All right.

498
00:34:01,990 --> 00:34:07,130
Sadly, there are some
coordination complexes that do

499
00:34:07,130 --> 00:34:11,710
not have colors.

500
00:34:11,710 --> 00:34:19,290
Why would that be?

501
00:34:19,290 --> 00:34:21,960
Why would something
not have a color?

502
00:34:21,960 --> 00:34:32,050
It has d orbitals, it's
a transition metal.

503
00:34:32,050 --> 00:34:34,390
So what would be true about
all of the d orbitals?

504
00:34:34,390 --> 00:34:43,170
Yeah, so one example, is if
they're all full, and that is

505
00:34:43,170 --> 00:34:46,200
the most common thing that we
see, so it's not possible to

506
00:34:46,200 --> 00:34:51,500
have a d to d transition
in the visible range.

507
00:34:51,500 --> 00:34:54,140
So there are a number of
examples of metals who have

508
00:34:54,140 --> 00:34:56,590
this situation.

509
00:34:56,590 --> 00:35:01,960
Zinc and cadmium are two of the
most common that give you

510
00:35:01,960 --> 00:35:06,210
problems in biological systems.
So why is this?

511
00:35:06,210 --> 00:35:11,160
Well, that's because they're
over here in group twelve.

512
00:35:11,160 --> 00:35:15,470
But their most common oxidation
states are plus 2.

513
00:35:15,470 --> 00:35:21,300
So, if you have 12 minus 2 you
have a d 10 system, and that's

514
00:35:21,300 --> 00:35:24,310
the case for both of
these systems here.

515
00:35:24,310 --> 00:35:27,080
And so all the d orbitals
are filled.

516
00:35:27,080 --> 00:35:31,280
Now, zinc is a really important
metal in biological

517
00:35:31,280 --> 00:35:37,620
systems, and because it has all
these d orbitals filled,

518
00:35:37,620 --> 00:35:38,950
it doesn't have a color.

519
00:35:38,950 --> 00:35:43,670
And so it's very hard to tell
if an enzyme molecule has

520
00:35:43,670 --> 00:35:47,100
zinc. And I think one of the
problems that you have on this

521
00:35:47,100 --> 00:35:50,160
problem-set talks about how
zinc is important in a

522
00:35:50,160 --> 00:35:54,700
biological system by altering
the p k a of a residue that

523
00:35:54,700 --> 00:35:56,140
coordinates to it.

524
00:35:56,140 --> 00:36:01,130
And that's often its job, and so
biochemists are often faced

525
00:36:01,130 --> 00:36:03,820
with the problem of trying to
figure out if their protein

526
00:36:03,820 --> 00:36:07,890
has zinc, but they have no color
of the protein, also

527
00:36:07,890 --> 00:36:10,590
they might try to look
for a paramagnetic

528
00:36:10,590 --> 00:36:12,460
or diamagnetic system.

529
00:36:12,460 --> 00:36:14,960
They're not -- you know if
they see a paramagnetic

530
00:36:14,960 --> 00:36:17,980
system, they say oh, unpaired
electrons, we know we must

531
00:36:17,980 --> 00:36:20,820
have metal involved, but
there's no sort of

532
00:36:20,820 --> 00:36:23,120
spectroscopic probe for zinc.

533
00:36:23,120 --> 00:36:26,720
And so, often someone will
determine a crystal structure,

534
00:36:26,720 --> 00:36:30,160
and it'll be a huge surprise
that there's zinc associated

535
00:36:30,160 --> 00:36:32,760
with this protein.

536
00:36:32,760 --> 00:36:36,400
Do you think there's a lot of
proteins that use cadmium as

537
00:36:36,400 --> 00:36:39,860
of part of their mechanism?

538
00:36:39,860 --> 00:36:42,210
What do you know
about cadmium?

539
00:36:42,210 --> 00:36:44,260
Yeah, cadmium is poisonous.

540
00:36:44,260 --> 00:36:47,560
Old barbecue grills were
sometimes, they used to coat

541
00:36:47,560 --> 00:36:50,570
things with cadmium on
a barbecue grill.

542
00:36:50,570 --> 00:36:54,060
Yeah, that was not very smart.

543
00:36:54,060 --> 00:36:56,690
So, cadmium poisoning is a
problem, and people have been

544
00:36:56,690 --> 00:36:59,010
trying to figure out the
mechanism of that, but again,

545
00:36:59,010 --> 00:37:01,570
it's hard to study cadmium
because it has no

546
00:37:01,570 --> 00:37:07,050
spectroscopic signal.

547
00:37:07,050 --> 00:37:13,170
All right, so getting back now
to just kind of review over

548
00:37:13,170 --> 00:37:16,640
what we've talked about
in terms of colors.

549
00:37:16,640 --> 00:37:19,120
So we have our weak field
ligands, again, you need to

550
00:37:19,120 --> 00:37:20,790
memorize what they are.

551
00:37:20,790 --> 00:37:23,140
You have your intermediate field
ligands, which you need

552
00:37:23,140 --> 00:37:27,270
to memorize, and also your
strong field ligands.

553
00:37:27,270 --> 00:37:29,860
So these weak field ligands
are going to have a small

554
00:37:29,860 --> 00:37:33,700
splitting energy, and that means
that in terms of how the

555
00:37:33,700 --> 00:37:37,510
complex absorbs, low energy,
low frequency, long

556
00:37:37,510 --> 00:37:40,780
wavelength, and that the color
transmitted will be

557
00:37:40,780 --> 00:37:41,950
complementary.

558
00:37:41,950 --> 00:37:48,180
And usually what this means is
that it'll be sort of in the

559
00:37:48,180 --> 00:37:51,360
end of the spectra, so it's
often hard to say well, red

560
00:37:51,360 --> 00:37:53,740
will definitely be green.

561
00:37:53,740 --> 00:37:57,530
So it's not a perfect agreement,
but you can usually

562
00:37:57,530 --> 00:37:59,090
say well, it's probably
going to be in the

563
00:37:59,090 --> 00:38:00,920
blue-violet or green end.

564
00:38:00,920 --> 00:38:05,540
So in sort of one part
of the spectra.

565
00:38:05,540 --> 00:38:08,760
Strong field ligands, again,
have a huge splitting energy.

566
00:38:08,760 --> 00:38:11,200
So you're going to have big
energy, high frequency, short

567
00:38:11,200 --> 00:38:14,930
wavelength, and so it's going
to transmit, then, in the

568
00:38:14,930 --> 00:38:17,360
complementary, so it should
be in the yellow,

569
00:38:17,360 --> 00:38:19,380
orange or red end.

570
00:38:19,380 --> 00:38:22,250
And you will be asked in some
of the problems, in again,

571
00:38:22,250 --> 00:38:25,330
problem-set 9 due Wednesday,
and you should be able to

572
00:38:25,330 --> 00:38:28,250
finish that up pretty quickly
tonight after this lecture,

573
00:38:28,250 --> 00:38:30,980
and there are some
problems on this.

574
00:38:30,980 --> 00:38:37,200
So, for cobalt complexes, you
get pretty much the entire

575
00:38:37,200 --> 00:38:39,270
range of colors.

576
00:38:39,270 --> 00:38:44,330
So I'm just going to end with
one more biological example.

577
00:38:44,330 --> 00:38:49,910
And here are some pictures of
actual colors, and so this is

578
00:38:49,910 --> 00:38:53,870
cobalt coordinated
to vitamin B12.

579
00:38:53,870 --> 00:38:57,570
So one ligand gives you this
brilliant red color, another

580
00:38:57,570 --> 00:39:01,140
gives you an orange color, and
a third ligand gives you a

581
00:39:01,140 --> 00:39:02,300
pink color.

582
00:39:02,300 --> 00:39:06,910
So you can tell the oxidation
state of vitamin B12 by the

583
00:39:06,910 --> 00:39:10,840
colors of the molecule.

584
00:39:10,840 --> 00:39:12,100
All right.

585
00:39:12,100 --> 00:39:14,890
Now you have all the information
to finish your

586
00:39:14,890 --> 00:39:18,950
problem-set, and that's the
end of transition metals.

587
00:39:18,950 --> 00:39:21,620
On Wednesday we start
kinetics.