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CATHERINE DRENNAN: And
so on today's hand out

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00:00:29,530 --> 00:00:31,900
we're continuing to
think about color.

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00:00:31,900 --> 00:00:34,690
We're also going to think
about magnetism some more,

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00:00:34,690 --> 00:00:38,210
and we're going to think about
more types of geometries.

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00:00:38,210 --> 00:00:41,440
So we've seen that the type
of ligand, whether it's

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00:00:41,440 --> 00:00:44,230
a weak field, intermediate
field, or strong field ligand

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00:00:44,230 --> 00:00:46,870
makes a difference in terms
of the splitting energy.

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00:00:46,870 --> 00:00:49,360
How much the d
orbitals are split due

16
00:00:49,360 --> 00:00:51,070
in the presence of
the ligand, arranged

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00:00:51,070 --> 00:00:52,900
in octahedron geometry.

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00:00:52,900 --> 00:00:54,994
But we'll see that
the geometry matters.

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00:00:54,994 --> 00:00:57,160
That if you have different
kinds of geometries, then

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00:00:57,160 --> 00:00:58,743
the splinting is
going to be different

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00:00:58,743 --> 00:01:00,340
between the d orbitals.

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00:01:00,340 --> 00:01:04,060
So now we're going to
look-- and I'll set this up.

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00:01:04,060 --> 00:01:06,114
We're going to look at
a nickel demo, which

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00:01:06,114 --> 00:01:07,280
we'll have in a few minutes.

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00:01:07,280 --> 00:01:10,450
But first, let's think about the
colors that we're going to see.

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00:01:10,450 --> 00:01:16,060
So if we have a nickel chloride
compound that is greenish,

27
00:01:16,060 --> 00:01:19,930
what kind-- it will absorb
then what kind of light,

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00:01:19,930 --> 00:01:21,760
if it is a greenish
kind of color?

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00:01:21,760 --> 00:01:23,740
What color would it absorb then?

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00:01:23,740 --> 00:01:24,520
AUDIENCE: Red.

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00:01:24,520 --> 00:01:25,030
CATHERINE DRENNAN: Red.

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00:01:25,030 --> 00:01:27,010
Reddish, which is what
kind of wavelength?

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00:01:27,010 --> 00:01:28,140
Long or short?

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00:01:28,140 --> 00:01:28,900
AUDIENCE: Long.

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00:01:28,900 --> 00:01:29,350
CATHERINE DRENNAN: Long.

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00:01:29,350 --> 00:01:29,849
Right.

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00:01:29,849 --> 00:01:32,570
So we're going to get a
long, reddish kind of-- it

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00:01:32,570 --> 00:01:35,960
will absorb a long
or red wavelength.

39
00:01:35,960 --> 00:01:38,659
And so if we're absorbing
a long wavelength, what

40
00:01:38,659 --> 00:01:40,450
would be true about
the splitting energies?

41
00:01:40,450 --> 00:01:44,800
Is it going to be a big
or small splitting energy?

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00:01:44,800 --> 00:01:47,140
So first, if you
have long wavelength

43
00:01:47,140 --> 00:01:48,430
what's the frequency?

44
00:01:48,430 --> 00:01:49,334
Long or short?

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00:01:49,334 --> 00:01:50,000
AUDIENCE: Short.

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00:01:50,000 --> 00:01:51,041
CATHERINE DRENNAN: Short.

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00:01:51,041 --> 00:01:53,830
And so the energy
would be short as well.

48
00:01:53,830 --> 00:01:58,020
So it's going to be a small
energy associated with it.

49
00:01:58,020 --> 00:01:59,980
Just a small splitting.

50
00:01:59,980 --> 00:02:03,010
And you remember what we
learned about chloride minus?

51
00:02:03,010 --> 00:02:05,320
What kind of a ligand is it?

52
00:02:05,320 --> 00:02:07,660
It's a weak field ligand,
so this makes sense.

53
00:02:07,660 --> 00:02:10,479
So a weak field ligand only
splits the field a little bit,

54
00:02:10,479 --> 00:02:12,430
it's not a very strong
ligand, so it can only

55
00:02:12,430 --> 00:02:15,040
split it so much.

56
00:02:15,040 --> 00:02:19,000
Now we're going to take
this greenish compound

57
00:02:19,000 --> 00:02:21,940
and we're going to
add some water to it.

58
00:02:21,940 --> 00:02:25,310
And that's going to make
it a little more blue.

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00:02:25,310 --> 00:02:27,430
Be sort of a blue green.

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00:02:27,430 --> 00:02:31,000
And let's think about
what's happening there.

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00:02:31,000 --> 00:02:33,490
And we'll compare it
to what we have above.

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00:02:33,490 --> 00:02:37,330
So now, if it looks blue
green, what sort of color

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00:02:37,330 --> 00:02:38,945
is going to be what's absorbed?

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00:02:38,945 --> 00:02:39,820
AUDIENCE: Orange red.

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00:02:39,820 --> 00:02:40,861
CATHERINE DRENNAN: Right.

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00:02:40,861 --> 00:02:44,930
So we're going to have a
more orange red color here.

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00:02:44,930 --> 00:02:49,060
And so that's going to be longer
or shorter than the one above?

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AUDIENCE: Shorter.

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00:02:49,960 --> 00:02:50,680
CATHERINE DRENNAN: Shorter.

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Right.

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So we were here.

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00:02:52,150 --> 00:02:54,417
Now we're moving more
into the orange region,

73
00:02:54,417 --> 00:02:56,500
so we're going to be
absorbing a wavelength that's

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00:02:56,500 --> 00:02:57,710
a bit shorter.

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00:02:57,710 --> 00:03:01,580
So is the energy going
to be larger or smaller?

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00:03:01,580 --> 00:03:02,080
Yeah.

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00:03:02,080 --> 00:03:04,624
So it's going to be a
larger energy because we

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00:03:04,624 --> 00:03:06,040
have a shorter
wavelength so we're

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00:03:06,040 --> 00:03:07,850
going to have a bit
of a higher frequency.

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00:03:07,850 --> 00:03:10,719
And so we'll have a higher
energy or larger energy.

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00:03:10,719 --> 00:03:12,760
And do you remember what
kind of ligand water is?

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It's an intermediate
field ligand

83
00:03:18,199 --> 00:03:19,990
so it's going to be
stronger than chloride.

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00:03:19,990 --> 00:03:21,340
So chloride was very weak.

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00:03:21,340 --> 00:03:22,930
Water sort of in the middle.

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00:03:22,930 --> 00:03:25,690
And then we had cyanide as an
example of a very strong field

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00:03:25,690 --> 00:03:27,390
ligand.

88
00:03:27,390 --> 00:03:30,100
So this makes sense that
would be a bit stronger.

89
00:03:30,100 --> 00:03:32,080
So we have a larger splitting.

90
00:03:32,080 --> 00:03:34,810
Now they're going to break
this sample into two.

91
00:03:34,810 --> 00:03:38,380
And batch one you're
going to add EDTA.

92
00:03:38,380 --> 00:03:42,040
That was our chelating agent
that we talked about before,

93
00:03:42,040 --> 00:03:44,680
and that's going to make
it even a bit more blue.

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00:03:44,680 --> 00:03:48,700
And here we have our model
of EDTA bound to our metal.

95
00:03:48,700 --> 00:03:51,460
And so if we think
about this, then

96
00:03:51,460 --> 00:03:53,980
if it's a bit more
blue-- so we're

97
00:03:53,980 --> 00:03:57,940
going to be absorbing a color
that's even more orange.

98
00:03:57,940 --> 00:04:02,120
And so that's going to be even
shorter than what we had there.

99
00:04:02,120 --> 00:04:07,180
So then our splitting energy--
the energy is going to be what?

100
00:04:07,180 --> 00:04:08,925
Larger or smaller?

101
00:04:08,925 --> 00:04:09,841
AUDIENCE: [INAUDIBLE].

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00:04:09,841 --> 00:04:10,840
CATHERINE DRENNAN: Yeah.

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00:04:10,840 --> 00:04:12,100
So it will be even larger.

104
00:04:12,100 --> 00:04:15,310
And I've never told you
what kind of ligand EDTA is,

105
00:04:15,310 --> 00:04:18,190
but from this, if you're
getting a larger splitting,

106
00:04:18,190 --> 00:04:21,130
you would predict it's a
stronger ligand than water.

107
00:04:21,130 --> 00:04:24,880
And in fact it is an even
stronger one than water.

108
00:04:24,880 --> 00:04:28,420
And again, we're going to be
increasing entropy in this room

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00:04:28,420 --> 00:04:30,160
in a few minutes
because we're going

110
00:04:30,160 --> 00:04:33,340
to be displacing six
water molecules with one

111
00:04:33,340 --> 00:04:35,860
molecule of EDTA, which
will bind to your metal

112
00:04:35,860 --> 00:04:37,300
with six points of attachment.

113
00:04:37,300 --> 00:04:40,150
So watch out for
that entropy change.

114
00:04:40,150 --> 00:04:41,980
So that was batch one.

115
00:04:41,980 --> 00:04:48,550
Now we're going to take some of
this nickel hexa-aquo compound

116
00:04:48,550 --> 00:04:51,070
and we're going to mix it
with another chelating agent.

117
00:04:51,070 --> 00:04:55,030
So remember, our nickel
water complex is blue green

118
00:04:55,030 --> 00:04:57,790
and we're going to add
another chelating agent,

119
00:04:57,790 --> 00:05:00,430
and now it's going
to become red.

120
00:05:00,430 --> 00:05:05,084
And so if it's red, what
color is going to be absorbed?

121
00:05:05,084 --> 00:05:05,750
AUDIENCE: Green.

122
00:05:05,750 --> 00:05:06,940
CATHERINE DRENNAN: Green.

123
00:05:06,940 --> 00:05:08,980
And so this wavelength
then is going

124
00:05:08,980 --> 00:05:12,330
to be what compared to orange?

125
00:05:12,330 --> 00:05:14,670
Yeah, so it's even way shorter.

126
00:05:14,670 --> 00:05:15,970
We were kind of right up here.

127
00:05:15,970 --> 00:05:19,790
Now we've all the way shifted
down here so it's way shorter.

128
00:05:19,790 --> 00:05:21,970
So the energy is
going to be what?

129
00:05:21,970 --> 00:05:23,630
Small or big?

130
00:05:23,630 --> 00:05:24,366
AUDIENCE: Big.

131
00:05:24,366 --> 00:05:26,240
CATHERINE DRENNAN: It's
going to be very big.

132
00:05:26,240 --> 00:05:29,200
But this isn't an
octahedral system anymore,

133
00:05:29,200 --> 00:05:32,530
so I didn't have a
little O by my energy.

134
00:05:32,530 --> 00:05:34,960
And it's actually a
square planar system

135
00:05:34,960 --> 00:05:38,060
so we're not gonna do sort
of a direct comparison here.

136
00:05:38,060 --> 00:05:40,690
But this tells us
that in square planar

137
00:05:40,690 --> 00:05:42,940
you're probably going to
get pretty big splitting

138
00:05:42,940 --> 00:05:46,090
of our d orbital energies
because we can get something

139
00:05:46,090 --> 00:05:50,710
that-- the color suggests that
there must be a big splitting.

140
00:05:50,710 --> 00:05:54,490
So those are what we're
predicting for the colors.

141
00:05:54,490 --> 00:05:55,450
Let's see what happens.

142
00:06:04,281 --> 00:06:05,280
GUEST SPEAKER: Is it on?

143
00:06:05,280 --> 00:06:05,640
Yes it is.

144
00:06:05,640 --> 00:06:06,140
OK.

145
00:06:06,140 --> 00:06:08,430
So this is the nickel
chloride complex

146
00:06:08,430 --> 00:06:09,760
that Cathy was talking about.

147
00:06:09,760 --> 00:06:12,470
As most of us can
see it's very green.

148
00:06:12,470 --> 00:06:13,350
Put it under here.

149
00:06:13,350 --> 00:06:16,290
You could probably obviously
see that it's green.

150
00:06:16,290 --> 00:06:17,895
Maybe against this background.

151
00:06:17,895 --> 00:06:18,700
Look at that.

152
00:06:18,700 --> 00:06:19,380
It's very green.

153
00:06:19,380 --> 00:06:22,570
Thank you, Elena.

154
00:06:22,570 --> 00:06:24,002
So we don't need that, do we?

155
00:06:24,002 --> 00:06:24,960
No, we don't need that.

156
00:06:24,960 --> 00:06:26,626
We're just gonna pour
it into the water.

157
00:06:26,626 --> 00:06:32,220
So when we pour this
into the water we're

158
00:06:32,220 --> 00:06:34,010
expecting-- you guys remember?

159
00:06:34,010 --> 00:06:35,010
Blue green.

160
00:06:35,010 --> 00:06:38,010
So [INAUDIBLE].

161
00:06:42,440 --> 00:06:51,804
And that's fuming.

162
00:07:00,671 --> 00:07:01,171
That smells.

163
00:07:01,171 --> 00:07:01,671
Terrible.

164
00:07:05,640 --> 00:07:09,054
And that's very
obviously not that clear.

165
00:07:09,054 --> 00:07:11,440
[LAUGHTER]

166
00:07:11,440 --> 00:07:12,060
Wonderful.

167
00:07:12,060 --> 00:07:14,826
Well, it's kind of blue green.

168
00:07:14,826 --> 00:07:17,200
Right around the color that
you'd expect for water to be.

169
00:07:17,200 --> 00:07:18,210
CATHERINE DRENNAN: We
should switch gloves

170
00:07:18,210 --> 00:07:20,802
from green to blue green
as we do the experiment.

171
00:07:20,802 --> 00:07:22,760
You can see it a little
bit better there maybe.

172
00:07:22,760 --> 00:07:24,290
I don't know.

173
00:07:24,290 --> 00:07:25,320
Trust us.

174
00:07:25,320 --> 00:07:26,010
GUEST SPEAKER: Now
we're going to do--

175
00:07:26,010 --> 00:07:28,385
CATHERINE DRENNAN: The next
one's a little more dramatic.

176
00:07:28,385 --> 00:07:30,187
Front row.

177
00:07:30,187 --> 00:07:31,710
Is it blue green?

178
00:07:31,710 --> 00:07:33,274
AUDIENCE: Yeah.

179
00:07:33,274 --> 00:07:35,190
GUEST SPEAKER: So we're
going to split this up

180
00:07:35,190 --> 00:07:39,930
into two solutions,
which is about 180 mls.

181
00:07:42,855 --> 00:07:44,813
I should have picked a
different colored glove.

182
00:07:50,470 --> 00:07:53,030
And we're going to add
some EDTA-- thank you.

183
00:07:53,030 --> 00:07:55,540
We're going to add
some EDTA into this.

184
00:07:55,540 --> 00:07:57,430
And that EDTA is where?

185
00:07:57,430 --> 00:07:58,700
It's a powder, right?

186
00:07:58,700 --> 00:08:01,021
So EDTA is relatively
insoluble in water

187
00:08:01,021 --> 00:08:02,770
so we're going to add
a little bit of base

188
00:08:02,770 --> 00:08:04,360
to make sure this works.

189
00:08:04,360 --> 00:08:06,510
That's not the base.

190
00:08:06,510 --> 00:08:08,180
That's the base.

191
00:08:08,180 --> 00:08:09,910
So let's start with the EDTA.

192
00:08:09,910 --> 00:08:12,965
I'm gonna use this
to mix, I think.

193
00:08:12,965 --> 00:08:14,323
I should mix it with this.

194
00:08:19,037 --> 00:08:20,993
I should have gotten
something to mix it with.

195
00:08:23,930 --> 00:08:26,350
I don't think so.

196
00:08:26,350 --> 00:08:26,850
Watch out.

197
00:08:26,850 --> 00:08:27,130
Watch out.

198
00:08:27,130 --> 00:08:28,588
This is going to
be a bit reactive.

199
00:08:36,312 --> 00:08:38,123
It worked pretty well, actually.

200
00:08:38,123 --> 00:08:40,062
Look at that.

201
00:08:40,062 --> 00:08:40,874
Yay.

202
00:08:40,874 --> 00:08:41,730
It's blue.

203
00:08:45,175 --> 00:08:46,140
Just a second.

204
00:08:46,140 --> 00:08:48,540
[LAUGHTER]

205
00:08:48,540 --> 00:08:53,830
So by comparison it's
a little bit more blue.

206
00:08:53,830 --> 00:08:57,700
And as we added some
hydroxide-- or not hydroxide,

207
00:08:57,700 --> 00:09:01,090
acetate-- it allowed the EDTA
to dissolve just a little bit

208
00:09:01,090 --> 00:09:03,100
more, which is why it reacted.

209
00:09:03,100 --> 00:09:03,820
OK, cool.

210
00:09:03,820 --> 00:09:12,200
So now for the last thing we
will add-- what are we adding?

211
00:09:12,200 --> 00:09:12,700
Oh, right.

212
00:09:12,700 --> 00:09:13,222
DMG.

213
00:09:13,222 --> 00:09:15,430
And we apologize to Cathy
because this smells really,

214
00:09:15,430 --> 00:09:18,009
really bad and she has to smell
this for the next 20 minutes

215
00:09:18,009 --> 00:09:19,050
along with the front row.

216
00:09:19,050 --> 00:09:20,383
AUDIENCE: So will the front row.

217
00:09:20,383 --> 00:09:21,440
GUEST SPEAKER: Sorry.

218
00:09:21,440 --> 00:09:24,236
But after we pour this
you're not actually

219
00:09:24,236 --> 00:09:25,944
going to see a whole
lot of color change.

220
00:09:29,970 --> 00:09:31,890
It smell bad.

221
00:09:31,890 --> 00:09:35,640
And the reason for that
is because this is not

222
00:09:35,640 --> 00:09:36,970
quite as good.

223
00:09:36,970 --> 00:09:41,110
So the DMG has to come in and
actually replace the water,

224
00:09:41,110 --> 00:09:43,444
and it's actually kind of
hard for DMG to replace water.

225
00:09:43,444 --> 00:09:45,026
So what we're going
to do now is we're

226
00:09:45,026 --> 00:09:46,530
going to add a bit of ammonia.

227
00:09:46,530 --> 00:09:48,490
And the ammonia can
replace the water

228
00:09:48,490 --> 00:09:51,870
a little better
than the DMG can,

229
00:09:51,870 --> 00:09:53,740
and the DMG is going
to replace the ammonia.

230
00:09:53,740 --> 00:09:55,323
And you'll see
something kind of cool.

231
00:09:55,323 --> 00:09:58,260
It's actually going to
very locally change color,

232
00:09:58,260 --> 00:10:01,040
and I might actually do this.

233
00:10:01,040 --> 00:10:02,080
Maybe over here.

234
00:10:02,080 --> 00:10:03,710
CATHERINE DRENNAN: What to
do it on the document camera?

235
00:10:03,710 --> 00:10:04,747
GUEST SPEAKER: Is going
to work on the camera?

236
00:10:04,747 --> 00:10:05,705
CATHERINE DRENNAN: Mhm.

237
00:10:05,705 --> 00:10:06,940
GUEST SPEAKER: OK.

238
00:10:06,940 --> 00:10:09,970
And let's give this a shot.

239
00:10:09,970 --> 00:10:11,640
Well, I can't reach that.

240
00:10:16,844 --> 00:10:18,760
CATHERINE DRENNAN: You
have to move your hand.

241
00:10:18,760 --> 00:10:19,690
GUEST SPEAKER: Let me pour it.

242
00:10:19,690 --> 00:10:21,940
CATHERINE DRENNAN: Yeah, so
you can see the local now.

243
00:10:26,020 --> 00:10:29,490
GUEST SPEAKER: So it goes
back to being blue green again

244
00:10:29,490 --> 00:10:32,550
because the concentration
of ammonia that we're adding

245
00:10:32,550 --> 00:10:36,452
is not quite enough to
counteract the amount of water

246
00:10:36,452 --> 00:10:37,410
that's already in here.

247
00:10:37,410 --> 00:10:43,190
But if we add enough eventually
it will turn totally red.

248
00:10:43,190 --> 00:10:48,452
But for it now you can see it's
an equilibrium reaction, yay.

249
00:10:52,500 --> 00:10:55,060
CATHERINE DRENNAN: And it talks
about also rates of reactions

250
00:10:55,060 --> 00:10:58,000
and rates of exchange,
and that's our next unit.

251
00:10:58,000 --> 00:11:01,500
[LAUGHTER]

252
00:11:02,970 --> 00:11:05,958
GUEST SPEAKER: Yay.

253
00:11:05,958 --> 00:11:06,954
[CLASS OOHS]

254
00:11:06,954 --> 00:11:08,335
GUEST SPEAKER: Aw.

255
00:11:08,335 --> 00:11:10,501
Well, that's a good lead
in to the next demo, right?

256
00:11:13,852 --> 00:11:15,060
CATHERINE DRENNAN: All right.

257
00:11:15,060 --> 00:11:15,896
Thank you guys.

258
00:11:20,750 --> 00:11:22,680
So you saw that
red color develop,

259
00:11:22,680 --> 00:11:24,740
and so it's not just
about whether something is

260
00:11:24,740 --> 00:11:26,240
a strong or weak field ligand.

261
00:11:26,240 --> 00:11:28,080
It's also about the geometry.

262
00:11:28,080 --> 00:11:30,610
So we're going to talk later
about square planar geometry,

263
00:11:30,610 --> 00:11:32,510
so keep in mind that
we'd expect that there

264
00:11:32,510 --> 00:11:35,390
should be some splitting
between those d orbitals.

265
00:11:35,390 --> 00:11:38,351
But before we get
to square planar

266
00:11:38,351 --> 00:11:39,600
we're going to do tetrahedral.

267
00:11:42,690 --> 00:11:44,850
So here is our
tetrahedral system.

268
00:11:44,850 --> 00:11:47,240
Here's my little
drawing of tetrahedral,

269
00:11:47,240 --> 00:11:50,360
and I have my
tetrahedral model here.

270
00:11:50,360 --> 00:11:54,710
And so here we're going to
have our tetrahedral coordinate

271
00:11:54,710 --> 00:11:57,080
frame like this, where
we have two ligands

272
00:11:57,080 --> 00:11:58,830
in the plane of the screen.

273
00:11:58,830 --> 00:12:01,970
One ligand coming out at you
and one ligand going back.

274
00:12:01,970 --> 00:12:04,520
And so now we're going
to think about how

275
00:12:04,520 --> 00:12:08,750
our different sets of d orbitals
are going to be affected

276
00:12:08,750 --> 00:12:11,420
by tetrahedral geometry.

277
00:12:11,420 --> 00:12:14,060
And again, remember crystal
field theory is just

278
00:12:14,060 --> 00:12:17,480
saying that the ligands are
like negative charges pointing

279
00:12:17,480 --> 00:12:19,170
toward the d orbitals.

280
00:12:19,170 --> 00:12:21,740
So when the ligand
and the d orbital

281
00:12:21,740 --> 00:12:23,510
are near each other--
big repulsion.

282
00:12:23,510 --> 00:12:26,780
When they're farther
away-- less repulsion.

283
00:12:26,780 --> 00:12:29,690
So let's look at this case now.

284
00:12:29,690 --> 00:12:33,720
And so here we see
in this geometry

285
00:12:33,720 --> 00:12:36,470
our ligands are now off axis.

286
00:12:36,470 --> 00:12:37,980
Here is the z-axis.

287
00:12:37,980 --> 00:12:39,100
Here's the y-axis.

288
00:12:39,100 --> 00:12:40,340
Here is the x-axis.

289
00:12:40,340 --> 00:12:42,230
Our ligands are off axis.

290
00:12:42,230 --> 00:12:46,100
So our orbital sets that
are also kind of off axis

291
00:12:46,100 --> 00:12:49,580
are going to be more affected
than our orbital sets that

292
00:12:49,580 --> 00:12:51,260
were on axis.

293
00:12:51,260 --> 00:12:53,360
So this is different
from what we saw

294
00:12:53,360 --> 00:12:55,290
with the octahedral geometry.

295
00:12:55,290 --> 00:12:58,430
So now we have more repulsion
between those negative point

296
00:12:58,430 --> 00:13:02,300
charges that are the ligands
and the d orbitals that

297
00:13:02,300 --> 00:13:03,080
are off axis.

298
00:13:03,080 --> 00:13:05,340
The ones that are
45 degrees away.

299
00:13:05,340 --> 00:13:11,420
So our dyz, dzy, and dxz.

300
00:13:11,420 --> 00:13:15,170
So this is, in
fact, the opposite

301
00:13:15,170 --> 00:13:18,950
of the octahedral case
because in the octahedral case

302
00:13:18,950 --> 00:13:21,530
we had-- the
ligands were on axis

303
00:13:21,530 --> 00:13:24,470
and so the orbitals that were
on axes were the most affected.

304
00:13:24,470 --> 00:13:27,320
But now with tetrahedral
ligand's off axis so

305
00:13:27,320 --> 00:13:30,270
the orbitals that are off
axis are the most effective.

306
00:13:30,270 --> 00:13:35,090
So these switch positions now.

307
00:13:35,090 --> 00:13:40,730
And dx squared minus
y squared dz squared.

308
00:13:40,730 --> 00:13:42,540
They still have the same energy.

309
00:13:42,540 --> 00:13:45,020
They're still degenerate
with respect to each other,

310
00:13:45,020 --> 00:13:48,500
but now these are stabilized
compared to these.

311
00:13:48,500 --> 00:13:50,450
But they also have
the same energy.

312
00:13:50,450 --> 00:13:52,700
So all of these
three orbital sets

313
00:13:52,700 --> 00:13:54,140
are also at the same energy.

314
00:13:54,140 --> 00:13:56,840
Also degenerate.

315
00:13:56,840 --> 00:13:59,390
Now, one other really important
thing about tetrahedral

316
00:13:59,390 --> 00:14:03,200
is not only is it the opposite
of octahedral in terms

317
00:14:03,200 --> 00:14:07,010
of where those orbitals
are, but overall they're

318
00:14:07,010 --> 00:14:08,720
sort of less splitting.

319
00:14:08,720 --> 00:14:13,790
So even though the orbitals
that are kind of off axis

320
00:14:13,790 --> 00:14:16,670
are more affected by
that tetrahedral geometry

321
00:14:16,670 --> 00:14:19,490
than the others,
still the ligands

322
00:14:19,490 --> 00:14:22,310
aren't really pointing right
toward those orbitals at all.

323
00:14:22,310 --> 00:14:24,200
They're closer but
they're not right at them.

324
00:14:24,200 --> 00:14:27,560
So it's very different
from the octahedral case

325
00:14:27,560 --> 00:14:32,000
where you had the orbitals
sort of right on axis

326
00:14:32,000 --> 00:14:33,650
and the ligands right on axis.

327
00:14:33,650 --> 00:14:35,270
So there's less splitting.

328
00:14:35,270 --> 00:14:37,130
It's smaller splitting.

329
00:14:37,130 --> 00:14:40,610
So the octahedral, or the
tetrahedral crystal field

330
00:14:40,610 --> 00:14:43,640
splitting energy,
is this delta sub t.

331
00:14:43,640 --> 00:14:45,950
And that's going to be smaller.

332
00:14:45,950 --> 00:14:48,440
So let's look now at some
crystal field splitting

333
00:14:48,440 --> 00:14:49,940
diagrams.

334
00:14:49,940 --> 00:14:52,880
I'm going to compare
the octahedral case

335
00:14:52,880 --> 00:14:54,770
with the tetrahedral case.

336
00:14:54,770 --> 00:14:57,590
So here is our
octahedral case again.

337
00:14:57,590 --> 00:15:00,620
We have our octahedral crystal
field splitting energy--

338
00:15:00,620 --> 00:15:04,160
our delta O. Now we have our
tetrahedral crystal field

339
00:15:04,160 --> 00:15:07,010
splitting energy-- delta t.

340
00:15:07,010 --> 00:15:11,510
And we see again that
it's opposite orders.

341
00:15:11,510 --> 00:15:14,640
So our dx squared
minus y squared

342
00:15:14,640 --> 00:15:18,260
dz squared, instead of being up
here as it is with octahedral,

343
00:15:18,260 --> 00:15:20,030
is now down here.

344
00:15:20,030 --> 00:15:23,870
And instead of our EG
we now just have E.

345
00:15:23,870 --> 00:15:26,360
We just lost the G here.

346
00:15:26,360 --> 00:15:30,620
And our three sets that
were stabilized, compared

347
00:15:30,620 --> 00:15:33,640
to the hypothetical
spherical crystal field,

348
00:15:33,640 --> 00:15:38,030
are now de-stabilized because
those orbitals at 45 degrees

349
00:15:38,030 --> 00:15:40,880
are closer to our
tetrahedral ligands.

350
00:15:40,880 --> 00:15:43,530
So again, we have this switch.

351
00:15:43,530 --> 00:15:49,532
And again, our EG goes to just
G. The book sometimes has E2.

352
00:15:49,532 --> 00:15:51,740
I don't know where that came
from but you should just

353
00:15:51,740 --> 00:15:52,239
ignore it.

354
00:15:52,239 --> 00:15:58,040
It's just E. And T2G
is now is just T2.

355
00:15:58,040 --> 00:16:00,830
So again, you can
see in this picture

356
00:16:00,830 --> 00:16:04,400
really well-- splitting energy
is a lot less for tetrahedral.

357
00:16:04,400 --> 00:16:07,880
This is much smaller than
the octahedral crystal field

358
00:16:07,880 --> 00:16:11,054
splitting energy, so much,
much smaller because again,

359
00:16:11,054 --> 00:16:12,470
none of those
ligand point charges

360
00:16:12,470 --> 00:16:14,540
are really directly
toward those orbitals.

361
00:16:14,540 --> 00:16:17,270
So overall, it's less splitting.

362
00:16:17,270 --> 00:16:20,420
And because there's
less splitting, when

363
00:16:20,420 --> 00:16:24,620
you think about putting
electrons in to the system

364
00:16:24,620 --> 00:16:27,350
it doesn't take
much to go up here.

365
00:16:27,350 --> 00:16:29,390
So the pairing energies
is going to always

366
00:16:29,390 --> 00:16:33,920
be a lot greater than the energy
to put it in this higher energy

367
00:16:33,920 --> 00:16:35,810
orbital set because
it's not very much

368
00:16:35,810 --> 00:16:37,520
higher than the first set.

369
00:16:37,520 --> 00:16:40,340
So these would all
be high spin systems.

370
00:16:40,340 --> 00:16:42,440
So we put in our
electrons singly

371
00:16:42,440 --> 00:16:47,750
to the fullest extent possible
before we start to pair them.

372
00:16:47,750 --> 00:16:50,660
So you can assume that
all tetrahedral complexes

373
00:16:50,660 --> 00:16:51,650
are high spins.

374
00:16:51,650 --> 00:16:54,650
That's a pretty good assumption.

375
00:16:54,650 --> 00:16:57,710
So just like the
tetrahedral case,

376
00:16:57,710 --> 00:16:59,630
we have overall--
we're maintaining

377
00:16:59,630 --> 00:17:01,770
the energy of the system.

378
00:17:01,770 --> 00:17:04,910
So in the tetrahedral
case we had three orbitals

379
00:17:04,910 --> 00:17:06,849
that were stabilized.

380
00:17:06,849 --> 00:17:11,780
So they went down by
2/5 and two that went up

381
00:17:11,780 --> 00:17:14,030
were de-stabilized,
so they went up

382
00:17:14,030 --> 00:17:17,690
by 3/5 to maintain the
overall energy of the system.

383
00:17:17,690 --> 00:17:21,470
In the tetrahedral case
we have two orbitals

384
00:17:21,470 --> 00:17:23,359
that are stabilized
down in energy,

385
00:17:23,359 --> 00:17:26,270
so they're down by minus 3/5.

386
00:17:26,270 --> 00:17:29,600
And then we have three up,
so those are up by 2/5.

387
00:17:29,600 --> 00:17:34,790
So same idea, but again,
everything is opposite.

388
00:17:34,790 --> 00:17:36,950
So let's take a
look at an example

389
00:17:36,950 --> 00:17:43,850
of the tetrahedral case, and
we'll look at chromium 3 plus.

390
00:17:43,850 --> 00:17:47,960
So what is the d count here?

391
00:17:47,960 --> 00:17:49,850
Who can just tell me?

392
00:17:49,850 --> 00:17:51,285
Find chromium in our table.

393
00:17:54,390 --> 00:17:54,890
Yup.

394
00:17:54,890 --> 00:17:59,680
It's going to be three,
so group 6 minus 3 is 3.

395
00:17:59,680 --> 00:18:02,000
And now, why don't
you tell me how

396
00:18:02,000 --> 00:18:06,010
we are going to put in
those three electrons?

397
00:18:15,781 --> 00:18:16,280
All right.

398
00:18:16,280 --> 00:18:17,170
10 more seconds.

399
00:18:31,440 --> 00:18:32,110
OK.

400
00:18:32,110 --> 00:18:33,800
Most people got that right.

401
00:18:33,800 --> 00:18:37,820
So again, this is not correct
for a high spin, which

402
00:18:37,820 --> 00:18:40,190
most tetrahedral compounds are.

403
00:18:40,190 --> 00:18:41,490
This would be correct.

404
00:18:41,490 --> 00:18:43,910
This arrangement of
electrons is also correct,

405
00:18:43,910 --> 00:18:48,200
but if you look at the orbital
names those are incorrect.

406
00:18:48,200 --> 00:18:52,340
So on a test you need
to be able to write

407
00:18:52,340 --> 00:18:55,670
all the correct orbital names
and the correct designators

408
00:18:55,670 --> 00:18:58,580
as well, as well as
putting it in the electrons

409
00:18:58,580 --> 00:18:59,570
in the right way.

410
00:18:59,570 --> 00:19:01,670
So good to practice.

411
00:19:01,670 --> 00:19:06,840
So we put in now our
three electrons over here,

412
00:19:06,840 --> 00:19:11,520
and now we can think about
our dn configuration.

413
00:19:11,520 --> 00:19:13,970
So if you're asked to
write out the d to the n

414
00:19:13,970 --> 00:19:17,930
electron configuration,
what that's asking you for

415
00:19:17,930 --> 00:19:21,830
is to say how many electrons
are in which of the two

416
00:19:21,830 --> 00:19:23,180
orbital levels.

417
00:19:23,180 --> 00:19:27,890
And so you would say, in the
e level here you have two

418
00:19:27,890 --> 00:19:31,100
and in the t2
level you have one.

419
00:19:31,100 --> 00:19:32,720
And this is just
then a shorthand.

420
00:19:32,720 --> 00:19:35,030
That's why they have these
little abbreviations.

421
00:19:35,030 --> 00:19:40,190
You don't have to write out all
the names of your d orbitals.

422
00:19:40,190 --> 00:19:44,870
So how many unpaired
electrons do we have then?

423
00:19:44,870 --> 00:19:46,720
We have what?

424
00:19:46,720 --> 00:19:48,140
Three.

425
00:19:48,140 --> 00:19:55,370
And if I'm now telling you that
this is a complex with chloride

426
00:19:55,370 --> 00:19:58,520
and that the wavelength of the
most intensely absorbed light

427
00:19:58,520 --> 00:20:01,730
is 740, why don't
you predict the color

428
00:20:01,730 --> 00:20:03,040
of the complex for me?

429
00:20:12,451 --> 00:20:12,950
OK.

430
00:20:12,950 --> 00:20:13,775
10 more seconds.

431
00:20:27,120 --> 00:20:29,440
Yup.

432
00:20:29,440 --> 00:20:32,830
So we can look and
see this wavelength

433
00:20:32,830 --> 00:20:36,010
is going to be in the red
so that the predictive color

434
00:20:36,010 --> 00:20:40,870
of the complex would be the
complimentary, or green.

435
00:20:40,870 --> 00:20:48,320
And so green then is one
that has-- it's pretty short.

436
00:20:48,320 --> 00:20:49,960
This is a pretty
long wavelength,

437
00:20:49,960 --> 00:20:53,237
which would be consistent with
a very tiny splitting energy.

438
00:20:57,190 --> 00:20:59,770
So now let's think about
the square planar case.

439
00:21:02,720 --> 00:21:07,850
So our square planar
system is described--

440
00:21:07,850 --> 00:21:10,240
so we're in the plane here.

441
00:21:10,240 --> 00:21:12,290
It's, again, square planar.

442
00:21:12,290 --> 00:21:17,180
And now we have our
ligands along the y-axis

443
00:21:17,180 --> 00:21:18,870
and the x-axis.

444
00:21:18,870 --> 00:21:22,710
So we have nothing
along the z-axis here.

445
00:21:22,710 --> 00:21:26,540
So tell me, based on this
and then again our ligands

446
00:21:26,540 --> 00:21:30,950
are on axis, which
of those d orbitals

447
00:21:30,950 --> 00:21:33,050
do you think is
going to be the most

448
00:21:33,050 --> 00:21:35,630
de-stabilized by this geometry?

449
00:21:35,630 --> 00:21:38,050
What do you think?

450
00:21:38,050 --> 00:21:39,504
You can just yell it out.

451
00:21:39,504 --> 00:21:41,395
AUDIENCE: x squared
minus y squared.

452
00:21:41,395 --> 00:21:43,770
CATHERINE DRENNAN: x
squared minus y squared.

453
00:21:43,770 --> 00:21:46,320
And what would you think
would be next in terms

454
00:21:46,320 --> 00:21:50,690
of de-stabilized of those sets?

455
00:21:50,690 --> 00:21:51,740
xy?

456
00:21:51,740 --> 00:21:54,150
Yeah, so that's the case.

457
00:21:54,150 --> 00:21:57,350
So most is going to be dx
squared minus y squared.

458
00:21:57,350 --> 00:21:59,420
Again, those
orbitals are on axes.

459
00:21:59,420 --> 00:22:00,770
ligands on axis.

460
00:22:00,770 --> 00:22:04,190
Next would be the other
one that has x and y.

461
00:22:04,190 --> 00:22:06,380
So let's take a
look at this now.

462
00:22:06,380 --> 00:22:10,970
So we have our dx
squared minus y squared.

463
00:22:10,970 --> 00:22:12,470
Our orbitals are on axis.

464
00:22:12,470 --> 00:22:13,760
Our ligands are on axis.

465
00:22:13,760 --> 00:22:16,320
You really have
lots of repulsion.

466
00:22:16,320 --> 00:22:19,320
So this would be de-stabilized
the most compared

467
00:22:19,320 --> 00:22:21,290
to all other d orbitals.

468
00:22:21,290 --> 00:22:24,260
Really different amount
of destabilization.

469
00:22:24,260 --> 00:22:26,420
This is a lot of repulsion.

470
00:22:26,420 --> 00:22:29,660
All the ligands are right
toward those orbitals.

471
00:22:29,660 --> 00:22:33,740
So dz squared, which
used to be degenerate

472
00:22:33,740 --> 00:22:37,680
with dx squared minus y
squared now is not anymore.

473
00:22:37,680 --> 00:22:39,840
There's a lot less
repulsion for this

474
00:22:39,840 --> 00:22:45,020
because there's no ligands
along the z-axis anymore.

475
00:22:45,020 --> 00:22:47,180
So let's look at our
other orbital set.

476
00:22:47,180 --> 00:22:51,950
The next one in terms of
being de-stabilized is dxy.

477
00:22:51,950 --> 00:22:55,670
Now, these orbitals are off axis
so it's not nearly as bad as

478
00:22:55,670 --> 00:22:58,340
for dx squared minus y squared.

479
00:22:58,340 --> 00:23:01,290
But compared to
everything else it's

480
00:23:01,290 --> 00:23:03,890
a lot more repulsion
than everybody else,

481
00:23:03,890 --> 00:23:08,780
but it's less than our dx
squared minus y squared.

482
00:23:08,780 --> 00:23:10,940
And these guys are then
going to be stabilized

483
00:23:10,940 --> 00:23:13,010
compared to the others.

484
00:23:13,010 --> 00:23:16,010
So let's now draw our
splitting diagrams

485
00:23:16,010 --> 00:23:19,460
and think about how this
all plays in together.

486
00:23:19,460 --> 00:23:22,640
And so again, we'll compare
it to our octahedral crystal

487
00:23:22,640 --> 00:23:24,080
field.

488
00:23:24,080 --> 00:23:29,750
So now, the most de-stabilized
way up here, which

489
00:23:29,750 --> 00:23:33,460
is this orbital going to be?

490
00:23:33,460 --> 00:23:34,720
Which one?

491
00:23:34,720 --> 00:23:36,271
x squared minus y squared.

492
00:23:36,271 --> 00:23:36,770
Right.

493
00:23:36,770 --> 00:23:40,130
That's up in energy the
most, so most de-stabilized.

494
00:23:40,130 --> 00:23:43,640
It's experiencing
the most repulsion.

495
00:23:43,640 --> 00:23:49,190
And then next, but
much lower down, dxy.

496
00:23:49,190 --> 00:23:52,740
Again, the ligands are
along in the xy plane,

497
00:23:52,740 --> 00:23:53,820
so that would be second.

498
00:23:53,820 --> 00:23:58,280
But those are 45 degrees off
axis so it's way down in energy

499
00:23:58,280 --> 00:24:00,890
compared to the ones
that are on axis.

500
00:24:00,890 --> 00:24:03,840
And then down here we
kind of have all the rest,

501
00:24:03,840 --> 00:24:08,090
and it's usually written
with dz squared here

502
00:24:08,090 --> 00:24:14,050
and then dyz and dxz over here.

503
00:24:14,050 --> 00:24:16,580
But the order here--
these are all kind of

504
00:24:16,580 --> 00:24:20,010
stabilized compared to these
two and the exact order

505
00:24:20,010 --> 00:24:24,800
is not quite as firm as in
octahedral or tetrahedral

506
00:24:24,800 --> 00:24:25,850
cases.

507
00:24:25,850 --> 00:24:28,430
So again, this is
quite different now.

508
00:24:28,430 --> 00:24:32,340
Overall, the energy
is also maintained,

509
00:24:32,340 --> 00:24:34,485
but there's too many
orbitals in too many places

510
00:24:34,485 --> 00:24:36,840
so you're not
expected to know that.

511
00:24:36,840 --> 00:24:38,960
But one thing that
I will point out

512
00:24:38,960 --> 00:24:41,850
is that remember for
the demo square planar--

513
00:24:41,850 --> 00:24:44,390
we said that had to have
a pretty big splitting?

514
00:24:44,390 --> 00:24:47,660
That's a really big splitting
of the energy of the orbital.

515
00:24:47,660 --> 00:24:50,030
So square planar
complexes can be

516
00:24:50,030 --> 00:24:53,570
capable of having
big energies-- you

517
00:24:53,570 --> 00:24:55,880
need a big energy
of your photon to be

518
00:24:55,880 --> 00:24:57,179
absorbed by a square planar.

519
00:24:57,179 --> 00:24:59,720
Or you could if you're going to
bump it all the way up there.

520
00:24:59,720 --> 00:25:02,780
That's really far away.

521
00:25:02,780 --> 00:25:06,840
So now, clicker.

522
00:25:06,840 --> 00:25:09,440
Why don't you tell
me what you think

523
00:25:09,440 --> 00:25:12,530
of a square pyramidal case?

524
00:25:12,530 --> 00:25:17,690
And this would be this case
here where you have one ligand.

525
00:25:17,690 --> 00:25:20,130
You have a square planar
geometry, basically,

526
00:25:20,130 --> 00:25:22,620
that you've added
an extra ligand too.

527
00:25:22,620 --> 00:25:24,760
Or you had octahedral
you took one away,

528
00:25:24,760 --> 00:25:27,021
and that extra ligand
is along the z-axis.

529
00:25:27,021 --> 00:25:28,770
So what things do you
think would be true?

530
00:25:39,729 --> 00:25:41,270
Since we're running
out of time let's

531
00:25:41,270 --> 00:25:42,610
just take 10 more seconds.

532
00:26:00,320 --> 00:26:04,940
So just to put--
that would be true.

533
00:26:04,940 --> 00:26:08,330
Now there's a ligand
along z, so dz squared

534
00:26:08,330 --> 00:26:11,570
is going to be de-stabilized
in the square pyramidal case

535
00:26:11,570 --> 00:26:13,910
compared to the square planar.

536
00:26:13,910 --> 00:26:18,410
Everything that has z's in it
would also be de-stabilized,

537
00:26:18,410 --> 00:26:21,250
and these would definitely
not be degenerate.

538
00:26:21,250 --> 00:26:24,560
There's no reason they would
have the same energy there.

539
00:26:24,560 --> 00:26:26,850
So we'll get to our
bio example on Monday,

540
00:26:26,850 --> 00:26:30,530
but first what are the results?

541
00:26:30,530 --> 00:26:34,030
[CHEERING]

542
00:26:40,745 --> 00:26:41,245
Awesome.

543
00:26:46,400 --> 00:26:47,650
Congratulations.

544
00:26:47,650 --> 00:26:50,042
That was unexpected.

545
00:26:50,042 --> 00:26:53,190
Two new groups.

546
00:26:53,190 --> 00:26:53,690
All right.

547
00:26:53,690 --> 00:26:54,780
Have a good weekend.

548
00:26:54,780 --> 00:26:56,900
See you Monday.

549
00:26:56,900 --> 00:27:03,460
So end of lecture 29 last page.

550
00:27:03,460 --> 00:27:05,600
We were talking about
biological examples.

551
00:27:05,600 --> 00:27:07,280
We were talking about
transition metals.

552
00:27:07,280 --> 00:27:10,220
We're talking about
colors of things.

553
00:27:10,220 --> 00:27:14,030
And I just wanted to give
you an example of why

554
00:27:14,030 --> 00:27:16,490
geometry can matter
or be interesting

555
00:27:16,490 --> 00:27:18,920
from a biological context.

556
00:27:18,920 --> 00:27:22,850
So the video that you
heard about nickel

557
00:27:22,850 --> 00:27:26,090
showed that nickel
allows H.pylori

558
00:27:26,090 --> 00:27:31,100
to colonize your stomach because
the nickel enzyme creates

559
00:27:31,100 --> 00:27:33,860
a buffering system so
that it can survive

560
00:27:33,860 --> 00:27:35,710
in the low pH of your stomach.

561
00:27:35,710 --> 00:27:38,870
And it's very hard to
treat H.pylori infections

562
00:27:38,870 --> 00:27:41,330
because the antibiotics
that you would

563
00:27:41,330 --> 00:27:44,690
give to kill the
bacteria get destroyed

564
00:27:44,690 --> 00:27:48,320
in acidity of the stomach,
so it's a very hard problem.

565
00:27:48,320 --> 00:27:51,290
And it's fascinating that they
can use this nickel enzyme

566
00:27:51,290 --> 00:27:54,150
to kind of allow themselves
to live in this environment,

567
00:27:54,150 --> 00:27:55,280
so that's pretty cool.

568
00:27:55,280 --> 00:27:58,040
This is also really
cool and arguably more

569
00:27:58,040 --> 00:27:59,810
beneficial to mankind.

570
00:27:59,810 --> 00:28:02,330
So nickel dependent
enzymes also are

571
00:28:02,330 --> 00:28:05,570
responsible for removing a lot
of carbon monoxide and carbon

572
00:28:05,570 --> 00:28:07,580
dioxide from the environment.

573
00:28:07,580 --> 00:28:11,330
So microbes have
these enzymes that

574
00:28:11,330 --> 00:28:13,670
allow them to use carbon
monoxide and carbon

575
00:28:13,670 --> 00:28:17,780
dioxide as their carbon
source for metabolism.

576
00:28:17,780 --> 00:28:20,900
And so collectively,
these microbes

577
00:28:20,900 --> 00:28:23,780
are estimated to remove about
100 million tons of carbon

578
00:28:23,780 --> 00:28:26,000
monoxide from the
environment every year

579
00:28:26,000 --> 00:28:29,150
and produce about 1 trillion
kilograms of acetate

580
00:28:29,150 --> 00:28:32,090
from greenhouse and
other gases, such as CO2.

581
00:28:32,090 --> 00:28:36,579
So there's a lot of benefit to
us from these nickel enzymes.

582
00:28:36,579 --> 00:28:38,120
And so people are
interested in doing

583
00:28:38,120 --> 00:28:39,309
a couple different things.

584
00:28:39,309 --> 00:28:40,850
One thing they're
interested in doing

585
00:28:40,850 --> 00:28:42,740
is to see what
these nickel centers

586
00:28:42,740 --> 00:28:45,830
look like so that they can
make small molecules to do

587
00:28:45,830 --> 00:28:47,210
the same chemistry.

588
00:28:47,210 --> 00:28:51,950
People are also interested in
taking these microbes as such

589
00:28:51,950 --> 00:28:55,190
and getting them to
overexpress these enzymes

590
00:28:55,190 --> 00:28:59,060
and then convert things
like CO2, greenhouse gas,

591
00:28:59,060 --> 00:29:00,420
into biofuels.

592
00:29:00,420 --> 00:29:02,240
So some people in
chemical engineering

593
00:29:02,240 --> 00:29:06,290
are doing that right now, and
I'm collaborating with them

594
00:29:06,290 --> 00:29:07,860
on some of these projects.

595
00:29:07,860 --> 00:29:10,940
So this is, again, a very--
everyone is very concerned

596
00:29:10,940 --> 00:29:15,532
about climate and so this
is a hot area of research.

597
00:29:15,532 --> 00:29:17,990
So of course, if you want to
know what something looks like

598
00:29:17,990 --> 00:29:20,180
at atomic level,
x-ray crystallography

599
00:29:20,180 --> 00:29:21,720
is a great thing to do.

600
00:29:21,720 --> 00:29:24,510
But if you don't have
a crystal structure

601
00:29:24,510 --> 00:29:26,660
you can use spectroscopy.

602
00:29:26,660 --> 00:29:28,190
In particular, you
can think about

603
00:29:28,190 --> 00:29:31,640
whether the enzyme
and this nickel center

604
00:29:31,640 --> 00:29:34,520
is paramagnetic or
diamagnetic, and that

605
00:29:34,520 --> 00:29:37,680
can help you guess what the
geometry of the metal center

606
00:29:37,680 --> 00:29:38,180
is.

607
00:29:38,180 --> 00:29:39,920
So this is sort of
a first experiment

608
00:29:39,920 --> 00:29:41,750
you might try to
do to understand

609
00:29:41,750 --> 00:29:44,870
what's going on in your enzyme.

610
00:29:44,870 --> 00:29:48,410
So say you have a nickel
plus 2 or d8 center

611
00:29:48,410 --> 00:29:50,930
and it's found to
be diamagnetic.

612
00:29:50,930 --> 00:29:54,380
Then we could be asked,
can you rule in or out

613
00:29:54,380 --> 00:29:56,750
some of the common
geometries for nickel

614
00:29:56,750 --> 00:29:59,640
based on this
single observation?

615
00:29:59,640 --> 00:30:01,880
So let's do that.

616
00:30:01,880 --> 00:30:04,410
So we want to add
some electrons.

617
00:30:04,410 --> 00:30:07,700
So I'm going to go over
here, and I have our diagrams

618
00:30:07,700 --> 00:30:08,900
on the board.

619
00:30:08,900 --> 00:30:12,320
So first, octahedral
is a common geometry.

620
00:30:12,320 --> 00:30:17,690
Does it matter if this has a
big splitting or small splitting

621
00:30:17,690 --> 00:30:20,160
for a d8 center?

622
00:30:20,160 --> 00:30:21,670
What do you think?

623
00:30:21,670 --> 00:30:25,100
Think about it for a minute.

624
00:30:25,100 --> 00:30:26,840
Let's try it and see.

625
00:30:26,840 --> 00:30:30,620
So if we have a
small splitting we

626
00:30:30,620 --> 00:30:33,320
would go-- we put in
our three electrons.

627
00:30:33,320 --> 00:30:36,600
And again, this is a d8 system,
so we have eight electrons.

628
00:30:36,600 --> 00:30:38,300
We put in our three
and now we have

629
00:30:38,300 --> 00:30:40,790
to decide if we're
going to go up here

630
00:30:40,790 --> 00:30:42,440
or if we're going to pair.

631
00:30:42,440 --> 00:30:46,180
But let's pretend it's
a small splitting,

632
00:30:46,180 --> 00:30:48,700
so we'll put an
electron up here.

633
00:30:48,700 --> 00:30:49,820
Than we're done.

634
00:30:49,820 --> 00:30:52,601
Now we have to pair, so we're
going to come back down here

635
00:30:52,601 --> 00:30:55,100
to pair because we're going to
put them in the lowest energy

636
00:30:55,100 --> 00:30:56,030
orbitals.

637
00:30:56,030 --> 00:30:59,970
So we have five, six, seven,
eight, and we're done.

638
00:30:59,970 --> 00:31:02,510
Now, if we said that
the splitting was big

639
00:31:02,510 --> 00:31:05,810
we would have paired all
of these electrons first

640
00:31:05,810 --> 00:31:09,819
and then put two electrons
singly at the upper level.

641
00:31:09,819 --> 00:31:11,360
And that would have
given us actually

642
00:31:11,360 --> 00:31:13,890
the exact same diagram.

643
00:31:13,890 --> 00:31:15,530
So in this particular
case, it doesn't

644
00:31:15,530 --> 00:31:19,460
matter whether there's a big
splitting or a small splitting.

645
00:31:19,460 --> 00:31:22,790
You get the same
electron configuration.

646
00:31:22,790 --> 00:31:27,077
So is this diamagnetic
or paramagnetic?

647
00:31:27,077 --> 00:31:28,035
AUDIENCE: Paramagnetic.

648
00:31:28,035 --> 00:31:29,540
CATHERINE DRENNAN: Paramagnetic.

649
00:31:29,540 --> 00:31:30,620
Which means what?

650
00:31:35,520 --> 00:31:39,050
It means that you have
unpaired electrons.

651
00:31:39,050 --> 00:31:42,910
So we have unpaired electrons
so it's paramagnetic.

652
00:31:42,910 --> 00:31:47,410
So let's look at the
square planar system now.

653
00:31:47,410 --> 00:31:51,910
So we have three orbitals
that are down in energy,

654
00:31:51,910 --> 00:31:57,130
and because our square planar
system is in the xy plane

655
00:31:57,130 --> 00:31:59,740
and it's on axis and we
have-- so our ligand's

656
00:31:59,740 --> 00:32:04,690
on axis and our
ligands on axis point

657
00:32:04,690 --> 00:32:06,490
toward the orbitals on axis.

658
00:32:06,490 --> 00:32:10,750
So dx squared minus y squared
is really high in energy.

659
00:32:10,750 --> 00:32:13,180
xy is a little bit
higher, and these guys

660
00:32:13,180 --> 00:32:14,620
are down at the bottom.

661
00:32:14,620 --> 00:32:16,816
So we don't really know
anything about where

662
00:32:16,816 --> 00:32:18,940
we're going to put them
in, but let's just put them

663
00:32:18,940 --> 00:32:20,600
in singly in these lower ones.

664
00:32:20,600 --> 00:32:26,160
So we'll do one, two, three,
and then we'll pair them up.

665
00:32:26,160 --> 00:32:28,136
Four, five, six.

666
00:32:28,136 --> 00:32:32,870
And then we have two more,
so that's seven, eight.

667
00:32:32,870 --> 00:32:35,860
And we definitely, unless
we absolutely have to,

668
00:32:35,860 --> 00:32:38,860
don't want to put any
electrons in our dx squared

669
00:32:38,860 --> 00:32:39,822
minus y squared.

670
00:32:39,822 --> 00:32:41,530
That's way up in
energy, so we don't want

671
00:32:41,530 --> 00:32:43,930
to do that unless we have to.

672
00:32:43,930 --> 00:32:46,990
So is this paramagnetic
or diamagnetic?

673
00:32:46,990 --> 00:32:47,910
AUDIENCE: Diamagnetic.

674
00:32:47,910 --> 00:32:49,201
CATHERINE DRENNAN: Diamagnetic.

675
00:32:49,201 --> 00:32:52,030
So we have one
option here that is

676
00:32:52,030 --> 00:32:56,620
consistent with
the spectroscopy.

677
00:32:56,620 --> 00:32:58,960
Now let's look at tetrahedral.

678
00:32:58,960 --> 00:33:01,300
Is tetrahedral--
what do you think?

679
00:33:01,300 --> 00:33:03,160
Is it going to be
high spin or low spin?

680
00:33:05,740 --> 00:33:08,380
High spin so we'll
have a small splitting,

681
00:33:08,380 --> 00:33:12,100
and that is because in
the tetrahedral geometry

682
00:33:12,100 --> 00:33:15,250
you have-- your
ligands are off axis,

683
00:33:15,250 --> 00:33:18,580
so we have an opposite
of the octahedral system.

684
00:33:18,580 --> 00:33:21,730
The orbitals that were higher
in energy, more destabilized,

685
00:33:21,730 --> 00:33:22,930
are now lower.

686
00:33:22,930 --> 00:33:25,480
But the ligands aren't
really pointing directly

687
00:33:25,480 --> 00:33:29,080
toward any of the d orbitals,
so the splitting overall

688
00:33:29,080 --> 00:33:30,530
is much smaller.

689
00:33:30,530 --> 00:33:34,000
So this splitting is always
going to be pretty small,

690
00:33:34,000 --> 00:33:36,190
and so that leads to
a high spin system,

691
00:33:36,190 --> 00:33:39,560
which is you have the maximum
number of unpaired electrons.

692
00:33:39,560 --> 00:33:43,030
So you can always assume
it's high spin or splitting

693
00:33:43,030 --> 00:33:45,220
is small, so we're going
to put your electrons

694
00:33:45,220 --> 00:33:48,790
in singly to the fullest extent
possible before you pair.

695
00:33:48,790 --> 00:33:57,550
So we'll put one, two, three,
four, five, six, seven, eight.

696
00:33:57,550 --> 00:34:00,070
So is this diamagnetic
or paramagnetic?

697
00:34:00,070 --> 00:34:01,120
AUDIENCE: Paramagnetic.

698
00:34:01,120 --> 00:34:02,453
CATHERINE DRENNAN: Paramagnetic.

699
00:34:07,500 --> 00:34:11,310
So of these three
choices, the only one

700
00:34:11,310 --> 00:34:14,489
that would be consistent
with the spectroscopy

701
00:34:14,489 --> 00:34:18,600
is the square planar system, and
that turned out to be correct.

702
00:34:18,600 --> 00:34:22,420
It was a square planar system.

703
00:34:22,420 --> 00:34:26,739
And so here is a picture of
that square planar system.

704
00:34:26,739 --> 00:34:28,980
So here we have the
nickel in the middle

705
00:34:28,980 --> 00:34:33,210
and we have four ligands
all in one plane.

706
00:34:33,210 --> 00:34:36,840
So we have this really
nice square planar geometry

707
00:34:36,840 --> 00:34:39,870
that people predicted
would exist before there

708
00:34:39,870 --> 00:34:41,500
was a crystal structure.

709
00:34:41,500 --> 00:34:45,030
And so this is one of the
catalysts for allowing microbes

710
00:34:45,030 --> 00:34:49,080
to live on carbon dioxide as
their carbon source, which

711
00:34:49,080 --> 00:34:53,850
is really an incredible thing
that an organism can do.

712
00:34:53,850 --> 00:34:56,650
Little microbes,
bacteria-- super cool.

713
00:34:56,650 --> 00:34:58,290
They can do all
sorts of chemistry

714
00:34:58,290 --> 00:35:01,280
that we struggle
to be able to do.