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CATHERINE DRENNAN: And
so on today's hand out

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we're continuing to
think about color.

00:00:31.900 --> 00:00:34.690
We're also going to think
about magnetism some more,

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and we're going to think about
more types of geometries.

00:00:38.210 --> 00:00:41.440
So we've seen that the type
of ligand, whether it's

00:00:41.440 --> 00:00:44.230
a weak field, intermediate
field, or strong field ligand

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makes a difference in terms
of the splitting energy.

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How much the d
orbitals are split due

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in the presence of
the ligand, arranged

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in octahedron geometry.

00:00:52.900 --> 00:00:54.994
But we'll see that
the geometry matters.

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That if you have different
kinds of geometries, then

00:00:57.160 --> 00:00:58.743
the splinting is
going to be different

00:00:58.743 --> 00:01:00.340
between the d orbitals.

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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We're going to look at
a nickel demo, which

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we'll have in a few minutes.

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But first, let's think about the
colors that we're going to see.

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So if we have a nickel chloride
compound that is greenish,

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what kind-- it will absorb
then what kind of light,

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if it is a greenish
kind of color?

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What color would it absorb then?

00:01:23.740 --> 00:01:24.520
AUDIENCE: Red.

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CATHERINE DRENNAN: Red.

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Reddish, which is what
kind of wavelength?

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Long or short?

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AUDIENCE: Long.

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CATHERINE DRENNAN: Long.

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Right.

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So we're going to get a
long, reddish kind of-- it

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will absorb a long
or red wavelength.

00:01:35.960 --> 00:01:38.659
And so if we're absorbing
a long wavelength, what

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would be true about
the splitting energies?

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Is it going to be a big
or small splitting energy?

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So first, if you
have long wavelength

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what's the frequency?

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Long or short?

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AUDIENCE: Short.

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CATHERINE DRENNAN: Short.

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And so the energy
would be short as well.

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So it's going to be a small
energy associated with it.

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Just a small splitting.

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And you remember what we
learned about chloride minus?

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What kind of a ligand is it?

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It's a weak field ligand,
so this makes sense.

00:02:07.660 --> 00:02:10.479
So a weak field ligand only
splits the field a little bit,

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it's not a very strong
ligand, so it can only

00:02:12.430 --> 00:02:15.040
split it so much.

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Now we're going to take
this greenish compound

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and we're going to
add some water to it.

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And that's going to make
it a little more blue.

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Be sort of a blue green.

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And let's think about
what's happening there.

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And we'll compare it
to what we have above.

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So now, if it looks blue
green, what sort of color

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is going to be what's absorbed?

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AUDIENCE: Orange red.

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CATHERINE DRENNAN: Right.

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So we're going to have a
more orange red color here.

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And so that's going to be longer
or shorter than the one above?

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AUDIENCE: Shorter.

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CATHERINE DRENNAN: Shorter.

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Right.

00:02:51.180 --> 00:02:52.150
So we were here.

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Now we're moving more
into the orange region,

00:02:54.417 --> 00:02:56.500
so we're going to be
absorbing a wavelength that's

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a bit shorter.

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So is the energy going
to be larger or smaller?

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Yeah.

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So it's going to be a
larger energy because we

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have a shorter
wavelength so we're

00:03:06.040 --> 00:03:07.850
going to have a bit
of a higher frequency.

00:03:07.850 --> 00:03:10.719
And so we'll have a higher
energy or larger energy.

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And do you remember what
kind of ligand water is?

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It's an intermediate
field ligand

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so it's going to be
stronger than chloride.

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So chloride was very weak.

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Water sort of in the middle.

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And then we had cyanide as an
example of a very strong field

00:03:25.690 --> 00:03:27.390
ligand.

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So this makes sense that
would be a bit stronger.

00:03:30.100 --> 00:03:32.080
So we have a larger splitting.

00:03:32.080 --> 00:03:34.810
Now they're going to break
this sample into two.

00:03:34.810 --> 00:03:38.380
And batch one you're
going to add EDTA.

00:03:38.380 --> 00:03:42.040
That was our chelating agent
that we talked about before,

00:03:42.040 --> 00:03:44.680
and that's going to make
it even a bit more blue.

00:03:44.680 --> 00:03:48.700
And here we have our model
of EDTA bound to our metal.

00:03:48.700 --> 00:03:51.460
And so if we think
about this, then

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if it's a bit more
blue-- so we're

00:03:53.980 --> 00:03:57.940
going to be absorbing a color
that's even more orange.

00:03:57.940 --> 00:04:02.120
And so that's going to be even
shorter than what we had there.

00:04:02.120 --> 00:04:07.180
So then our splitting energy--
the energy is going to be what?

00:04:07.180 --> 00:04:08.925
Larger or smaller?

00:04:08.925 --> 00:04:09.841
AUDIENCE: [INAUDIBLE].

00:04:09.841 --> 00:04:10.840
CATHERINE DRENNAN: Yeah.

00:04:10.840 --> 00:04:12.100
So it will be even larger.

00:04:12.100 --> 00:04:15.310
And I've never told you
what kind of ligand EDTA is,

00:04:15.310 --> 00:04:18.190
but from this, if you're
getting a larger splitting,

00:04:18.190 --> 00:04:21.130
you would predict it's a
stronger ligand than water.

00:04:21.130 --> 00:04:24.880
And in fact it is an even
stronger one than water.

00:04:24.880 --> 00:04:28.420
And again, we're going to be
increasing entropy in this room

00:04:28.420 --> 00:04:30.160
in a few minutes
because we're going

00:04:30.160 --> 00:04:33.340
to be displacing six
water molecules with one

00:04:33.340 --> 00:04:35.860
molecule of EDTA, which
will bind to your metal

00:04:35.860 --> 00:04:37.300
with six points of attachment.

00:04:37.300 --> 00:04:40.150
So watch out for
that entropy change.

00:04:40.150 --> 00:04:41.980
So that was batch one.

00:04:41.980 --> 00:04:48.550
Now we're going to take some of
this nickel hexa-aquo compound

00:04:48.550 --> 00:04:51.070
and we're going to mix it
with another chelating agent.

00:04:51.070 --> 00:04:55.030
So remember, our nickel
water complex is blue green

00:04:55.030 --> 00:04:57.790
and we're going to add
another chelating agent,

00:04:57.790 --> 00:05:00.430
and now it's going
to become red.

00:05:00.430 --> 00:05:05.084
And so if it's red, what
color is going to be absorbed?

00:05:05.084 --> 00:05:05.750
AUDIENCE: Green.

00:05:05.750 --> 00:05:06.940
CATHERINE DRENNAN: Green.

00:05:06.940 --> 00:05:08.980
And so this wavelength
then is going

00:05:08.980 --> 00:05:12.330
to be what compared to orange?

00:05:12.330 --> 00:05:14.670
Yeah, so it's even way shorter.

00:05:14.670 --> 00:05:15.970
We were kind of right up here.

00:05:15.970 --> 00:05:19.790
Now we've all the way shifted
down here so it's way shorter.

00:05:19.790 --> 00:05:21.970
So the energy is
going to be what?

00:05:21.970 --> 00:05:23.630
Small or big?

00:05:23.630 --> 00:05:24.366
AUDIENCE: Big.

00:05:24.366 --> 00:05:26.240
CATHERINE DRENNAN: It's
going to be very big.

00:05:26.240 --> 00:05:29.200
But this isn't an
octahedral system anymore,

00:05:29.200 --> 00:05:32.530
so I didn't have a
little O by my energy.

00:05:32.530 --> 00:05:34.960
And it's actually a
square planar system

00:05:34.960 --> 00:05:38.060
so we're not gonna do sort
of a direct comparison here.

00:05:38.060 --> 00:05:40.690
But this tells us
that in square planar

00:05:40.690 --> 00:05:42.940
you're probably going to
get pretty big splitting

00:05:42.940 --> 00:05:46.090
of our d orbital energies
because we can get something

00:05:46.090 --> 00:05:50.710
that-- the color suggests that
there must be a big splitting.

00:05:50.710 --> 00:05:54.490
So those are what we're
predicting for the colors.

00:05:54.490 --> 00:05:55.450
Let's see what happens.

00:06:04.281 --> 00:06:05.280
GUEST SPEAKER: Is it on?

00:06:05.280 --> 00:06:05.640
Yes it is.

00:06:05.640 --> 00:06:06.140
OK.

00:06:06.140 --> 00:06:08.430
So this is the nickel
chloride complex

00:06:08.430 --> 00:06:09.760
that Cathy was talking about.

00:06:09.760 --> 00:06:12.470
As most of us can
see it's very green.

00:06:12.470 --> 00:06:13.350
Put it under here.

00:06:13.350 --> 00:06:16.290
You could probably obviously
see that it's green.

00:06:16.290 --> 00:06:17.895
Maybe against this background.

00:06:17.895 --> 00:06:18.700
Look at that.

00:06:18.700 --> 00:06:19.380
It's very green.

00:06:19.380 --> 00:06:22.570
Thank you, Elena.

00:06:22.570 --> 00:06:24.002
So we don't need that, do we?

00:06:24.002 --> 00:06:24.960
No, we don't need that.

00:06:24.960 --> 00:06:26.626
We're just gonna pour
it into the water.

00:06:26.626 --> 00:06:32.220
So when we pour this
into the water we're

00:06:32.220 --> 00:06:34.010
expecting-- you guys remember?

00:06:34.010 --> 00:06:35.010
Blue green.

00:06:35.010 --> 00:06:38.010
So [INAUDIBLE].

00:06:42.440 --> 00:06:51.804
And that's fuming.

00:07:00.671 --> 00:07:01.171
That smells.

00:07:01.171 --> 00:07:01.671
Terrible.

00:07:05.640 --> 00:07:09.054
And that's very
obviously not that clear.

00:07:09.054 --> 00:07:11.440
[LAUGHTER]

00:07:11.440 --> 00:07:12.060
Wonderful.

00:07:12.060 --> 00:07:14.826
Well, it's kind of blue green.

00:07:14.826 --> 00:07:17.200
Right around the color that
you'd expect for water to be.

00:07:17.200 --> 00:07:18.210
CATHERINE DRENNAN: We
should switch gloves

00:07:18.210 --> 00:07:20.802
from green to blue green
as we do the experiment.

00:07:20.802 --> 00:07:22.760
You can see it a little
bit better there maybe.

00:07:22.760 --> 00:07:24.290
I don't know.

00:07:24.290 --> 00:07:25.320
Trust us.

00:07:25.320 --> 00:07:26.010
GUEST SPEAKER: Now
we're going to do--

00:07:26.010 --> 00:07:28.385
CATHERINE DRENNAN: The next
one's a little more dramatic.

00:07:28.385 --> 00:07:30.187
Front row.

00:07:30.187 --> 00:07:31.710
Is it blue green?

00:07:31.710 --> 00:07:33.274
AUDIENCE: Yeah.

00:07:33.274 --> 00:07:35.190
GUEST SPEAKER: So we're
going to split this up

00:07:35.190 --> 00:07:39.930
into two solutions,
which is about 180 mls.

00:07:42.855 --> 00:07:44.813
I should have picked a
different colored glove.

00:07:50.470 --> 00:07:53.030
And we're going to add
some EDTA-- thank you.

00:07:53.030 --> 00:07:55.540
We're going to add
some EDTA into this.

00:07:55.540 --> 00:07:57.430
And that EDTA is where?

00:07:57.430 --> 00:07:58.700
It's a powder, right?

00:07:58.700 --> 00:08:01.021
So EDTA is relatively
insoluble in water

00:08:01.021 --> 00:08:02.770
so we're going to add
a little bit of base

00:08:02.770 --> 00:08:04.360
to make sure this works.

00:08:04.360 --> 00:08:06.510
That's not the base.

00:08:06.510 --> 00:08:08.180
That's the base.

00:08:08.180 --> 00:08:09.910
So let's start with the EDTA.

00:08:09.910 --> 00:08:12.965
I'm gonna use this
to mix, I think.

00:08:12.965 --> 00:08:14.323
I should mix it with this.

00:08:19.037 --> 00:08:20.993
I should have gotten
something to mix it with.

00:08:23.930 --> 00:08:26.350
I don't think so.

00:08:26.350 --> 00:08:26.850
Watch out.

00:08:26.850 --> 00:08:27.130
Watch out.

00:08:27.130 --> 00:08:28.588
This is going to
be a bit reactive.

00:08:36.312 --> 00:08:38.123
It worked pretty well, actually.

00:08:38.123 --> 00:08:40.062
Look at that.

00:08:40.062 --> 00:08:40.874
Yay.

00:08:40.874 --> 00:08:41.730
It's blue.

00:08:45.175 --> 00:08:46.140
Just a second.

00:08:46.140 --> 00:08:48.540
[LAUGHTER]

00:08:48.540 --> 00:08:53.830
So by comparison it's
a little bit more blue.

00:08:53.830 --> 00:08:57.700
And as we added some
hydroxide-- or not hydroxide,

00:08:57.700 --> 00:09:01.090
acetate-- it allowed the EDTA
to dissolve just a little bit

00:09:01.090 --> 00:09:03.100
more, which is why it reacted.

00:09:03.100 --> 00:09:03.820
OK, cool.

00:09:03.820 --> 00:09:12.200
So now for the last thing we
will add-- what are we adding?

00:09:12.200 --> 00:09:12.700
Oh, right.

00:09:12.700 --> 00:09:13.222
DMG.

00:09:13.222 --> 00:09:15.430
And we apologize to Cathy
because this smells really,

00:09:15.430 --> 00:09:18.009
really bad and she has to smell
this for the next 20 minutes

00:09:18.009 --> 00:09:19.050
along with the front row.

00:09:19.050 --> 00:09:20.383
AUDIENCE: So will the front row.

00:09:20.383 --> 00:09:21.440
GUEST SPEAKER: Sorry.

00:09:21.440 --> 00:09:24.236
But after we pour this
you're not actually

00:09:24.236 --> 00:09:25.944
going to see a whole
lot of color change.

00:09:29.970 --> 00:09:31.890
It smell bad.

00:09:31.890 --> 00:09:35.640
And the reason for that
is because this is not

00:09:35.640 --> 00:09:36.970
quite as good.

00:09:36.970 --> 00:09:41.110
So the DMG has to come in and
actually replace the water,

00:09:41.110 --> 00:09:43.444
and it's actually kind of
hard for DMG to replace water.

00:09:43.444 --> 00:09:45.026
So what we're going
to do now is we're

00:09:45.026 --> 00:09:46.530
going to add a bit of ammonia.

00:09:46.530 --> 00:09:48.490
And the ammonia can
replace the water

00:09:48.490 --> 00:09:51.870
a little better
than the DMG can,

00:09:51.870 --> 00:09:53.740
and the DMG is going
to replace the ammonia.

00:09:53.740 --> 00:09:55.323
And you'll see
something kind of cool.

00:09:55.323 --> 00:09:58.260
It's actually going to
very locally change color,

00:09:58.260 --> 00:10:01.040
and I might actually do this.

00:10:01.040 --> 00:10:02.080
Maybe over here.

00:10:02.080 --> 00:10:03.710
CATHERINE DRENNAN: What to
do it on the document camera?

00:10:03.710 --> 00:10:04.747
GUEST SPEAKER: Is going
to work on the camera?

00:10:04.747 --> 00:10:05.705
CATHERINE DRENNAN: Mhm.

00:10:05.705 --> 00:10:06.940
GUEST SPEAKER: OK.

00:10:06.940 --> 00:10:09.970
And let's give this a shot.

00:10:09.970 --> 00:10:11.640
Well, I can't reach that.

00:10:16.844 --> 00:10:18.760
CATHERINE DRENNAN: You
have to move your hand.

00:10:18.760 --> 00:10:19.690
GUEST SPEAKER: Let me pour it.

00:10:19.690 --> 00:10:21.940
CATHERINE DRENNAN: Yeah, so
you can see the local now.

00:10:26.020 --> 00:10:29.490
GUEST SPEAKER: So it goes
back to being blue green again

00:10:29.490 --> 00:10:32.550
because the concentration
of ammonia that we're adding

00:10:32.550 --> 00:10:36.452
is not quite enough to
counteract the amount of water

00:10:36.452 --> 00:10:37.410
that's already in here.

00:10:37.410 --> 00:10:43.190
But if we add enough eventually
it will turn totally red.

00:10:43.190 --> 00:10:48.452
But for it now you can see it's
an equilibrium reaction, yay.

00:10:52.500 --> 00:10:55.060
CATHERINE DRENNAN: And it talks
about also rates of reactions

00:10:55.060 --> 00:10:58.000
and rates of exchange,
and that's our next unit.

00:10:58.000 --> 00:11:01.500
[LAUGHTER]

00:11:02.970 --> 00:11:05.958
GUEST SPEAKER: Yay.

00:11:05.958 --> 00:11:06.954
[CLASS OOHS]

00:11:06.954 --> 00:11:08.335
GUEST SPEAKER: Aw.

00:11:08.335 --> 00:11:10.501
Well, that's a good lead
in to the next demo, right?

00:11:13.852 --> 00:11:15.060
CATHERINE DRENNAN: All right.

00:11:15.060 --> 00:11:15.896
Thank you guys.

00:11:20.750 --> 00:11:22.680
So you saw that
red color develop,

00:11:22.680 --> 00:11:24.740
and so it's not just
about whether something is

00:11:24.740 --> 00:11:26.240
a strong or weak field ligand.

00:11:26.240 --> 00:11:28.080
It's also about the geometry.

00:11:28.080 --> 00:11:30.610
So we're going to talk later
about square planar geometry,

00:11:30.610 --> 00:11:32.510
so keep in mind that
we'd expect that there

00:11:32.510 --> 00:11:35.390
should be some splitting
between those d orbitals.

00:11:35.390 --> 00:11:38.351
But before we get
to square planar

00:11:38.351 --> 00:11:39.600
we're going to do tetrahedral.

00:11:42.690 --> 00:11:44.850
So here is our
tetrahedral system.

00:11:44.850 --> 00:11:47.240
Here's my little
drawing of tetrahedral,

00:11:47.240 --> 00:11:50.360
and I have my
tetrahedral model here.

00:11:50.360 --> 00:11:54.710
And so here we're going to
have our tetrahedral coordinate

00:11:54.710 --> 00:11:57.080
frame like this, where
we have two ligands

00:11:57.080 --> 00:11:58.830
in the plane of the screen.

00:11:58.830 --> 00:12:01.970
One ligand coming out at you
and one ligand going back.

00:12:01.970 --> 00:12:04.520
And so now we're going
to think about how

00:12:04.520 --> 00:12:08.750
our different sets of d orbitals
are going to be affected

00:12:08.750 --> 00:12:11.420
by tetrahedral geometry.

00:12:11.420 --> 00:12:14.060
And again, remember crystal
field theory is just

00:12:14.060 --> 00:12:17.480
saying that the ligands are
like negative charges pointing

00:12:17.480 --> 00:12:19.170
toward the d orbitals.

00:12:19.170 --> 00:12:21.740
So when the ligand
and the d orbital

00:12:21.740 --> 00:12:23.510
are near each other--
big repulsion.

00:12:23.510 --> 00:12:26.780
When they're farther
away-- less repulsion.

00:12:26.780 --> 00:12:29.690
So let's look at this case now.

00:12:29.690 --> 00:12:33.720
And so here we see
in this geometry

00:12:33.720 --> 00:12:36.470
our ligands are now off axis.

00:12:36.470 --> 00:12:37.980
Here is the z-axis.

00:12:37.980 --> 00:12:39.100
Here's the y-axis.

00:12:39.100 --> 00:12:40.340
Here is the x-axis.

00:12:40.340 --> 00:12:42.230
Our ligands are off axis.

00:12:42.230 --> 00:12:46.100
So our orbital sets that
are also kind of off axis

00:12:46.100 --> 00:12:49.580
are going to be more affected
than our orbital sets that

00:12:49.580 --> 00:12:51.260
were on axis.

00:12:51.260 --> 00:12:53.360
So this is different
from what we saw

00:12:53.360 --> 00:12:55.290
with the octahedral geometry.

00:12:55.290 --> 00:12:58.430
So now we have more repulsion
between those negative point

00:12:58.430 --> 00:13:02.300
charges that are the ligands
and the d orbitals that

00:13:02.300 --> 00:13:03.080
are off axis.

00:13:03.080 --> 00:13:05.340
The ones that are
45 degrees away.

00:13:05.340 --> 00:13:11.420
So our dyz, dzy, and dxz.

00:13:11.420 --> 00:13:15.170
So this is, in
fact, the opposite

00:13:15.170 --> 00:13:18.950
of the octahedral case
because in the octahedral case

00:13:18.950 --> 00:13:21.530
we had-- the
ligands were on axis

00:13:21.530 --> 00:13:24.470
and so the orbitals that were
on axes were the most affected.

00:13:24.470 --> 00:13:27.320
But now with tetrahedral
ligand's off axis so

00:13:27.320 --> 00:13:30.270
the orbitals that are off
axis are the most effective.

00:13:30.270 --> 00:13:35.090
So these switch positions now.

00:13:35.090 --> 00:13:40.730
And dx squared minus
y squared dz squared.

00:13:40.730 --> 00:13:42.540
They still have the same energy.

00:13:42.540 --> 00:13:45.020
They're still degenerate
with respect to each other,

00:13:45.020 --> 00:13:48.500
but now these are stabilized
compared to these.

00:13:48.500 --> 00:13:50.450
But they also have
the same energy.

00:13:50.450 --> 00:13:52.700
So all of these
three orbital sets

00:13:52.700 --> 00:13:54.140
are also at the same energy.

00:13:54.140 --> 00:13:56.840
Also degenerate.

00:13:56.840 --> 00:13:59.390
Now, one other really important
thing about tetrahedral

00:13:59.390 --> 00:14:03.200
is not only is it the opposite
of octahedral in terms

00:14:03.200 --> 00:14:07.010
of where those orbitals
are, but overall they're

00:14:07.010 --> 00:14:08.720
sort of less splitting.

00:14:08.720 --> 00:14:13.790
So even though the orbitals
that are kind of off axis

00:14:13.790 --> 00:14:16.670
are more affected by
that tetrahedral geometry

00:14:16.670 --> 00:14:19.490
than the others,
still the ligands

00:14:19.490 --> 00:14:22.310
aren't really pointing right
toward those orbitals at all.

00:14:22.310 --> 00:14:24.200
They're closer but
they're not right at them.

00:14:24.200 --> 00:14:27.560
So it's very different
from the octahedral case

00:14:27.560 --> 00:14:32.000
where you had the orbitals
sort of right on axis

00:14:32.000 --> 00:14:33.650
and the ligands right on axis.

00:14:33.650 --> 00:14:35.270
So there's less splitting.

00:14:35.270 --> 00:14:37.130
It's smaller splitting.

00:14:37.130 --> 00:14:40.610
So the octahedral, or the
tetrahedral crystal field

00:14:40.610 --> 00:14:43.640
splitting energy,
is this delta sub t.

00:14:43.640 --> 00:14:45.950
And that's going to be smaller.

00:14:45.950 --> 00:14:48.440
So let's look now at some
crystal field splitting

00:14:48.440 --> 00:14:49.940
diagrams.

00:14:49.940 --> 00:14:52.880
I'm going to compare
the octahedral case

00:14:52.880 --> 00:14:54.770
with the tetrahedral case.

00:14:54.770 --> 00:14:57.590
So here is our
octahedral case again.

00:14:57.590 --> 00:15:00.620
We have our octahedral crystal
field splitting energy--

00:15:00.620 --> 00:15:04.160
our delta O. Now we have our
tetrahedral crystal field

00:15:04.160 --> 00:15:07.010
splitting energy-- delta t.

00:15:07.010 --> 00:15:11.510
And we see again that
it's opposite orders.

00:15:11.510 --> 00:15:14.640
So our dx squared
minus y squared

00:15:14.640 --> 00:15:18.260
dz squared, instead of being up
here as it is with octahedral,

00:15:18.260 --> 00:15:20.030
is now down here.

00:15:20.030 --> 00:15:23.870
And instead of our EG
we now just have E.

00:15:23.870 --> 00:15:26.360
We just lost the G here.

00:15:26.360 --> 00:15:30.620
And our three sets that
were stabilized, compared

00:15:30.620 --> 00:15:33.640
to the hypothetical
spherical crystal field,

00:15:33.640 --> 00:15:38.030
are now de-stabilized because
those orbitals at 45 degrees

00:15:38.030 --> 00:15:40.880
are closer to our
tetrahedral ligands.

00:15:40.880 --> 00:15:43.530
So again, we have this switch.

00:15:43.530 --> 00:15:49.532
And again, our EG goes to just
G. The book sometimes has E2.

00:15:49.532 --> 00:15:51.740
I don't know where that came
from but you should just

00:15:51.740 --> 00:15:52.239
ignore it.

00:15:52.239 --> 00:15:58.040
It's just E. And T2G
is now is just T2.

00:15:58.040 --> 00:16:00.830
So again, you can
see in this picture

00:16:00.830 --> 00:16:04.400
really well-- splitting energy
is a lot less for tetrahedral.

00:16:04.400 --> 00:16:07.880
This is much smaller than
the octahedral crystal field

00:16:07.880 --> 00:16:11.054
splitting energy, so much,
much smaller because again,

00:16:11.054 --> 00:16:12.470
none of those
ligand point charges

00:16:12.470 --> 00:16:14.540
are really directly
toward those orbitals.

00:16:14.540 --> 00:16:17.270
So overall, it's less splitting.

00:16:17.270 --> 00:16:20.420
And because there's
less splitting, when

00:16:20.420 --> 00:16:24.620
you think about putting
electrons in to the system

00:16:24.620 --> 00:16:27.350
it doesn't take
much to go up here.

00:16:27.350 --> 00:16:29.390
So the pairing energies
is going to always

00:16:29.390 --> 00:16:33.920
be a lot greater than the energy
to put it in this higher energy

00:16:33.920 --> 00:16:35.810
orbital set because
it's not very much

00:16:35.810 --> 00:16:37.520
higher than the first set.

00:16:37.520 --> 00:16:40.340
So these would all
be high spin systems.

00:16:40.340 --> 00:16:42.440
So we put in our
electrons singly

00:16:42.440 --> 00:16:47.750
to the fullest extent possible
before we start to pair them.

00:16:47.750 --> 00:16:50.660
So you can assume that
all tetrahedral complexes

00:16:50.660 --> 00:16:51.650
are high spins.

00:16:51.650 --> 00:16:54.650
That's a pretty good assumption.

00:16:54.650 --> 00:16:57.710
So just like the
tetrahedral case,

00:16:57.710 --> 00:16:59.630
we have overall--
we're maintaining

00:16:59.630 --> 00:17:01.770
the energy of the system.

00:17:01.770 --> 00:17:04.910
So in the tetrahedral
case we had three orbitals

00:17:04.910 --> 00:17:06.849
that were stabilized.

00:17:06.849 --> 00:17:11.780
So they went down by
2/5 and two that went up

00:17:11.780 --> 00:17:14.030
were de-stabilized,
so they went up

00:17:14.030 --> 00:17:17.690
by 3/5 to maintain the
overall energy of the system.

00:17:17.690 --> 00:17:21.470
In the tetrahedral case
we have two orbitals

00:17:21.470 --> 00:17:23.359
that are stabilized
down in energy,

00:17:23.359 --> 00:17:26.270
so they're down by minus 3/5.

00:17:26.270 --> 00:17:29.600
And then we have three up,
so those are up by 2/5.

00:17:29.600 --> 00:17:34.790
So same idea, but again,
everything is opposite.

00:17:34.790 --> 00:17:36.950
So let's take a
look at an example

00:17:36.950 --> 00:17:43.850
of the tetrahedral case, and
we'll look at chromium 3 plus.

00:17:43.850 --> 00:17:47.960
So what is the d count here?

00:17:47.960 --> 00:17:49.850
Who can just tell me?

00:17:49.850 --> 00:17:51.285
Find chromium in our table.

00:17:54.390 --> 00:17:54.890
Yup.

00:17:54.890 --> 00:17:59.680
It's going to be three,
so group 6 minus 3 is 3.

00:17:59.680 --> 00:18:02.000
And now, why don't
you tell me how

00:18:02.000 --> 00:18:06.010
we are going to put in
those three electrons?

00:18:15.781 --> 00:18:16.280
All right.

00:18:16.280 --> 00:18:17.170
10 more seconds.

00:18:31.440 --> 00:18:32.110
OK.

00:18:32.110 --> 00:18:33.800
Most people got that right.

00:18:33.800 --> 00:18:37.820
So again, this is not correct
for a high spin, which

00:18:37.820 --> 00:18:40.190
most tetrahedral compounds are.

00:18:40.190 --> 00:18:41.490
This would be correct.

00:18:41.490 --> 00:18:43.910
This arrangement of
electrons is also correct,

00:18:43.910 --> 00:18:48.200
but if you look at the orbital
names those are incorrect.

00:18:48.200 --> 00:18:52.340
So on a test you need
to be able to write

00:18:52.340 --> 00:18:55.670
all the correct orbital names
and the correct designators

00:18:55.670 --> 00:18:58.580
as well, as well as
putting it in the electrons

00:18:58.580 --> 00:18:59.570
in the right way.

00:18:59.570 --> 00:19:01.670
So good to practice.

00:19:01.670 --> 00:19:06.840
So we put in now our
three electrons over here,

00:19:06.840 --> 00:19:11.520
and now we can think about
our dn configuration.

00:19:11.520 --> 00:19:13.970
So if you're asked to
write out the d to the n

00:19:13.970 --> 00:19:17.930
electron configuration,
what that's asking you for

00:19:17.930 --> 00:19:21.830
is to say how many electrons
are in which of the two

00:19:21.830 --> 00:19:23.180
orbital levels.

00:19:23.180 --> 00:19:27.890
And so you would say, in the
e level here you have two

00:19:27.890 --> 00:19:31.100
and in the t2
level you have one.

00:19:31.100 --> 00:19:32.720
And this is just
then a shorthand.

00:19:32.720 --> 00:19:35.030
That's why they have these
little abbreviations.

00:19:35.030 --> 00:19:40.190
You don't have to write out all
the names of your d orbitals.

00:19:40.190 --> 00:19:44.870
So how many unpaired
electrons do we have then?

00:19:44.870 --> 00:19:46.720
We have what?

00:19:46.720 --> 00:19:48.140
Three.

00:19:48.140 --> 00:19:55.370
And if I'm now telling you that
this is a complex with chloride

00:19:55.370 --> 00:19:58.520
and that the wavelength of the
most intensely absorbed light

00:19:58.520 --> 00:20:01.730
is 740, why don't
you predict the color

00:20:01.730 --> 00:20:03.040
of the complex for me?

00:20:12.451 --> 00:20:12.950
OK.

00:20:12.950 --> 00:20:13.775
10 more seconds.

00:20:27.120 --> 00:20:29.440
Yup.

00:20:29.440 --> 00:20:32.830
So we can look and
see this wavelength

00:20:32.830 --> 00:20:36.010
is going to be in the red
so that the predictive color

00:20:36.010 --> 00:20:40.870
of the complex would be the
complimentary, or green.

00:20:40.870 --> 00:20:48.320
And so green then is one
that has-- it's pretty short.

00:20:48.320 --> 00:20:49.960
This is a pretty
long wavelength,

00:20:49.960 --> 00:20:53.237
which would be consistent with
a very tiny splitting energy.

00:20:57.190 --> 00:20:59.770
So now let's think about
the square planar case.

00:21:02.720 --> 00:21:07.850
So our square planar
system is described--

00:21:07.850 --> 00:21:10.240
so we're in the plane here.

00:21:10.240 --> 00:21:12.290
It's, again, square planar.

00:21:12.290 --> 00:21:17.180
And now we have our
ligands along the y-axis

00:21:17.180 --> 00:21:18.870
and the x-axis.

00:21:18.870 --> 00:21:22.710
So we have nothing
along the z-axis here.

00:21:22.710 --> 00:21:26.540
So tell me, based on this
and then again our ligands

00:21:26.540 --> 00:21:30.950
are on axis, which
of those d orbitals

00:21:30.950 --> 00:21:33.050
do you think is
going to be the most

00:21:33.050 --> 00:21:35.630
de-stabilized by this geometry?

00:21:35.630 --> 00:21:38.050
What do you think?

00:21:38.050 --> 00:21:39.504
You can just yell it out.

00:21:39.504 --> 00:21:41.395
AUDIENCE: x squared
minus y squared.

00:21:41.395 --> 00:21:43.770
CATHERINE DRENNAN: x
squared minus y squared.

00:21:43.770 --> 00:21:46.320
And what would you think
would be next in terms

00:21:46.320 --> 00:21:50.690
of de-stabilized of those sets?

00:21:50.690 --> 00:21:51.740
xy?

00:21:51.740 --> 00:21:54.150
Yeah, so that's the case.

00:21:54.150 --> 00:21:57.350
So most is going to be dx
squared minus y squared.

00:21:57.350 --> 00:21:59.420
Again, those
orbitals are on axes.

00:21:59.420 --> 00:22:00.770
ligands on axis.

00:22:00.770 --> 00:22:04.190
Next would be the other
one that has x and y.

00:22:04.190 --> 00:22:06.380
So let's take a
look at this now.

00:22:06.380 --> 00:22:10.970
So we have our dx
squared minus y squared.

00:22:10.970 --> 00:22:12.470
Our orbitals are on axis.

00:22:12.470 --> 00:22:13.760
Our ligands are on axis.

00:22:13.760 --> 00:22:16.320
You really have
lots of repulsion.

00:22:16.320 --> 00:22:19.320
So this would be de-stabilized
the most compared

00:22:19.320 --> 00:22:21.290
to all other d orbitals.

00:22:21.290 --> 00:22:24.260
Really different amount
of destabilization.

00:22:24.260 --> 00:22:26.420
This is a lot of repulsion.

00:22:26.420 --> 00:22:29.660
All the ligands are right
toward those orbitals.

00:22:29.660 --> 00:22:33.740
So dz squared, which
used to be degenerate

00:22:33.740 --> 00:22:37.680
with dx squared minus y
squared now is not anymore.

00:22:37.680 --> 00:22:39.840
There's a lot less
repulsion for this

00:22:39.840 --> 00:22:45.020
because there's no ligands
along the z-axis anymore.

00:22:45.020 --> 00:22:47.180
So let's look at our
other orbital set.

00:22:47.180 --> 00:22:51.950
The next one in terms of
being de-stabilized is dxy.

00:22:51.950 --> 00:22:55.670
Now, these orbitals are off axis
so it's not nearly as bad as

00:22:55.670 --> 00:22:58.340
for dx squared minus y squared.

00:22:58.340 --> 00:23:01.290
But compared to
everything else it's

00:23:01.290 --> 00:23:03.890
a lot more repulsion
than everybody else,

00:23:03.890 --> 00:23:08.780
but it's less than our dx
squared minus y squared.

00:23:08.780 --> 00:23:10.940
And these guys are then
going to be stabilized

00:23:10.940 --> 00:23:13.010
compared to the others.

00:23:13.010 --> 00:23:16.010
So let's now draw our
splitting diagrams

00:23:16.010 --> 00:23:19.460
and think about how this
all plays in together.

00:23:19.460 --> 00:23:22.640
And so again, we'll compare
it to our octahedral crystal

00:23:22.640 --> 00:23:24.080
field.

00:23:24.080 --> 00:23:29.750
So now, the most de-stabilized
way up here, which

00:23:29.750 --> 00:23:33.460
is this orbital going to be?

00:23:33.460 --> 00:23:34.720
Which one?

00:23:34.720 --> 00:23:36.271
x squared minus y squared.

00:23:36.271 --> 00:23:36.770
Right.

00:23:36.770 --> 00:23:40.130
That's up in energy the
most, so most de-stabilized.

00:23:40.130 --> 00:23:43.640
It's experiencing
the most repulsion.

00:23:43.640 --> 00:23:49.190
And then next, but
much lower down, dxy.

00:23:49.190 --> 00:23:52.740
Again, the ligands are
along in the xy plane,

00:23:52.740 --> 00:23:53.820
so that would be second.

00:23:53.820 --> 00:23:58.280
But those are 45 degrees off
axis so it's way down in energy

00:23:58.280 --> 00:24:00.890
compared to the ones
that are on axis.

00:24:00.890 --> 00:24:03.840
And then down here we
kind of have all the rest,

00:24:03.840 --> 00:24:08.090
and it's usually written
with dz squared here

00:24:08.090 --> 00:24:14.050
and then dyz and dxz over here.

00:24:14.050 --> 00:24:16.580
But the order here--
these are all kind of

00:24:16.580 --> 00:24:20.010
stabilized compared to these
two and the exact order

00:24:20.010 --> 00:24:24.800
is not quite as firm as in
octahedral or tetrahedral

00:24:24.800 --> 00:24:25.850
cases.

00:24:25.850 --> 00:24:28.430
So again, this is
quite different now.

00:24:28.430 --> 00:24:32.340
Overall, the energy
is also maintained,

00:24:32.340 --> 00:24:34.485
but there's too many
orbitals in too many places

00:24:34.485 --> 00:24:36.840
so you're not
expected to know that.

00:24:36.840 --> 00:24:38.960
But one thing that
I will point out

00:24:38.960 --> 00:24:41.850
is that remember for
the demo square planar--

00:24:41.850 --> 00:24:44.390
we said that had to have
a pretty big splitting?

00:24:44.390 --> 00:24:47.660
That's a really big splitting
of the energy of the orbital.

00:24:47.660 --> 00:24:50.030
So square planar
complexes can be

00:24:50.030 --> 00:24:53.570
capable of having
big energies-- you

00:24:53.570 --> 00:24:55.880
need a big energy
of your photon to be

00:24:55.880 --> 00:24:57.179
absorbed by a square planar.

00:24:57.179 --> 00:24:59.720
Or you could if you're going to
bump it all the way up there.

00:24:59.720 --> 00:25:02.780
That's really far away.

00:25:02.780 --> 00:25:06.840
So now, clicker.

00:25:06.840 --> 00:25:09.440
Why don't you tell
me what you think

00:25:09.440 --> 00:25:12.530
of a square pyramidal case?

00:25:12.530 --> 00:25:17.690
And this would be this case
here where you have one ligand.

00:25:17.690 --> 00:25:20.130
You have a square planar
geometry, basically,

00:25:20.130 --> 00:25:22.620
that you've added
an extra ligand too.

00:25:22.620 --> 00:25:24.760
Or you had octahedral
you took one away,

00:25:24.760 --> 00:25:27.021
and that extra ligand
is along the z-axis.

00:25:27.021 --> 00:25:28.770
So what things do you
think would be true?

00:25:39.729 --> 00:25:41.270
Since we're running
out of time let's

00:25:41.270 --> 00:25:42.610
just take 10 more seconds.

00:26:00.320 --> 00:26:04.940
So just to put--
that would be true.

00:26:04.940 --> 00:26:08.330
Now there's a ligand
along z, so dz squared

00:26:08.330 --> 00:26:11.570
is going to be de-stabilized
in the square pyramidal case

00:26:11.570 --> 00:26:13.910
compared to the square planar.

00:26:13.910 --> 00:26:18.410
Everything that has z's in it
would also be de-stabilized,

00:26:18.410 --> 00:26:21.250
and these would definitely
not be degenerate.

00:26:21.250 --> 00:26:24.560
There's no reason they would
have the same energy there.

00:26:24.560 --> 00:26:26.850
So we'll get to our
bio example on Monday,

00:26:26.850 --> 00:26:30.530
but first what are the results?

00:26:30.530 --> 00:26:34.030
[CHEERING]

00:26:40.745 --> 00:26:41.245
Awesome.

00:26:46.400 --> 00:26:47.650
Congratulations.

00:26:47.650 --> 00:26:50.042
That was unexpected.

00:26:50.042 --> 00:26:53.190
Two new groups.

00:26:53.190 --> 00:26:53.690
All right.

00:26:53.690 --> 00:26:54.780
Have a good weekend.

00:26:54.780 --> 00:26:56.900
See you Monday.

00:26:56.900 --> 00:27:03.460
So end of lecture 29 last page.

00:27:03.460 --> 00:27:05.600
We were talking about
biological examples.

00:27:05.600 --> 00:27:07.280
We were talking about
transition metals.

00:27:07.280 --> 00:27:10.220
We're talking about
colors of things.

00:27:10.220 --> 00:27:14.030
And I just wanted to give
you an example of why

00:27:14.030 --> 00:27:16.490
geometry can matter
or be interesting

00:27:16.490 --> 00:27:18.920
from a biological context.

00:27:18.920 --> 00:27:22.850
So the video that you
heard about nickel

00:27:22.850 --> 00:27:26.090
showed that nickel
allows H.pylori

00:27:26.090 --> 00:27:31.100
to colonize your stomach because
the nickel enzyme creates

00:27:31.100 --> 00:27:33.860
a buffering system so
that it can survive

00:27:33.860 --> 00:27:35.710
in the low pH of your stomach.

00:27:35.710 --> 00:27:38.870
And it's very hard to
treat H.pylori infections

00:27:38.870 --> 00:27:41.330
because the antibiotics
that you would

00:27:41.330 --> 00:27:44.690
give to kill the
bacteria get destroyed

00:27:44.690 --> 00:27:48.320
in acidity of the stomach,
so it's a very hard problem.

00:27:48.320 --> 00:27:51.290
And it's fascinating that they
can use this nickel enzyme

00:27:51.290 --> 00:27:54.150
to kind of allow themselves
to live in this environment,

00:27:54.150 --> 00:27:55.280
so that's pretty cool.

00:27:55.280 --> 00:27:58.040
This is also really
cool and arguably more

00:27:58.040 --> 00:27:59.810
beneficial to mankind.

00:27:59.810 --> 00:28:02.330
So nickel dependent
enzymes also are

00:28:02.330 --> 00:28:05.570
responsible for removing a lot
of carbon monoxide and carbon

00:28:05.570 --> 00:28:07.580
dioxide from the environment.

00:28:07.580 --> 00:28:11.330
So microbes have
these enzymes that

00:28:11.330 --> 00:28:13.670
allow them to use carbon
monoxide and carbon

00:28:13.670 --> 00:28:17.780
dioxide as their carbon
source for metabolism.

00:28:17.780 --> 00:28:20.900
And so collectively,
these microbes

00:28:20.900 --> 00:28:23.780
are estimated to remove about
100 million tons of carbon

00:28:23.780 --> 00:28:26.000
monoxide from the
environment every year

00:28:26.000 --> 00:28:29.150
and produce about 1 trillion
kilograms of acetate

00:28:29.150 --> 00:28:32.090
from greenhouse and
other gases, such as CO2.

00:28:32.090 --> 00:28:36.579
So there's a lot of benefit to
us from these nickel enzymes.

00:28:36.579 --> 00:28:38.120
And so people are
interested in doing

00:28:38.120 --> 00:28:39.309
a couple different things.

00:28:39.309 --> 00:28:40.850
One thing they're
interested in doing

00:28:40.850 --> 00:28:42.740
is to see what
these nickel centers

00:28:42.740 --> 00:28:45.830
look like so that they can
make small molecules to do

00:28:45.830 --> 00:28:47.210
the same chemistry.

00:28:47.210 --> 00:28:51.950
People are also interested in
taking these microbes as such

00:28:51.950 --> 00:28:55.190
and getting them to
overexpress these enzymes

00:28:55.190 --> 00:28:59.060
and then convert things
like CO2, greenhouse gas,

00:28:59.060 --> 00:29:00.420
into biofuels.

00:29:00.420 --> 00:29:02.240
So some people in
chemical engineering

00:29:02.240 --> 00:29:06.290
are doing that right now, and
I'm collaborating with them

00:29:06.290 --> 00:29:07.860
on some of these projects.

00:29:07.860 --> 00:29:10.940
So this is, again, a very--
everyone is very concerned

00:29:10.940 --> 00:29:15.532
about climate and so this
is a hot area of research.

00:29:15.532 --> 00:29:17.990
So of course, if you want to
know what something looks like

00:29:17.990 --> 00:29:20.180
at atomic level,
x-ray crystallography

00:29:20.180 --> 00:29:21.720
is a great thing to do.

00:29:21.720 --> 00:29:24.510
But if you don't have
a crystal structure

00:29:24.510 --> 00:29:26.660
you can use spectroscopy.

00:29:26.660 --> 00:29:28.190
In particular, you
can think about

00:29:28.190 --> 00:29:31.640
whether the enzyme
and this nickel center

00:29:31.640 --> 00:29:34.520
is paramagnetic or
diamagnetic, and that

00:29:34.520 --> 00:29:37.680
can help you guess what the
geometry of the metal center

00:29:37.680 --> 00:29:38.180
is.

00:29:38.180 --> 00:29:39.920
So this is sort of
a first experiment

00:29:39.920 --> 00:29:41.750
you might try to
do to understand

00:29:41.750 --> 00:29:44.870
what's going on in your enzyme.

00:29:44.870 --> 00:29:48.410
So say you have a nickel
plus 2 or d8 center

00:29:48.410 --> 00:29:50.930
and it's found to
be diamagnetic.

00:29:50.930 --> 00:29:54.380
Then we could be asked,
can you rule in or out

00:29:54.380 --> 00:29:56.750
some of the common
geometries for nickel

00:29:56.750 --> 00:29:59.640
based on this
single observation?

00:29:59.640 --> 00:30:01.880
So let's do that.

00:30:01.880 --> 00:30:04.410
So we want to add
some electrons.

00:30:04.410 --> 00:30:07.700
So I'm going to go over
here, and I have our diagrams

00:30:07.700 --> 00:30:08.900
on the board.

00:30:08.900 --> 00:30:12.320
So first, octahedral
is a common geometry.

00:30:12.320 --> 00:30:17.690
Does it matter if this has a
big splitting or small splitting

00:30:17.690 --> 00:30:20.160
for a d8 center?

00:30:20.160 --> 00:30:21.670
What do you think?

00:30:21.670 --> 00:30:25.100
Think about it for a minute.

00:30:25.100 --> 00:30:26.840
Let's try it and see.

00:30:26.840 --> 00:30:30.620
So if we have a
small splitting we

00:30:30.620 --> 00:30:33.320
would go-- we put in
our three electrons.

00:30:33.320 --> 00:30:36.600
And again, this is a d8 system,
so we have eight electrons.

00:30:36.600 --> 00:30:38.300
We put in our three
and now we have

00:30:38.300 --> 00:30:40.790
to decide if we're
going to go up here

00:30:40.790 --> 00:30:42.440
or if we're going to pair.

00:30:42.440 --> 00:30:46.180
But let's pretend it's
a small splitting,

00:30:46.180 --> 00:30:48.700
so we'll put an
electron up here.

00:30:48.700 --> 00:30:49.820
Than we're done.

00:30:49.820 --> 00:30:52.601
Now we have to pair, so we're
going to come back down here

00:30:52.601 --> 00:30:55.100
to pair because we're going to
put them in the lowest energy

00:30:55.100 --> 00:30:56.030
orbitals.

00:30:56.030 --> 00:30:59.970
So we have five, six, seven,
eight, and we're done.

00:30:59.970 --> 00:31:02.510
Now, if we said that
the splitting was big

00:31:02.510 --> 00:31:05.810
we would have paired all
of these electrons first

00:31:05.810 --> 00:31:09.819
and then put two electrons
singly at the upper level.

00:31:09.819 --> 00:31:11.360
And that would have
given us actually

00:31:11.360 --> 00:31:13.890
the exact same diagram.

00:31:13.890 --> 00:31:15.530
So in this particular
case, it doesn't

00:31:15.530 --> 00:31:19.460
matter whether there's a big
splitting or a small splitting.

00:31:19.460 --> 00:31:22.790
You get the same
electron configuration.

00:31:22.790 --> 00:31:27.077
So is this diamagnetic
or paramagnetic?

00:31:27.077 --> 00:31:28.035
AUDIENCE: Paramagnetic.

00:31:28.035 --> 00:31:29.540
CATHERINE DRENNAN: Paramagnetic.

00:31:29.540 --> 00:31:30.620
Which means what?

00:31:35.520 --> 00:31:39.050
It means that you have
unpaired electrons.

00:31:39.050 --> 00:31:42.910
So we have unpaired electrons
so it's paramagnetic.

00:31:42.910 --> 00:31:47.410
So let's look at the
square planar system now.

00:31:47.410 --> 00:31:51.910
So we have three orbitals
that are down in energy,

00:31:51.910 --> 00:31:57.130
and because our square planar
system is in the xy plane

00:31:57.130 --> 00:31:59.740
and it's on axis and we
have-- so our ligand's

00:31:59.740 --> 00:32:04.690
on axis and our
ligands on axis point

00:32:04.690 --> 00:32:06.490
toward the orbitals on axis.

00:32:06.490 --> 00:32:10.750
So dx squared minus y squared
is really high in energy.

00:32:10.750 --> 00:32:13.180
xy is a little bit
higher, and these guys

00:32:13.180 --> 00:32:14.620
are down at the bottom.

00:32:14.620 --> 00:32:16.816
So we don't really know
anything about where

00:32:16.816 --> 00:32:18.940
we're going to put them
in, but let's just put them

00:32:18.940 --> 00:32:20.600
in singly in these lower ones.

00:32:20.600 --> 00:32:26.160
So we'll do one, two, three,
and then we'll pair them up.

00:32:26.160 --> 00:32:28.136
Four, five, six.

00:32:28.136 --> 00:32:32.870
And then we have two more,
so that's seven, eight.

00:32:32.870 --> 00:32:35.860
And we definitely, unless
we absolutely have to,

00:32:35.860 --> 00:32:38.860
don't want to put any
electrons in our dx squared

00:32:38.860 --> 00:32:39.822
minus y squared.

00:32:39.822 --> 00:32:41.530
That's way up in
energy, so we don't want

00:32:41.530 --> 00:32:43.930
to do that unless we have to.

00:32:43.930 --> 00:32:46.990
So is this paramagnetic
or diamagnetic?

00:32:46.990 --> 00:32:47.910
AUDIENCE: Diamagnetic.

00:32:47.910 --> 00:32:49.201
CATHERINE DRENNAN: Diamagnetic.

00:32:49.201 --> 00:32:52.030
So we have one
option here that is

00:32:52.030 --> 00:32:56.620
consistent with
the spectroscopy.

00:32:56.620 --> 00:32:58.960
Now let's look at tetrahedral.

00:32:58.960 --> 00:33:01.300
Is tetrahedral--
what do you think?

00:33:01.300 --> 00:33:03.160
Is it going to be
high spin or low spin?

00:33:05.740 --> 00:33:08.380
High spin so we'll
have a small splitting,

00:33:08.380 --> 00:33:12.100
and that is because in
the tetrahedral geometry

00:33:12.100 --> 00:33:15.250
you have-- your
ligands are off axis,

00:33:15.250 --> 00:33:18.580
so we have an opposite
of the octahedral system.

00:33:18.580 --> 00:33:21.730
The orbitals that were higher
in energy, more destabilized,

00:33:21.730 --> 00:33:22.930
are now lower.

00:33:22.930 --> 00:33:25.480
But the ligands aren't
really pointing directly

00:33:25.480 --> 00:33:29.080
toward any of the d orbitals,
so the splitting overall

00:33:29.080 --> 00:33:30.530
is much smaller.

00:33:30.530 --> 00:33:34.000
So this splitting is always
going to be pretty small,

00:33:34.000 --> 00:33:36.190
and so that leads to
a high spin system,

00:33:36.190 --> 00:33:39.560
which is you have the maximum
number of unpaired electrons.

00:33:39.560 --> 00:33:43.030
So you can always assume
it's high spin or splitting

00:33:43.030 --> 00:33:45.220
is small, so we're going
to put your electrons

00:33:45.220 --> 00:33:48.790
in singly to the fullest extent
possible before you pair.

00:33:48.790 --> 00:33:57.550
So we'll put one, two, three,
four, five, six, seven, eight.

00:33:57.550 --> 00:34:00.070
So is this diamagnetic
or paramagnetic?

00:34:00.070 --> 00:34:01.120
AUDIENCE: Paramagnetic.

00:34:01.120 --> 00:34:02.453
CATHERINE DRENNAN: Paramagnetic.

00:34:07.500 --> 00:34:11.310
So of these three
choices, the only one

00:34:11.310 --> 00:34:14.489
that would be consistent
with the spectroscopy

00:34:14.489 --> 00:34:18.600
is the square planar system, and
that turned out to be correct.

00:34:18.600 --> 00:34:22.420
It was a square planar system.

00:34:22.420 --> 00:34:26.739
And so here is a picture of
that square planar system.

00:34:26.739 --> 00:34:28.980
So here we have the
nickel in the middle

00:34:28.980 --> 00:34:33.210
and we have four ligands
all in one plane.

00:34:33.210 --> 00:34:36.840
So we have this really
nice square planar geometry

00:34:36.840 --> 00:34:39.870
that people predicted
would exist before there

00:34:39.870 --> 00:34:41.500
was a crystal structure.

00:34:41.500 --> 00:34:45.030
And so this is one of the
catalysts for allowing microbes

00:34:45.030 --> 00:34:49.080
to live on carbon dioxide as
their carbon source, which

00:34:49.080 --> 00:34:53.850
is really an incredible thing
that an organism can do.

00:34:53.850 --> 00:34:56.650
Little microbes,
bacteria-- super cool.

00:34:56.650 --> 00:34:58.290
They can do all
sorts of chemistry

00:34:58.290 --> 00:35:01.280
that we struggle
to be able to do.