[CrO4]2-
t2 orbitals
(antibonding)
e orbitals
(antibonding)
CT
Energy
Metal (Cr) d-orbitals
Nonbonding
Oxygen 2p MO’s
e orbitals
(bonding)
12 Oxygen 2p orbitals
(4 oxygens x 3 p orbitals)
t2 orbitals
(bonding)
CT ~ 3.3 eV (~375 nm)
Absorption = Violet
Color = Yellow
PbCrO4
Absorption Spectra CrO42- Solutions
0.8
0.7
375 nm light
0.6
absorbance
0.5
0.4
CT1
0.3
0.2
0.1
0
250
300
350
400
450
500
550
600
650
700
750
wavelength (nm)
1
Absorption Spectra CrO42- Solutions
0.8
0.7
0.6
270 nm light
0.4
CT2
0.3
0.2
0.1
0
250
300
350
400
450
500
550
600
650
700
750
wavelength (nm)
What about Chromate Salts?
1.2
5
conc.
2CrO4
solution
SrCrO4
1.0
PbCrO4
2-
0.8
2-
dilute CrO4
solution
3
0.6
2
0.4
absorbance (SrCrO4, PbCrO4)
4
absorbance (CrO4 )
absorbance
0.5
1
0.2
0.0
250
300
350
400
450
500
550
600
650
0
700
wavelength (nm)
SrCrO4 behaves much like a concentrated CrO42- solution. Sr2+ ions have little
effect on the band gap, whereas Pb2+ ions do impact the band gap.
2
A2+CrO4 vs. A2+MoO4 Salts
5.0
4.5
Absorbance (F(R))
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
200
250
300
350
400
450
500
550
600
650
700
750
wavelength (nm)
PbCrO4
Eg = 2.4 eV
SrCrO4
Eg = 2.7 eV
Antibonding (e)
Cr dx2-y2, dz2
CT
PbMoO4
Eg = 3.3 eV
SrMoO4
Eg = 4.3 eV
Antibonding (e)
Mn dx2-y2, dz2
CT
Nonbonding O 2p
Nonbonding O 2p
[CrO4]2-
[MnO4]-
Cation oxidation state increases Cr(VI) → Mn(VII)
d-orbitals become more electronegative (lower in energy)
CT Energy Gap decreases
Absorption shifts to longer wavelengths
3
Antibonding (e)
Mo dx2-y2, dz2
Antibonding (e)
Cr dx2-y2, dz2
CT
CT
Nonbonding O 2p
Nonbonding O 2p
[CrO4]2-
[MoO4]2-
Mo 4d orbitals are larger than the Cr 3d orbitals
d-orbitals interact more with O 2p orbitals – more antibonding
CT Energy Gap increases
Absorption shifts to shorter wavelengths
2nd & 3rd Row Transition Metals
eg (σ*)
2nd row (Y(Y-Cd)
Cd) and 3rd
row (LuHg)
transition
(Lu
metals
•d-orbitals are larger
•Metal-ligand antibonding
interactions are stronger
•eg (σ*) orbitals are more
antibonding
[Co(H2O)6]3+
•Low spin configurations
are always observed
Δ = 2.25 eV
[Rh(H2O)6]3+
Δ = 4.23 eV
4
SrMoO4 – PbMoO4
SrMoO4
PbMoO4
20
22
24
26
28
30
32
34
PbMoO4
Pb0.9Sr0.1MoO4
Pb0.8Sr0.2MoO4
Pb0.2Sr0.8MoO4
Pb0.1Sr0.9MoO4
SrMoO4
36
38
40
Pb0.5Sr0.5MoO4
Phase Diagram (Const. Temp)
Increasing Pb
SrMoO4
PbMoO4
Complete Solid Solution, Sr1-xPbxMoO4
x=0
Sr
x=0.2
Pb
x=0.5
x=0.8
x=1.0
MoO4
5
PbMoO4 - SrMoO4 Eric
100
90
80
Reflectance
70
60
PbMoO4
50
Pb(0.9)Sr(0.1)MoO4
Pb(0.8)Sr(0.2)MoO4
40
Pb(0.5)Sr(0.5)MoO4
30
Pb(0.2)Sr(0.8)MoO4
Pb(0.1)Sr(0.9)MoO4
20
SrMoO4
10
SrMoO4
0
250
350
450
550
650
PbMoO4
750
Wavelength (nm)
SrCrO4 – PbCrO4
SrCrO4
PbCrO4
20
22
24
26
28
30
32
34
PbCrO4
Pb0.9Sr0.1CrO4
Pb0.8Sr0.2CrO4
Pb0.2Sr0.8CrO4
Pb0.1Sr0.9CrO4
SrCrO4
36
38
40
Pb0.5Sr0.5CrO4
6
PbCrO4 - SrCrO4 Sachin
100
90
80
Reflectance
70
60
50
PbCrO4
40
Pb(0.9)Sr(0.1)CrO4
Pb(0.8)Sr(0.2)CrO4
30
Pb(0.5)Sr(0.5)CrO4
20
Pb(0.2)Sr(0.8)CrO4
Pb(0.1)Sr(0.9)CrO4
10
SrCrO4
SrCrO4
0
250
350
450
550
650
PbCrO4
750
Wavelength (nm)
SrMoO4 – SrCrO4
SrMoO4
SrCrO4
20
22
24
SrCrO4
Sr(CrO4)0.5(MoO4)0.5
SrMoO4
26
28
30
32
Sr(CrO4)0.9(MoO4)0.1
Sr(CrO4)0.2(MoO4)0.8
34
36
38
40
Sr(CrO4)0.8(MoO4)0.2
Sr(CrO4)0.1(MoO4)0.9
7
Phase Diagram
Increasing Mo
SrCrO4
SrCrO4
(ss)
2 Phase Region
x=0
x=0.2
SrMoO4
SrMoO4 (ss)
x=0.5
x=0.8
x=1.0
Monoclinic
Tetragonal
Sr
MoO4
CrO4
SrCrO4 - SrMoO4 Kristen
100
80
60
2-
Reflectance
70
[CrO4] absorbance
90
50
SrCrO4
SrCr0.9Mo0.1O4
SrCr0.8Mo0.2O4
SrCr0.5Mo0.5O4
40
SrCr0.2Mo0.8O4
30
SrCr0.1Mo0.9O4
SrMoO4
CrO4(2-)
20
10
SrMoO4
0
250
350
450
550
Wavelength (nm)
650
750
SrCrO4
8
PbCrO4 – PbMoO4
PbMoO4
PbCrO4
20
22
24
26
28
PbCrO4
Pb(CrO4)0.5(MoO4)0.5
30
32
Pb(CrO4)0.9(MoO4)0.1
Pb(CrO4)0.2(MoO4)0.8
34
36
38
40
Pb(CrO4)0.8(MoO4)0.2
Pb(CrO4)0.1(MoO4)0.9
PbMoO4
PbCrO4 - PbMoO4 Sam & Derek
100
90
80
Reflectance
70
60
50
PbCrO4
PbCr0.9Mo0.1O4
40
PbCr0.8Mo0.2O4
30
PbCr0.5Mo0.5O4
PbCr0.2Mo0.8O4
20
PbCr0.1Mo0.9O4
PbMoO4
10
0
250
PbMoO4
350
450
550
Wavelength (nm)
650
750
PbCrO4
9