05.06.01 10:59 PM C C r r y y s s t t a a l l F F i i e e l l d d T T h h e e o o r r y y The relationship The relationship between colors and between colors and complex metal ions complex metal ions 400 500 600 800 The relationship The relationship between colors and between colors and complex metal ions complex metal ions http://www.google.co.tz/url? http://www.google.co.tz/url? sa=t&rct=j&q=CFT+LIGHT+ABSORB sa=t&rct=j&q=CFT+LIGHT+ABSORB D+AND+OBSERVED&source=web& D+AND+OBSERVED&source=web& d=2&ved=0CCoQFjAB&url=http%3A d=2&ved=0CCoQFjAB&url=http%3A The relationship The relationship between colors and between colors and complex metal ions complex metal ions
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05.06.01 10:59 PM
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The relationship The relationship between colors and between colors and complex metal ionscomplex metal ions
400 500 600 800
The relationship The relationship between colors and between colors and complex metal ionscomplex metal ions
Crystal-Field TheoryCrystal-Field TheoryModel explaining bonding for transition metal complexesModel explaining bonding for transition metal complexes
• Originally developed to explain properties for crystalline material
• Basic idea:Electrostatic interaction between lone-pair electrons result in coordination.
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EnergeticsEnergetics
CFT - Electrostatic between metal ion CFT - Electrostatic between metal ion and donor atomand donor atom
i) Separate metal and ligand high energy
ii) Coordinated Metal - ligand stabilized
iii) Destabilization due to ligand -d electron repulsion
iv) Splitting due to octahedral field.
i
ii
iii
iv
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Ligand-Metal InteractionLigand-Metal InteractionCrystal Field Theory - Describes bonding in Metal Complexes
Basic Assumption in CFT:Electrostatic interaction between ligand and metal
d-orbitals align along the octahedral d-orbitals align along the octahedral axis will be affected the most.axis will be affected the most.
More directly the ligand attacks the More directly the ligand attacks the metal orbital, the higher the the metal orbital, the higher the the energy of the d-orbital.energy of the d-orbital.
In an octahedral field the degeneracy In an octahedral field the degeneracy of the five d-orbitals is liftedof the five d-orbitals is lifted
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d-Orbitals and Ligand Interactiond-Orbitals and Ligand Interaction(Octahedral Field)(Octahedral Field)
Ligands approach metal
d-orbitals not pointing directly at axis are least affected (stabilized) by electrostatic interaction
d-orbitals pointing directly at axis are affected most by electrostatic interaction
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Splitting of the d-OrbitalsSplitting of the d-OrbitalsOctahedral field Splitting Pattern:
The energy gap is The energy gap is referred to as referred to as ∆ ∆ (10 Dq) (10 Dq) , the , the crystal field crystal field splitting energy.splitting energy.
The dThe dz2z2 and d and dx2-y2 x2-y2 orbitals lie on the same axes as negative charges.orbitals lie on the same axes as negative charges.
Therefore, there is a large, unfavorable interaction between ligand (-) orbitals.Therefore, there is a large, unfavorable interaction between ligand (-) orbitals.
These orbitals form the degenerate high energy pair of energy levels.These orbitals form the degenerate high energy pair of energy levels.
The dThe dxyxy , d , dyxyx and d and dxzxz orbitals bisect the negative charges. orbitals bisect the negative charges.
Therefore, there is a smaller repulsion between ligand & metal for these Therefore, there is a smaller repulsion between ligand & metal for these orbitals.orbitals.
These orbitals form the degenerate low energy set of energy levels.These orbitals form the degenerate low energy set of energy levels.
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Magnitude of CF Splitting (Magnitude of CF Splitting (∆∆ or 10Dq) or 10Dq)Color of the Complex depends on magnitude of Color of the Complex depends on magnitude of ∆∆
1. Metal: Larger metal 1. Metal: Larger metal larger larger ∆∆Higher Oxidation State Higher Oxidation State larger larger ∆∆
2. Ligand: Spectrochemical series2. Ligand: Spectrochemical series
Electron Configuration in Octahedral FieldElectron Configuration in Octahedral FieldElectron configuration of metal ion:Electron configuration of metal ion:
s-electrons are lost first. s-electrons are lost first. TiTi3+3+ is a d is a d11, V, V3+3+ is d is d22 , and Cr , and Cr3+3+ is d is d33
Hund's rule:Hund's rule:First three electrons are in separate d First three electrons are in separate d orbitals with their spins parallel.orbitals with their spins parallel.
Fourth e- has choice:Fourth e- has choice:Higher orbital if Higher orbital if ∆∆ is small; High spin is small; High spinLower orbital if Lower orbital if ∆∆ is large: Low spin. is large: Low spin.
Weak field ligandsWeak field ligandsSmall Small ∆∆ , High spin complex , High spin complex
Strong field LigandsStrong field LigandsLarge Large ∆∆ , Low spin complex , Low spin complex
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High Spin Vs. Low Spin (dHigh Spin Vs. Low Spin (d11
to d to d1010
))Electron Configuration for Octahedral complexes of metal ion having dElectron Configuration for Octahedral complexes of metal ion having d11 to to dd1010 configuration [M(H configuration [M(H22O)O)66]]+n+n. .
Only the dOnly the d
44
through d through d
77
cases have both high-spin and low spin configuration cases have both high-spin and low spin configuration..
Electron configurations for octahedral complexes of metal ions
having from d
1
to d
10
configurations. Only
the d
4
through d
7
cases have both high-spin and low-spin configurations.
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Color Absorption of CoColor Absorption of Co3+3+
Complexes ComplexesThe Colors of Some Complexes of the CoThe Colors of Some Complexes of the Co3+ 3+ IonIon
The complex with fluoride ion, [CoFThe complex with fluoride ion, [CoF66]]3+3+ , is high spin and has one absorption band. , is high spin and has one absorption band. The other complexes are low spin and have two absorption bands. In all but one The other complexes are low spin and have two absorption bands. In all but one case, one of these absorptionsis in the visible region of the spectrum. The case, one of these absorptionsis in the visible region of the spectrum. The wavelengths refer to the center of that absorption band.wavelengths refer to the center of that absorption band.
Complex IonComplex Ion Wavelength of Wavelength of Color of Light Color of Light Color of ComplexColor of Complex light absorbed light absorbed Absorbed Absorbed
[CoF[CoF66
] ] 3+3+
700 (nm)700 (nm) RedRed GreenGreen
[Co(C[Co(C22
OO44
))33
] ] 3+3+
600, 420600, 420 Yellow, violetYellow, violet Dark greenDark green
310310 Ultraviolet Ultraviolet Pale YellowPale Yellow
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Colors & How We Perceive itColors & How We Perceive it
800
430
650 580
560
490
Artist color wheelArtist color wheelshowing the colors whichshowing the colors whichare complementary to oneare complementary to oneanother and the wavelengthanother and the wavelengthrange of each color.range of each color.
400
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Black Black & & WhiteWhite
If a sample absorbs all wavelength of If a sample absorbs all wavelength of visible light, none reaches our eyes visible light, none reaches our eyes from that sample. Consequently, it from that sample. Consequently, it appears black.appears black.
When a sample absorbs light, what we see is the sum When a sample absorbs light, what we see is the sum of the remaining colors that strikes our eyes.of the remaining colors that strikes our eyes.
If the sample absorbs noIf the sample absorbs novisible light, it is white visible light, it is white or colorless.or colorless.
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AbsorptionAbsorption and and ReflectionReflection
If the sample absorbsIf the sample absorbsall but all but orangeorange, the, thesample appears orange.sample appears orange.
Further, we also perceive orange color when Further, we also perceive orange color when visible light of all colors except visible light of all colors except blue blue strikes strikes our eyes. In a complementary fashion, if the our eyes. In a complementary fashion, if the sample absorbed only orange, it would appear sample absorbed only orange, it would appear blue; blue and orange are said to be blue; blue and orange are said to be complementary colors.complementary colors.
750
430
650 580
560
490
400
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Light absorption Properties of Metal ComplexesLight absorption Properties of Metal Complexes
Recording the absorption Recording the absorption SpectrumSpectrum
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Complex Influence on ColorComplex Influence on ColorCompounds of Transition metal complexes solution.Compounds of Transition metal complexes solution.
[Fe(H2
O)6
]3+
[Co(H2
O)6
]2+[Ni(H
2
O)6
]2+
[Cu(H2
O)6
]2+[Zn(H
2
O)6
]2+
800
430
650 580
560
490
400
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Color Absorption of CoColor Absorption of Co3+3+
Complexes Complexes
The Colors of Some Complexes of the Co3+ IonComplex Ion Wavelength of
Light Absorbed(nm)
Color of Light Absorbed
Color ofComplex
[CoF6]3+ 700 Red Green[Co(C2O4)3]3+ 600, 420, Yellow, violet Dark green[Co(H2O)6]3+ 600, 400, Yellow, violet Blue-green[Co(NH3)6]3+ 475, 340 Blue,
The complex with fluoride ion, [CoFThe complex with fluoride ion, [CoF66]]3+3+ , is high spin and has one absorption , is high spin and has one absorption band. The other complexes are low spin and have two absorption bands. In band. The other complexes are low spin and have two absorption bands. In all but one case, one of these absorptionsis in the visible region of the all but one case, one of these absorptionsis in the visible region of the spectrum. The wavelengths refer to the center of that absorption band.spectrum. The wavelengths refer to the center of that absorption band.
(Majority Low spin)Strong field ligandsi.e., Pd2+, Pt2+, Ir+, Au3+
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SummarySummary
Crystal Field Theory provides a basis for explaining Crystal Field Theory provides a basis for explaining many features of transition-metal complexes. many features of transition-metal complexes. Examples include why transition metal complexes are Examples include why transition metal complexes are highly colored, and why some are paramagnetic while highly colored, and why some are paramagnetic while others are diamagnetic. The spectrochemical series for others are diamagnetic. The spectrochemical series for ligands explains nicely the origin of color and ligands explains nicely the origin of color and magnetism for these compounds. There is evidence to magnetism for these compounds. There is evidence to suggest that the metal-ligand bond has covalent suggest that the metal-ligand bond has covalent character which explains why these complexes are very character which explains why these complexes are very stable. Molecular Orbital Theory can also be used to stable. Molecular Orbital Theory can also be used to describe the bonding scheme in these complexes. A describe the bonding scheme in these complexes. A more in depth analysis is required however.more in depth analysis is required however.
