coordination chemistry ii bonding, including crystal field theory and ligand field theory

Coordination Coordination Chemistry IIChemistry IIBonding, including crystal Bonding, including crystal

field theory and ligand field field theory and ligand field theorytheory

Basis for Bonding Basis for Bonding TheoriesTheories

Models for the bonding in Models for the bonding in transition metal complexes must be transition metal complexes must be consistent with observed behavior. consistent with observed behavior. Specific data used include stability Specific data used include stability (or formation) constants, magnetic (or formation) constants, magnetic susceptibility, and the electronic susceptibility, and the electronic (UV/Vis) spectra of the complexes.(UV/Vis) spectra of the complexes.

Bonding ApproachesBonding Approaches

Valence Bond theory provides the Valence Bond theory provides the hybridization for octahedral complexes. hybridization for octahedral complexes. For the first row transition metals, the For the first row transition metals, the hybridization can be: dhybridization can be: d22spsp3 3 (using the 3d, (using the 3d, 4s and 4p orbitals), or sp4s and 4p orbitals), or sp33dd2 2 (using the (using the 4s, 4p and 4d orbitals).4s, 4p and 4d orbitals).

The valence bond approach isn’t The valence bond approach isn’t used because it fails to explain the used because it fails to explain the electronic spectra and magnetic electronic spectra and magnetic moments of most complexes.moments of most complexes.

Crystal Field TheoryCrystal Field Theory

In crystal field theory, the In crystal field theory, the electron pairs on the ligands are electron pairs on the ligands are viewed as point negative charges viewed as point negative charges that interact with the that interact with the dd orbitals on orbitals on the central metal. The nature of the the central metal. The nature of the ligand and the tendency toward ligand and the tendency toward covalent bonding is ignored.covalent bonding is ignored.

d Orbitalsd Orbitals


Ligands, viewed as point Ligands, viewed as point charges, at the corners of an charges, at the corners of an octahedron affect the various octahedron affect the various dd orbitals differently.orbitals differently.


The The repulsion repulsion between ligand between ligand lone pairs and lone pairs and the d orbitals on the d orbitals on the metal results the metal results in a splitting of in a splitting of the energy of the energy of the d orbitals.the d orbitals.

d Orbital Splittingd Orbital Splitting

__ __ __ __ __

Spherical field

__ __dz2 dx2-y2

__ __ __dxy dxz dyz

∆o0.6∆o

0.4∆o

Octahedral field

eg

t2

g


In some texts and articles, the In some texts and articles, the gap in the d orbitals is assigned a gap in the d orbitals is assigned a value of 10Dq. The upper (evalue of 10Dq. The upper (egg) set ) set goes up by 6Dq, and the lower set goes up by 6Dq, and the lower set (t(t2g2g) goes down by 4Dq.) goes down by 4Dq.

The actual size of the gap varies The actual size of the gap varies with the metal and the ligands.with the metal and the ligands.


The colors exhibited by most The colors exhibited by most transition metal complexes arises transition metal complexes arises from the splitting of the from the splitting of the dd orbitals. orbitals. As electrons transition from the As electrons transition from the lower tlower t2g2g set to the e set to the egg set, light in the set, light in the visible range is absorbed.visible range is absorbed.

d Orbital Splittingd Orbital SplittingThe splitting The splitting

due to the nature due to the nature of the ligand can of the ligand can be observed and be observed and measured using a measured using a spectrophotometerspectrophotometer. Smaller values of . Smaller values of ∆∆oo result in colors result in colors in the green range. in the green range. Larger gaps shift Larger gaps shift the color to yellow. the color to yellow.

The Spectrochemical The Spectrochemical SeriesSeries

Based on measurements for a Based on measurements for a given metal ion, the following series given metal ion, the following series has been developed:has been developed:

II--<Br<Br--<S<S2-2-<Cl<Cl--<N<NOO33--<N<N33

--<F<F--<OH<OH--<C<C22OO442-2-

<H<H22OO

<<NNCSCS--

<CH<CH33CN<pyridine<NHCN<pyridine<NH33<en<bipy<phen<en<bipy<phen

<<NNOO22--<PPh<PPh33<<CCNN--<CO<CO

The Spectrochemical The Spectrochemical SeriesSeries

The The complexes of complexes of cobalt (III) show cobalt (III) show the shift in color the shift in color due to the ligand. due to the ligand.

(a) CN(a) CN––, (b) NO, (b) NO22––, ,

(c) phen, (d) en, (e) (c) phen, (d) en, (e) NHNH33, (f) gly, (g) , (f) gly, (g) HH22O, (h) oxO, (h) ox2–2–, (i) , (i) COCO3 3

2–2–. .

Ligand Field Strength Ligand Field Strength ObservationsObservations

1. ∆1. ∆oo increases with increasing increases with increasing oxidation number on the metal.oxidation number on the metal.

MnMn+2+2<Ni<Ni+2+2<Co<Co+2+2<Fe<Fe+2+2<V<V+2+2<Fe<Fe+3+3<Co<Co++

33

<Mn<Mn+4+4<Mo<Mo+3+3<Rh<Rh+3+3<Ru<Ru+3+3<Pd<Pd+4+4<Ir<Ir+3+3<Pt<Pt+4+4

2. ∆2. ∆oo increases with increases going increases with increases going down a group of metals.down a group of metals.

Ligand Field TheoryLigand Field Theory

Crystal Field Theory completely Crystal Field Theory completely ignores the nature of the ligand. As a ignores the nature of the ligand. As a result, it cannot explain the result, it cannot explain the spectrochemical series.spectrochemical series.

Ligand Field Theory uses a Ligand Field Theory uses a molecular orbital approach. Initially, the molecular orbital approach. Initially, the ligands can be viewed as having a hybrid ligands can be viewed as having a hybrid orbital or a orbital or a pp orbital pointing toward the orbital pointing toward the metal to make metal to make σσ bonds. bonds.

Octahedral SymmetryOctahedral Symmetry

http://www.iumsc.indiana.edu/morphology/symmetry/octahedral.html

Octahedral SymmetryOctahedral Symmetry


OOhh EE 8C8C336C6C

22

6C6C

44

3C3C2 2

(=C(=C4422))

ii6S6S

44

8S8S

66

33σσ

hh

66σσ

dd

ΓΓσσ 66 00 00 22 22 00 00 00 44 22

This reduces to A1g + Eg + T1u

Consider the group orbitals of all six ligands in octahedral geometry.


The AThe A1g 1g

group orbitals group orbitals have the same have the same symmetry as an symmetry as an ss orbital on the orbital on the central metal.central metal.


The TThe T1u 1u group group orbitals have the orbitals have the same symmetry as same symmetry as the the pp orbitals on orbitals on the central metal. the central metal.

(T (T representations representations are triply are triply degenerate.)degenerate.)


The EThe Eg g group group orbitals have the orbitals have the same symmetry as same symmetry as the dthe dzz22 and d and dxx22-y-y22 orbitals on the orbitals on the central metal. central metal.

(E representations (E representations are doubly are doubly degenerate.)degenerate.)


Since the Since the ligands don’t have a ligands don’t have a combination with combination with tt2g2g symmetry, the symmetry, the ddxyxy, d, dyzyz and d and dxyxy orbitals on the orbitals on the metal will be non-metal will be non-bonding when bonding when considering considering σσ bonding.bonding.


The molecular The molecular orbital diagram is orbital diagram is consistent with consistent with the crystal field the crystal field approach. approach.

Note that the tNote that the t2g2g set of orbitals is set of orbitals is non-bonding, and non-bonding, and the ethe egg set of set of orbitals is orbitals is antibonding.antibonding.


The The electrons from electrons from the ligands (12 the ligands (12 electrons from electrons from 6 ligands in 6 ligands in octahedral octahedral complexes) complexes) will fill the will fill the lower bonding lower bonding orbitals.orbitals.

{


The The electrons from electrons from the 4s and 3d the 4s and 3d orbitals of the orbitals of the metal (in the metal (in the first transition first transition row) will row) will occupy the occupy the middle portion middle portion of the diagram.of the diagram.

{

Experimental Evidence for Experimental Evidence for SplittingSplitting

Several tools are used to confirm the Several tools are used to confirm the splitting of the tsplitting of the t2g2g and e and egg molecular molecular orbitals. orbitals.

The broad range in colors of The broad range in colors of transition metal complexes arises from transition metal complexes arises from electronic transitions as seen in the electronic transitions as seen in the UV/visible spectra of complexes.UV/visible spectra of complexes.

Additional information is gained Additional information is gained from measuring the magnetic moments from measuring the magnetic moments of the complexes.of the complexes.

Experimental Evidence for Experimental Evidence for SplittingSplitting

Magnetic Magnetic susceptibilitysusceptibility measurements can be measurements can be used to calculate the used to calculate the number of unpaired number of unpaired electrons in a electrons in a compound.compound.

Paramagnetic Paramagnetic substances are substances are attracted to a attracted to a magnetic field.magnetic field.

Magnetic MomentsMagnetic Moments

A magnetic balance can be used to A magnetic balance can be used to determine the magnetic moment of a determine the magnetic moment of a substance. If a substance has unpaired substance. If a substance has unpaired electrons, it is electrons, it is paramagneticparamagnetic, and attracted , and attracted to a magnetic field. to a magnetic field.

For the upper transition metals, the For the upper transition metals, the spin-only magnetic moment, spin-only magnetic moment, μμss, can be used , can be used to determine the number of unpaired to determine the number of unpaired electrons.electrons.

μμss = [n(n+2)] = [n(n+2)]1/21/2


The magnetic moment of a The magnetic moment of a substance, in Bohr magnetons, can substance, in Bohr magnetons, can be related to the number of unpaired be related to the number of unpaired electrons in the compound.electrons in the compound.

μμss = [n(n+2)] = [n(n+2)]1/21/2

Where n is the number of unpaired Where n is the number of unpaired electronselectrons


Complexes with 4-7 electrons in Complexes with 4-7 electrons in the the dd orbitals have two possibilities orbitals have two possibilities for the distribution of electrons. The for the distribution of electrons. The complexes can be complexes can be low spinlow spin, in which , in which the electrons occupy the lower tthe electrons occupy the lower t2g2g set and pair up, or they can be set and pair up, or they can be high high spinspin. In these complexes, the . In these complexes, the electrons will fill the upper eelectrons will fill the upper egg set set before pairing.before pairing.

High and Low Spin High and Low Spin ComplexesComplexes

If the gap If the gap between the between the dd orbitals is large, orbitals is large, electrons will pair up electrons will pair up and fill the lower (tand fill the lower (t2g2g) ) set of orbitals before set of orbitals before occupying the eoccupying the egg set set of orbitals.of orbitals. The The complexes are called complexes are called low spinlow spin..


In low spin In low spin complexes, the complexes, the size of ∆size of ∆oo is is greater than the greater than the pairing energy pairing energy of the electrons.of the electrons.


If the gap If the gap between the between the dd orbitals is small, orbitals is small, electrons will occupy electrons will occupy the ethe egg set of orbitals set of orbitals before they pair up before they pair up and fill the lower (tand fill the lower (t2g2g) ) set of orbitals before.set of orbitals before.

The complexes The complexes are called are called high spinhigh spin..


In high In high spin complexes, spin complexes, the size of ∆the size of ∆oo is is less than the less than the pairing energy pairing energy of the of the electrons.electrons.

Ligand Field Ligand Field Stabilization EnergyStabilization Energy

The first row transition metals The first row transition metals in water are all weak field, high spin in water are all weak field, high spin cases.cases.

ddoo dd11 dd22 dd33 dd44 dd55

dd66

dd77 dd88 dd99 dd1010

LFSLFSEE

00 .4.4ΔΔ

oo

.8.8 1.21.2 .6.6 00 .4.4 .8.8 1.21.2 .6.6 00

Experimental Evidence Experimental Evidence for LFSEfor LFSE

The hydration energies of the The hydration energies of the first row first row

transition metals should increase transition metals should increase across the period as the size of the across the period as the size of the metal ion gets smaller.metal ion gets smaller.

MM2+ 2+ + 6 H+ 6 H22O(l) O(l) M(H M(H22O)O)662+2+

Experimental Evidence Experimental Evidence for LFSEfor LFSE

The heats of The heats of hydration show two hydration show two “humps” consistent “humps” consistent with the expected with the expected LFSE for the metal LFSE for the metal ions. The values for ions. The values for dd55 and d and d1010 are the are the same as expected same as expected with a LFSE equal with a LFSE equal to 0.to 0.

Experimental Evidence of Experimental Evidence of LFSELFSE

ddoo dd11 dd22

dd33 dd44

dd55

dd66

dd77 dd88 dd99 dd1010

LFSLFSEE

00 .4.4ΔΔ

oo

.8.8 1.1.22

..66

00 .4.4 .8.8 1.1.22

.6.6 00

High Spin vs. Low SpinHigh Spin vs. Low Spin

3d metals3d metals are are generally high spingenerally high spin complexes except with very strong complexes except with very strong ligands. CNligands. CN-- forms low spin forms low spin complexes, especially with Mcomplexes, especially with M3+3+ ions. ions.

4d & 4d metals4d & 4d metals generally have a larger generally have a larger value of ∆value of ∆oo than for 3d metals. As a than for 3d metals. As a result, complexes are result, complexes are typically low typically low spinspin. .

Effect of Metal Charge on Splitting

Nature of the LigandsNature of the Ligands

Crystal field theory and ligand field Crystal field theory and ligand field theory differ in that LFT considers the theory differ in that LFT considers the nature of the ligands. Thus far, we nature of the ligands. Thus far, we have only viewed the ligands as have only viewed the ligands as electron pairs used for making electron pairs used for making σσ bonds bonds with the metal. Many ligands can also with the metal. Many ligands can also form form ππ bonds with the metal. Group bonds with the metal. Group theory greatly simplifies the theory greatly simplifies the construction of molecular orbital construction of molecular orbital diagrams.diagrams.

Considering Considering ππ Bonding Bonding

To obtain To obtain ΓΓredred for for ππ bonding, a bonding, a set of cartesian coordinates is set of cartesian coordinates is established for each of the ligands. established for each of the ligands. The direction of the The direction of the σσ bonds is bonds is arbitrarily set as the arbitrarily set as the yy axis (or the p axis (or the pyy orbitals). The porbitals). The pxx and p and pzz orbitals are orbitals are used in used in ππ bonding. bonding.

Considering Considering ππ BondingBonding

y y

y

y y

y

x

x

x

x

x

x

zz

z

z

zz

OOhh EE 8C8C336C6C

22

6C6C

44

3C3C2 2

(=C(=C4422))

ii6S6S

44

8S8S

66

33σσ

hh

66σσ

dd

ΓΓππ1122

00 00 00 -4-4 00 00 00 00 00

Consider only the px and pz orbitals on each of the ligands to obtain Γπ.

Considering Considering ππ Bonding Bonding

This reduces to TThis reduces to T1g1g + T + T2g2g + T + T1u1u + T + T2u2u. The T. The T2g2g set has the same symmetry as the dset has the same symmetry as the dxyxy, d, dyzyz and d and dxzxz orbitals on the metal. The Torbitals on the metal. The T1u1u set has the same set has the same symmetry as the psymmetry as the pxx, p, pyy and p and pzz orbitals on the orbitals on the metal.metal.

OOhh EE 8C8C336C6C

22

6C6C

44

3C3C2 2

(=C(=C4422))

ii6S6S

44

8S8S

66

33σσ

hh

66σσ

dd

ΓΓππ1122

00 00 00 -4-4 00 00 00 00 00

Considering Considering ππ Bonding Bondingππ reduces to: T reduces to: T1g1g + T + T2g2g + T + T1u1u + T + T2u2u. .

The TThe T1g1g and T and T2u2u group orbitals for the ligands don’t group orbitals for the ligands don’t match the symmetry of any of the metal orbitals.match the symmetry of any of the metal orbitals.

The TThe T1u1u set has the same symmetry as the p set has the same symmetry as the pxx, p, pyy and pand pzz orbitals on the metal. These orbitals are orbitals on the metal. These orbitals are used primarily to make the used primarily to make the σσ bonds to the ligands. bonds to the ligands.

The TThe T2g2g set has the same symmetry as the d set has the same symmetry as the dxyxy, d, dyzyz and dand dxzxz orbitals on the metal. orbitals on the metal.

ππ Bonding Bonding

The main source of The main source of ππ bonding is bonding is between the dbetween the dxyxy, d, dyzyz and d and dxzxz orbitals orbitals on the metal and the d, p or on the metal and the d, p or ππ* * orbitals on the ligand.orbitals on the ligand.


The ligand may have empty d or The ligand may have empty d or ππ* orbitals and serve as a * orbitals and serve as a ππ acceptor acceptor ligand, or full p or d orbitals and ligand, or full p or d orbitals and serve as a serve as a ππ donor donor ligand.ligand.


The empty The empty ππ antibonding orbital antibonding orbital on CO can accept electron density on CO can accept electron density from a filled from a filled dd orbital on the metal. orbital on the metal. CO is a CO is a pi acceptorpi acceptor ligand. ligand.

empty π* orbital

filled d orbital

ππ Donor Ligands (L Donor Ligands (LM)M)

All ligands are All ligands are σσ donors. donors. Ligands with filled Ligands with filled pp or or d d orbitals orbitals may also serve as pi donor ligands. may also serve as pi donor ligands. Examples of Examples of ππ donor ligands are I donor ligands are I--, , ClCl--, and S, and S2-2-. The filled p or d orbitals . The filled p or d orbitals on these ions interact with the ton these ions interact with the t2g2g set set of orbitals (dof orbitals (dxyxy, d, dyzyz and d and dxzxz) on the ) on the metal to form bonding and metal to form bonding and antibonding molecular orbitals.antibonding molecular orbitals.

ππ Donor Ligands (L Donor Ligands (LM)M)

The bonding The bonding orbitals, which are orbitals, which are lower in energy, are lower in energy, are primarily filled with primarily filled with electrons from the electrons from the ligand, the and ligand, the and antibonding molecular antibonding molecular orbitals are primarily orbitals are primarily occupied by electrons occupied by electrons from the metal.from the metal.

σσ Bonding vs. Bonding vs. Bonding Bonding

ππ Donor Ligands (L Donor Ligands (LM)M)The size of ∆The size of ∆oo

decreases, since it is decreases, since it is now between an now between an antibonding tantibonding t2g2g orbital orbital and the eand the egg* orbital.* orbital.

This is confirmed This is confirmed by the spectrochemical by the spectrochemical series. Weak field series. Weak field ligands are also pi ligands are also pi donor ligands.donor ligands.

ππ Acceptor Ligands Acceptor Ligands (M(ML)L)

Ligands such Ligands such as CN, Nas CN, N22 and CO and CO have empty have empty ππ antibonding antibonding orbitals of the orbitals of the proper symmetry proper symmetry and energy to and energy to interact with filled interact with filled dd orbitals on the orbitals on the metal.metal.


The metal uses The metal uses the tthe t2g2g set of orbitals set of orbitals (d(dxyxy, d, dyzyz and d and dxzxz) to ) to engage in pi bonding engage in pi bonding with the ligand. The with the ligand. The ππ* orbitals on the * orbitals on the ligand are usually ligand are usually higher in energy than higher in energy than the d orbitals on the the d orbitals on the metal.metal.


The The interaction causes interaction causes the energy of the the energy of the tt2g2g bonding bonding orbitals to drop orbitals to drop slightly, thus slightly, thus increasing the increasing the size of ∆size of ∆oo..

Effect of Ligand on Splitting

SummarySummary

1. All ligands are 1. All ligands are σσ donors. In general, donors. In general, ligands that engage solely in ligands that engage solely in σσ bonding are in the middle of the bonding are in the middle of the spectrochemical series. Some very spectrochemical series. Some very strong strong σσ donors, such as CH donors, such as CH33

-- and H and H-- are found high in the series.are found high in the series.

2. Ligands with filled 2. Ligands with filled pp or or dd orbitals orbitals can also serve as can also serve as ππ donors. This donors. This results in a smaller value of ∆results in a smaller value of ∆oo..

SummarySummary

3. Ligands with empty 3. Ligands with empty pp, , dd or or ππ* * orbitals can also serve as orbitals can also serve as ππ acceptors. This results in a larger acceptors. This results in a larger value of ∆value of ∆oo..

II--<Br<Br--<Cl<Cl--<F<F--<H<H22O<NHO<NH33<PPh<PPh33<CO<CO

ππ donor< weak donor< weak ππ donor< donor<σσ only< only< ππ acceptor acceptor

4 – Coordinate 4 – Coordinate ComplexesComplexes

Square planar and tetrahedral Square planar and tetrahedral complexes are quite common for complexes are quite common for certain transition metals. The certain transition metals. The splitting patterns of the splitting patterns of the dd orbitals on orbitals on the metal will differ depending on the metal will differ depending on the geometry of the complex.the geometry of the complex.

Tetrahedral ComplexesTetrahedral Complexes

The dThe dzz2 2 and dand dxx22-y-y2 2

orbitals point directly orbitals point directly between the ligands in between the ligands in a tetrahedral a tetrahedral arrangement. As a arrangement. As a result, these two result, these two orbitals, designated as orbitals, designated as ee in the point group in the point group TTdd, , are lower in energy.are lower in energy.

Tetrahedral ComplexesTetrahedral ComplexesThe The tt22 set of orbitals, set of orbitals,

consisting of the dconsisting of the dxyxy, d, dyzyz, , and dand dxzxz orbitals, are orbitals, are directed more in the directed more in the direction of the ligands. direction of the ligands.

These orbitals will These orbitals will be higher in energy in a be higher in energy in a tetrahedral field due to tetrahedral field due to repulsion with the repulsion with the electrons on the ligands. electrons on the ligands.

Tetrahedral ComplexesTetrahedral ComplexesThe size of the The size of the

splitting, splitting, ∆∆TT, is , is considerably smaller considerably smaller than with comparable than with comparable octahedral complexes. octahedral complexes. This is because only 4 This is because only 4 bonds are formed, and bonds are formed, and the metal orbitals used in the metal orbitals used in bonding don’t point right bonding don’t point right at the ligands as they do at the ligands as they do in octahedral complexes.in octahedral complexes.

Tetrahedral ComplexesTetrahedral Complexes

In general, ∆In general, ∆TT ≈ 4/9 ∆≈ 4/9 ∆oo. Since . Since the splitting is the splitting is smaller, all smaller, all tetrahedral tetrahedral complexes are complexes are weak-field, high-weak-field, high-spin cases.spin cases.

Tetragonal Complexes Tetragonal Complexes

Six coordinate complexes, Six coordinate complexes, notably those of Cunotably those of Cu2+2+, distort from , distort from octahedral geometry. One such octahedral geometry. One such distortion is called distortion is called tetragonal tetragonal distortiondistortion, in which the bonds along , in which the bonds along one axis elongate, with compression one axis elongate, with compression of the bond distances along the of the bond distances along the other two axes.other two axes.

Tetragonal Complexes Tetragonal Complexes The elongation The elongation

along the along the zz axis axis causes the causes the dd orbitals with density orbitals with density along the axis to along the axis to drop in energy. As drop in energy. As a result, the da result, the dxzxz and and ddyzyz orbitals lower in orbitals lower in energy.energy.


The The compression along compression along the the xx and and yy axis axis causes orbitals causes orbitals with density along with density along these axes to these axes to increase in increase in energy. energy.

..


For complexes For complexes with 1-3 electrons with 1-3 electrons in the ein the egg set of set of orbitals, this type orbitals, this type of tetragonal of tetragonal distortion may distortion may lower the energy lower the energy of the complex.of the complex.

Square Planar Square Planar ComplexesComplexes For complexes with For complexes with

2 electrons in the e2 electrons in the egg set set of orbitals, a dof orbitals, a d88 configuration, a severe configuration, a severe distortion may occur, distortion may occur, resulting in a 4-resulting in a 4-coordinate square planar coordinate square planar shape, with the ligands shape, with the ligands along the along the zz axis no axis no longer bonded to the longer bonded to the metal.metal.

Square Planar Square Planar ComplexesComplexes Square planar Square planar complexes are quite complexes are quite common for the dcommon for the d88 metals in the 4metals in the 4thth and 5 and 5thth periods: Rh(I), IR(I), periods: Rh(I), IR(I), Pt(II), Pd(II) and Au(III). Pt(II), Pd(II) and Au(III). The lower transition The lower transition metals have large metals have large ligand field stabilization ligand field stabilization energies, favoring four-energies, favoring four-coordinate complexes.coordinate complexes.

Square Planar Square Planar ComplexesComplexes Square planar Square planar

complexes are rare for complexes are rare for the 3the 3rdrd period metals. period metals. Ni(II) generally forms Ni(II) generally forms tetrahedral complexes. tetrahedral complexes. Only with very strong Only with very strong ligands such as CNligands such as CN--, is , is square planar square planar geometry seen with geometry seen with Ni(II). Ni(II).

Square Planar Square Planar ComplexesComplexes

The value of ∆The value of ∆spsp for a given metal, for a given metal, ligands and bond ligands and bond length is length is approximately approximately 1.3(∆1.3(∆oo). ).

The Jahn-Teller EffectThe Jahn-Teller Effect

If the ground electronic If the ground electronic configuration of a non-linear configuration of a non-linear complex is orbitally degenerate, the complex is orbitally degenerate, the complex will distort so as to remove complex will distort so as to remove the degeneracy and achieve a lower the degeneracy and achieve a lower energy.energy.


The Jahn-Teller effect predicts The Jahn-Teller effect predicts which structures will distort. It does which structures will distort. It does not predict the nature or extent of not predict the nature or extent of the distortion. The effect is most the distortion. The effect is most often seen when the orbital often seen when the orbital degneracy is in the orbitals that degneracy is in the orbitals that point directly towards the ligands.point directly towards the ligands.


In octahedral complexes, the In octahedral complexes, the effect is most pronounced in high effect is most pronounced in high spin dspin d44, low spin d, low spin d7 7 and dand d99 configurations, as the degeneracy configurations, as the degeneracy occurs in the eoccurs in the egg set of orbitals. set of orbitals.

d4 d7 d9

eg

t2g


The strength of the Jahn-Teller The strength of the Jahn-Teller effect is tabulated below: (w=weak, effect is tabulated below: (w=weak, s=strong)s=strong)

# e# e-- 11 22 33 44 55 66 77 88 991100

High High spinspin ** ** ** ss -- ww ww ** ** **

Low Low spinspin ww ww -- ww ww -- ss -- ss --

*There is only 1 possible ground state configuration.- No Jahn-Teller distortion is expected.

coordination chemistry ii bonding, including crystal field theory and ligand field theory

Documents

ligand field theorybasis

various d orbitals

spherical field

transition metal complexes

d orbital splittingthe

central metal

s orbital

metal results