Slide 1

Teori Medan Ligan(Teori Orbital Molekul)

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Metal-ligand s interactions in an octahedral environmentSix ligand orbitals of s symmetry approaching the metal ion along the x,y,z axesWe can build 6 group orbitals of s symmetry as beforeand work out the reducible representation

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sIf you are given G, you know by now how to get the irreducible representations

G = A1g + T1u + Eg3

sNow we just match the orbital symmetries

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Orbital Molekul Kompleks Oktahedral (ikatan saja)5

Introducing -bonding2 orbitals of -symmetryon each ligandWe can build 12 group orbitalsof -symmetry

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G = T1g + T2g + T1u + T2u

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Anti-bonding LUMO()The CN- ligand

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Some schematic diagrams showing how bonding occurs with a ligand having a d orbital (P), a p* orbital, and a vacant p orbital.9

6 s ligands x 2e each12 s bonding eligand characterd0-d10 electronsnon bondinganti bondingmetal characterML6 s-only bondingThe bonding orbitals, essentially the ligand lone pairs, will not be worked with further.10t2geg

t2gML6s-onlyML6s + Stabilization(empty -orbitals on ligands)DoDoDo has increased-bonding may be introducedas a perturbation of the t2g/eg set:Case 1 (CN-, CO, C2H4)empty -orbitals on the ligandsML -bonding (-back bonding)t2g ()t2g (*)eg11t2gegt2gML6s-onlyML6s + -bonding may be introducedas a perturbation of the t2g/eg set.Case 2 (Cl-, F-) filled -orbitals on the ligandsLM -bonding(filled -orbitals)

StabilizationDestabilizationt2g ()t2g (*)egDoDoDo has decreased12

Strong field / low spinWeak field / high spinPutting it all on one diagram.13Spectrochemical SeriesPurely s ligands: D: en > NH3 (order of proton basicity) donating which decreases splitting and causes high spin:D: H2O > F > RCO2 > OH > Cl > Br > I (also proton basicity)Adding in water, hydroxide and carboxylateD: H2O > F > RCO2 > OH > Cl > Br > Ip accepting ligands increase splitting and may be low spinD: CO, CN-, > phenanthroline > NO2- > NCS-

14Merging to get spectrochemical seriesCO, CN- > phen > en > NH3 > NCS- > H2O > F- > RCO2- > OH- > Cl- > Br- > I-Strong field, p acceptors large D low spins onlyWeak field, p donors small D high spin

15Turning to Square Planar Complexes

Most convenient to use a local coordinate system on each ligand with y pointing in towards the metal. py to be used for s bonding.z being perpendicular to the molecular plane. pz to be used for p bonding perpendicular to the plane, p^. x lying in the molecular plane. px to be used for p bonding in the molecular plane, p|.

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ML4 square planar complexesligand group orbitals and matching metal orbitals

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ML4 square planar complexesMO diagrams-only bonding

- bonding18

A crystal-field aproach: from octahedral to square planar

Less repulsions along the axeswhere ligands are missing

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A crystal-field aproach: from octahedral to tetrahedral

A correction to preservecenter of gravity

20The Jahn-Teller effectJahn-Teller theorem: there cannot be unequal occupation of orbitals with identical energyMolecules will distort to eliminate the degeneracy

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