Lecture 10/17/2014
Lecture 10/17/2014 Friday, October 17, 2014 12:21 PM
Ligand Field Theory for Coordination Complexes of Transition Metals
You have 3 different types of ligands 1) sigma donors 2) pi donors 3) pi acceptors --> have 3 different types of interactions btwn a ligand and metal 1) Ligand-to-metal sigma direction -electrons come from ligand to metal...going to orbital that's sigma in character -btwn sigma (filled) of the ligand and an empty valence orbital on the metal that has the correct symmetry 2) Ligand-to-metal pi donation the ligand gives the electrons, must have pi orbital that's filled (HOMO) interaction btwn filled pi orbital on the ligand and an empty valence orbital on the metal that has correct geometry/symmetry
3) Metal-to-ligand pi donation -need empty pi orbital on ligand (LUMO) -metals aren't that electronegative, so might want to give electrons back to the ligand -interaction btwn filled pi valenceorbital on metal and empty pi orbital on ligand (LUMO) that has correct symmetry -removes excess electron density from the metal --> often called pi-backdonation ligand always donates electrons through sigma bond....may or may not have pi donation like a lewis base 3 different types of interaction --> 3 types of ligands 1) sigma donors: can only do sigma donation 2) pi donors => sigma donation + pi donation 3) pi acceptors => sigma donation + pi backdonation (aka pi-backbonding) how do you know if it's pi in character? draw the MO ex: for CO....can do for any molecule for CO, HOMO = 3sigma --> sigma in character...does sigma donation LUMO = pi* --> empty and pi in character --> pi acceting (allows pi backdonation --> CO = pi acceptor
sigma-donors: .H, .CH3, alkyls, amines (NH3, NMe3) pi-donors: filled sigma bond + filled pi orbital O2-, F-, Br-, Cl-, OH-, H2O, NCO-, NCS-, R2O, ROH, RSH, R2S, SH-, RS-, Se2-, Te2-, R2N-, N3-, R2P-, RP2-, PR3 pi-acceptors: sigma filled + empty pi CO, CN-, NO, N2, RNC, b py (bispyridine)
phen:
Spectrochemical series from strongest pi accepting to least
Inorganic Chemistry Page 1
from strongest pi accepting to least
CO, CN- > phen > NO2 > NCS- > en > NH3 > H2O > F- > RCO2- > OH- > Cl- > Br- > I-
pi acceptor
sigma donor
pi donor
en = ethylenediamine
Scandium has 4s, 4p, and 3d
Inorganic Chemistry Page 2
LGO's for H's
Inorganic Chemistry Page 3
Inorganic Chemistry Page 4
Ligand Field Theory for Coordination Complexes of Transition Metals
You have 3 different types of ligands 1) sigma donors 2) pi donors 3) pi acceptors --> have 3 different types of interactions btwn a ligand and metal 1) Ligand-to-metal sigma direction -electrons come from ligand to metal...going to orbital that's sigma in character -btwn sigma (filled) of the ligand and an empty valence orbital on the metal that has the correct symmetry 2) Ligand-to-metal pi donation the ligand gives the electrons, must have pi orbital that's filled (HOMO) interaction btwn filled pi orbital on the ligand and an empty valence orbital on the metal that has correct geometry/symmetry
3) Metal-to-ligand pi donation -need empty pi orbital on ligand (LUMO) -metals aren't that electronegative, so might want to give electrons back to the ligand -interaction btwn filled pi valenceorbital on metal and empty pi orbital on ligand (LUMO) that has correct symmetry -removes excess electron density from the metal --> often called pi-backdonation ligand always donates electrons through sigma bond....may or may not have pi donation like a lewis base 3 different types of interaction --> 3 types of ligands 1) sigma donors: can only do sigma donation 2) pi donors => sigma donation + pi donation 3) pi acceptors => sigma donation + pi backdonation (aka pi-backbonding) how do you know if it's pi in character? draw the MO ex: for CO....can do for any molecule for CO, HOMO = 3sigma --> sigma in character...does sigma donation LUMO = pi* --> empty and pi in character --> pi acceting (allows pi backdonation --> CO = pi acceptor
sigma-donors: .H, .CH3, alkyls, amines (NH3, NMe3) pi-donors: filled sigma bond + filled pi orbital O2-, F-, Br-, Cl-, OH-, H2O, NCO-, NCS-, R2O, ROH, RSH, R2S, SH-, RS-, Se2-, Te2-, R2N-, N3-, R2P-, RP2-, PR3 pi-acceptors: sigma filled + empty pi CO, CN-, NO, N2, RNC, b py (bispyridine)
phen:
Spectrochemical series from strongest pi accepting to least
Inorganic Chemistry Page 1
from strongest pi accepting to least
CO, CN- > phen > NO2 > NCS- > en > NH3 > H2O > F- > RCO2- > OH- > Cl- > Br- > I-
pi acceptor
sigma donor
pi donor
en = ethylenediamine
Scandium has 4s, 4p, and 3d
Inorganic Chemistry Page 2
LGO's for H's
Inorganic Chemistry Page 3
Inorganic Chemistry Page 4
