Inorganic Unit 9

True or False: All Coordination complexes experience sigma bonding

True

Pi donor ligands typically…

have filled p orbitals

Pi acceptor ligands typically…

have unfilled p orbitals

pi donor ligands give ______ overlap

side-on

Pi donor ligands have ____ overlap

weaker

Pi acceptor ligands have _____ overlap

stronger

What type of ligand is OH- ?

sigma donor
pi donor

Phosphines are what type of ligands

sigma donors and pi acceptors
a low-lying P-R anti-bonding orbital can accept electrons in back-bonding

Define crystal field theory

An early idea based on metal in a crystal lattice. Treats metals in complexes as positive point charges in a field of negative point charges (the ligands)

Define ligand field theory

Theory that combines crystal field theory with MO theory to give a more complete understanding of coordination complex electronics rooted in bonding

What is a short-coming of crystal field theory?

Does not explain bonding or rationalize the impacts of neutral ligands

Do all ligands have a negative charge?

No

According to ligand field theory, lower _1__ orbitals are nonbonding ____(a,b,c)___

1. T2g

   a. dxy

   b. dxz
   c. dyz

For an octahedral complex, ligand pi orbitals form blank, blank, blank, and blank

3 T1g and 3 T2u non-bonding SALCs

3 T1u SALCs which interact w/ metal p orbitals

3 T2g SALCs which have a crucial interaction w/ previously nonbonding metal d orbitals.

Rank the following ligands from weakest to strongest:
OH-  I-  H2O  Cl-  F-  Br- 

I- < Br- < Cl < OH- < F- < H2O

Rank the following ligands from weakest to strongest:
NH3 NCS-(N-bound) en CN- CO PR3 bipy

NCS-(N-bound) < NH3 < en < bipy < PR3 < CN- < CO

Rank the following ligands from weakest to strongest:
Br- NH3 H2O CN- F-

Br- F- H2O NH3 CN-

Weak field ligands have ___ 𐤃

low

Strong field ligands have ___ 𐤃

high

Strong field ligands are also pi ____

acceptors

Weak field ligands are also pi ____

donors

Most labile also means…

weakest field

Least labile also means…

strongest field

True or False: More labile (weak field) ligands can be displaced by stronger field ligands

True

Higher oxidation state = ____ splitting

larger

Larger metal size = ____ splitting

larger

3d metals < 4d metals <= 5d metals

-the smaller the metal, the smaller the orbital, the smaller the overlap

The color absorbed depends on 𐤃 and can be controlled by 1 & 2

1. Metal identity/oxidation state

2. Ligand field strength
   
   stronger field ligands raise 𐤃 leading to absorption of higher energy colors like blue or violet

Draw the color wheel

Red: 650nm
Orange: 590nm
Yellow: 570nm
Green: 510nm

Blue: 475nm

Purple: 400nm

If a compound absorbs orange, you’ll see…

Blue

What are the three types of absorption?

MLCT (metal to ligand charge transfer)

LMCT (ligand to metal charge transfer)

LC (ligand centered)

To be stable, most metal complexes have ____ electrons total d and coordinating electrons

18

Square planar complexes are often stable at ___ electrons

16

This is to leave the highest d level empty

What color might you expect to see here?

Strong split suggests a big gap, so it would absorb purple and we would see yellow

What is the electron count, and do you expect this to be stable?

17e-
it is unlikely to take on another ligand since its octahedral, and it is very unlikely to be reduced to gain stability

What orbital is this

d_x²-y²

What orbital is this

d_z²

What orbital is this

d_xy

What orbital is this

d_xz

What orbital is this

d_yz

Which geometry does this represent

octahedral

Which geometry does this represent

Tetrahedral

Which geometry does this represent

Square Planar

Is this high spin or low spin

Is this high spin or low spin

What is MLCT?

Metal to Ligand Charge Transfer

What is LMCT?

Ligand to Metal Charge Transfer

What is LC?

Ligand-Centered

Identify which color is MLCT, LMCT, and LC

Blue: LC
Green: LMCT
Red: MLCT

What is the 18-electron rule?

To be stable, most metal complexes have 18 total d and coordinating electrons
• Similar to the octet rule for atoms but not derived from filling valence shell AOs