Understanding Coordination Chemistry Through

Crystal Field Theory (CFT)

Recommended Reading:Chapters 1 and 2 of Basolo and Johnson (to be posted online)

Introduction and Historical Development

Coordination Chemistry Masks “Normal” Reactivity

Color Changes With Coordination Geometry

heat

-4H2O

Octahedral, pale pinkinvisible ink when dilute: Tetrahedral, bright blue

The passwordis orbitals

heat[Co(H2O)6]Cl2 Co(H2O)2Cl2

Absorb H2O from air

Color Varies With Metal, Oxidation State, & Structure

Color Varies With Metal, Oxidation State, & Structure

Review of Geometric Isomers Terminology

Color Varies With Metal, Oxidation State, & Structure

The Difference Between the Outer and InnerCoordination Sphere

Table 1.3

Werner’s Coordination Theory1. a) Primary Valence (is related to oxidation state). Ions that balance

out the charge but are not necessarily bond tightly to the metal.b) Secondary Valence = coordination number. The groups bound to the metal are called ligands. The number of close metal ligandinteractions indicates coordination number.

2. Elements generally satisfy primary and secondary valence.

3. Secondary valence is directed towards fixed positions in space (determines sterochemistry and geometry)

A Review Exercise for You To Do at Home:

On the following Table on the next slide:

1.Circle the atoms that will bind to a metal2. Label mono-, bi-, tri-, tetra-dentate, etc. if applicable3. Guess at chelate ring size if applicable4. Which of these will form a π complex, draw this metal complex with Mn+, which could be any metal cation

Table 1.6

For you to turn in next class period (an in class exercise):1b,c,d; 2a,c; 4 which is quite hard, but attempt it

Start 1 & 2 in class now, drawing 3D picture will help w/ 1

The Coordinate Covalent Bond

Effective Atomic Number (The 18 electron rule)

The 18 electron rule

The 18 electron rule states that complexes with a total of 18 electrons surrounding the metal is especially stable.

The 18 electrons can come from a combination of the metal’s valence electrons and the ligands electrons (typically lone pairs) that are donated to the metal. Metal-metal bonds can also contribute.

The origin of this stability can be rationalized in terms of the fact that a metal that obeys the 18 electron rule is isoelectronic with a noble gas configuration.

Examples that illustrate the 18 electron rule

Examples that illustrate the 18 electron rule

Examples that illustrate the 18 electron rule

Examples that illustrate the 18 electron rule

The Octet Rule: a hard and fast rule that is rarely broken

The 18 electron rule is often broken: more of a guide to reactivity than what can/can’t occur

Motivation for Crystal Field Theory:Inconsistencies

Crystal Field Theory:An Ionic Model

Rules:1. Think about the metal and its d orbitals, the d

orbitals will all have the same energy in the absence of ligands

2. As the ligands approach the metal, think about the repulsive interaction between the ligand lone pairs and the e- in metal d orbitals:

-When a ligand is close to a d orbital, that d orbital is higher in energy due to repulsion

-The d orbitals that avoid the ligands will be lower in energy. (Electrons prefer to go into d orbitals that are lower in energy, or the ones that avoid the ligands)

An Octahedral Crystal Field

CFT Energy Diagram eg. [Ni(H2O)6]2+

E

These orbitalsavoid the ligands

Lower in E

These orbitals come near the electrons in the ligandsRepulsion Higher in E