CHEM 522 Chapter 01 Introduction

Transition Metal Organometallic Chemistry Organic versus inorganic chemistry Transition metals –Oxidation state –d orbitals Ligands (L) Coordination compounds or complexes (ML n )

Werner Complexes Lewis acids and bases Common types –Octahedral ML 6 –Tetrahedral ML 4 –Square planar ML 4 –Trigonal bipyramid ML 5 –Square pyramid ML 5 Stereochemistry –cis, trans isomers –optical isomers

Bridging When the ligand have more than one site for binding it could make a bridge 3c-2e bond

Chelate Effect Chelating ligand can bind through more than one donor atom Example ethylene diamine Chelating ligands are favored from entropy point of view M(NH 3 ) 6 n+ + 3en  M(en) 3 n+ + 6NH 3

The Trans Effect Trans influence: certain ligands make ligands trans to it more labile. For platinum complexes the order is: OH - < NH 3 < Cl - < CN -, CO < PR 3 < H -

Hard and Soft Bases Hard base small and high charge Soft base large and low charge Soft-soft and hard-hard interaction is prefer over hard-soft interaction

Effect of ligands on d-orbitals

Octahedral Complex and d-Orbital Energies

Crystal Field Theory

Energy Effects in Octahedral Complexes

Crystal Field Theory

∆ o versus P Hund’s rule pairing energy considerations ∆ > Plow spin ∆ < Phigh spin

Magnetic Properties of Coordination Compounds and Crystal Field Theory.

Magnetic moment Magnetic moment μ s μ s = √n(n+2) Where n = number of unpaired electrons n μ s

Colors of Transition-Metal Complexes Transition-metal complexes can be red, purple, blue, green, yellow, orange, etc. Most other compounds are colorless (or, white). Why are transition-metal complexes special?

Absorption of Light If a compound is colored, it must absorb visible light. To absorb visible light a compound must have an empty (or partially filled) electronic energy level that is just a little higher in energy than another filled (or partially filled) level. The d orbitals in transition-metal ions often meet this test.

t 2g 1 e g 0 –> t 2g 0 e g 1

Spectrochemical Series Ligands can be arranged into a spectrochemical series according to the magnitude of splitting of the d-orbitals Large splitting is associated with strong field ligands Small splitting is associated with weak field ligands CN -1 >en>NH 3 >H 2 O>F - >SCN - > Cl - > Br - > I -

Crystal field splitting

Weak and Strong Field Ligands

Tetrahedral Crystal Field

Tetrahedral Splitting Pattern of d-Orbitals ∆ O >∆ T thus no strong field vs. weak field cases

Square Planar Crystal Field

Pi Bond Donor

Pi Bond Acceptor

Interaction with л-donor ligands

Interaction with л-acceptor ligands

л-donor ligands л-acceptor ligands

MO diagram of M(CO) 6

Types of Ligands Simple sigma (σ)donor M-ClM-NH 3 M can also bond to C=C л bond and H-H σ bond This is known as hapticity (η) η 2 H 2 CCH 2 η 2 H 2

M-H 2 Bond (η 2 )

Interaction with Double Bond (η 2 )

Interaction with Double Bond

(η 5 ) (η 1 )

Type of Ligands σ bonding electron pair donors (always consider 2-e are donated by ligand so ligand will be NH 3, H -, R 3 C -, σ bonding, strong л-acceptor CO, CN -, PR 3, σ bonding л-donor Cl -, F -, л-bonding electron pair donor л-acceptor C 2 H 4, O 2,

Common Ligands Table 1.10 CO, CN - C p PR 3 bipy dpe acac